diff --git a/compiler/rustc/Cargo.toml b/compiler/rustc/Cargo.toml
index 37f90bf3c1008..277cf0f51d378 100644
--- a/compiler/rustc/Cargo.toml
+++ b/compiler/rustc/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc-main"
 version = "0.0.0"
-edition = '2018'
+edition = "2021"
 
 [dependencies]
 rustc_driver = { path = "../rustc_driver" }
diff --git a/compiler/rustc_apfloat/Cargo.toml b/compiler/rustc_apfloat/Cargo.toml
index 9f266b1fb978d..bb01d4f51b899 100644
--- a/compiler/rustc_apfloat/Cargo.toml
+++ b/compiler/rustc_apfloat/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_apfloat"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 bitflags = "1.2.1"
diff --git a/compiler/rustc_arena/Cargo.toml b/compiler/rustc_arena/Cargo.toml
index eba8a2a082f3e..33ccd0445030f 100644
--- a/compiler/rustc_arena/Cargo.toml
+++ b/compiler/rustc_arena/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_arena"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 rustc_data_structures = { path = "../rustc_data_structures" }
diff --git a/compiler/rustc_ast/Cargo.toml b/compiler/rustc_ast/Cargo.toml
index 67cf5d92b00cb..58b967a370415 100644
--- a/compiler/rustc_ast/Cargo.toml
+++ b/compiler/rustc_ast/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_ast"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_ast_lowering/Cargo.toml b/compiler/rustc_ast_lowering/Cargo.toml
index 4e848a6a2b8fb..f4859ee4ae91f 100644
--- a/compiler/rustc_ast_lowering/Cargo.toml
+++ b/compiler/rustc_ast_lowering/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_ast_lowering"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_ast_passes/Cargo.toml b/compiler/rustc_ast_passes/Cargo.toml
index 4a6eb80fb30ce..9312a68bc600c 100644
--- a/compiler/rustc_ast_passes/Cargo.toml
+++ b/compiler/rustc_ast_passes/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_ast_passes"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 itertools = "0.9"
diff --git a/compiler/rustc_ast_pretty/Cargo.toml b/compiler/rustc_ast_pretty/Cargo.toml
index fa88740103ba3..29f2be4cf4648 100644
--- a/compiler/rustc_ast_pretty/Cargo.toml
+++ b/compiler/rustc_ast_pretty/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_ast_pretty"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_attr/Cargo.toml b/compiler/rustc_attr/Cargo.toml
index 0566379e1f5e1..ba310a6860e82 100644
--- a/compiler/rustc_attr/Cargo.toml
+++ b/compiler/rustc_attr/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_attr"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_borrowck/Cargo.toml b/compiler/rustc_borrowck/Cargo.toml
index c683c388ba9ea..75e9c69af4e5c 100644
--- a/compiler/rustc_borrowck/Cargo.toml
+++ b/compiler/rustc_borrowck/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_borrowck"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_builtin_macros/Cargo.toml b/compiler/rustc_builtin_macros/Cargo.toml
index 2370ac201b018..fd34f947f72c0 100644
--- a/compiler/rustc_builtin_macros/Cargo.toml
+++ b/compiler/rustc_builtin_macros/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_builtin_macros"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_codegen_cranelift/Cargo.toml b/compiler/rustc_codegen_cranelift/Cargo.toml
index 6f40fc0fcb881..61d40702a3284 100644
--- a/compiler/rustc_codegen_cranelift/Cargo.toml
+++ b/compiler/rustc_codegen_cranelift/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_codegen_cranelift"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 crate-type = ["dylib"]
diff --git a/compiler/rustc_codegen_cranelift/src/bin/cg_clif_build_sysroot.rs b/compiler/rustc_codegen_cranelift/src/bin/cg_clif_build_sysroot.rs
index e7cd5edbbf654..89e0cb8d90ecd 100644
--- a/compiler/rustc_codegen_cranelift/src/bin/cg_clif_build_sysroot.rs
+++ b/compiler/rustc_codegen_cranelift/src/bin/cg_clif_build_sysroot.rs
@@ -8,7 +8,6 @@
 
 #![feature(rustc_private)]
 
-extern crate rustc_data_structures;
 extern crate rustc_driver;
 extern crate rustc_interface;
 extern crate rustc_session;
diff --git a/compiler/rustc_codegen_llvm/Cargo.toml b/compiler/rustc_codegen_llvm/Cargo.toml
index 3c99febbd57cc..3f02443458188 100644
--- a/compiler/rustc_codegen_llvm/Cargo.toml
+++ b/compiler/rustc_codegen_llvm/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_codegen_llvm"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 test = false
diff --git a/compiler/rustc_codegen_ssa/Cargo.toml b/compiler/rustc_codegen_ssa/Cargo.toml
index 1446624b88157..0713e167c53b8 100644
--- a/compiler/rustc_codegen_ssa/Cargo.toml
+++ b/compiler/rustc_codegen_ssa/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_codegen_ssa"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 test = false
diff --git a/compiler/rustc_const_eval/Cargo.toml b/compiler/rustc_const_eval/Cargo.toml
index 1653d5cf6c560..a51273732ae6f 100644
--- a/compiler/rustc_const_eval/Cargo.toml
+++ b/compiler/rustc_const_eval/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_const_eval"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index a6375ad0e02cf..fc69770bf6a30 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -77,7 +77,7 @@ macro_rules! throw_validation_failure {
 ///
 macro_rules! try_validation {
     ($e:expr, $where:expr,
-    $( $( $p:pat )|+ => { $( $what_fmt:expr ),+ } $( expected { $( $expected_fmt:expr ),+ } )? ),+ $(,)?
+    $( $( $p:pat_param )|+ => { $( $what_fmt:expr ),+ } $( expected { $( $expected_fmt:expr ),+ } )? ),+ $(,)?
     ) => {{
         match $e {
             Ok(x) => x,
diff --git a/compiler/rustc_data_structures/Cargo.toml b/compiler/rustc_data_structures/Cargo.toml
index bc13ca26e2e22..4996257012970 100644
--- a/compiler/rustc_data_structures/Cargo.toml
+++ b/compiler/rustc_data_structures/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_data_structures"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_driver/Cargo.toml b/compiler/rustc_driver/Cargo.toml
index ba8616cc6ef73..6721e00027d42 100644
--- a/compiler/rustc_driver/Cargo.toml
+++ b/compiler/rustc_driver/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_driver"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 crate-type = ["dylib"]
diff --git a/compiler/rustc_error_codes/Cargo.toml b/compiler/rustc_error_codes/Cargo.toml
index 270e5301895a4..7d5f3e4672a0f 100644
--- a/compiler/rustc_error_codes/Cargo.toml
+++ b/compiler/rustc_error_codes/Cargo.toml
@@ -1,4 +1,4 @@
 [package]
 name = "rustc_error_codes"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
diff --git a/compiler/rustc_errors/Cargo.toml b/compiler/rustc_errors/Cargo.toml
index c74fd60e530c1..4846dc43605f8 100644
--- a/compiler/rustc_errors/Cargo.toml
+++ b/compiler/rustc_errors/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_errors"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index b1526cf78d2e9..03e8534ef289f 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -1028,15 +1028,13 @@ impl HandlerInner {
             let mut error_codes = self
                 .emitted_diagnostic_codes
                 .iter()
-                .filter_map(|x| {
-                    match &x {
+                .filter_map(|x| match &x {
                     DiagnosticId::Error(s)
-                        if let Ok(Some(_explanation)) = registry.try_find_description(s) =>
+                        if registry.try_find_description(s).map_or(false, |o| o.is_some()) =>
                     {
                         Some(s.clone())
                     }
                     _ => None,
-                }
                 })
                 .collect::<Vec<_>>();
             if !error_codes.is_empty() {
diff --git a/compiler/rustc_expand/Cargo.toml b/compiler/rustc_expand/Cargo.toml
index 1be9321e4fed5..45237ab2e9f25 100644
--- a/compiler/rustc_expand/Cargo.toml
+++ b/compiler/rustc_expand/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_expand"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 build = false
 
 [lib]
diff --git a/compiler/rustc_feature/Cargo.toml b/compiler/rustc_feature/Cargo.toml
index ee381e34251b5..3d8d0db20d122 100644
--- a/compiler/rustc_feature/Cargo.toml
+++ b/compiler/rustc_feature/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_feature"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_fs_util/Cargo.toml b/compiler/rustc_fs_util/Cargo.toml
index c417e978b311d..34c3fe2a005c8 100644
--- a/compiler/rustc_fs_util/Cargo.toml
+++ b/compiler/rustc_fs_util/Cargo.toml
@@ -1,4 +1,4 @@
 [package]
 name = "rustc_fs_util"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
diff --git a/compiler/rustc_graphviz/Cargo.toml b/compiler/rustc_graphviz/Cargo.toml
index 87c41ae171ef5..d657fdb1a7789 100644
--- a/compiler/rustc_graphviz/Cargo.toml
+++ b/compiler/rustc_graphviz/Cargo.toml
@@ -1,4 +1,4 @@
 [package]
 name = "rustc_graphviz"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
diff --git a/compiler/rustc_hir/Cargo.toml b/compiler/rustc_hir/Cargo.toml
index 61b941fd756fc..3b6e6db72d1f7 100644
--- a/compiler/rustc_hir/Cargo.toml
+++ b/compiler/rustc_hir/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_hir"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_hir_pretty/Cargo.toml b/compiler/rustc_hir_pretty/Cargo.toml
index c7510b7ec1422..46a8e7deeed04 100644
--- a/compiler/rustc_hir_pretty/Cargo.toml
+++ b/compiler/rustc_hir_pretty/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_hir_pretty"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_incremental/Cargo.toml b/compiler/rustc_incremental/Cargo.toml
index 9156243a10c0a..dece752c1945f 100644
--- a/compiler/rustc_incremental/Cargo.toml
+++ b/compiler/rustc_incremental/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_incremental"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_index/Cargo.toml b/compiler/rustc_index/Cargo.toml
index e1a2b619763f2..b984a1321e0aa 100644
--- a/compiler/rustc_index/Cargo.toml
+++ b/compiler/rustc_index/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_index"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_infer/Cargo.toml b/compiler/rustc_infer/Cargo.toml
index 15649bb678e24..f87ea43b1a72c 100644
--- a/compiler/rustc_infer/Cargo.toml
+++ b/compiler/rustc_infer/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_infer"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_interface/Cargo.toml b/compiler/rustc_interface/Cargo.toml
index e76fa6d8a1bc6..07af2201f5fc2 100644
--- a/compiler/rustc_interface/Cargo.toml
+++ b/compiler/rustc_interface/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_interface"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index a5f0c01477898..3d90a6c934536 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -125,6 +125,7 @@ pub fn scoped_thread<F: FnOnce() -> R + Send, R: Send>(cfg: thread::Builder, f:
     let result_ptr = Ptr(&mut result as *mut _ as *mut ());
 
     let thread = cfg.spawn(move || {
+        let _ = (&run, &result_ptr);
         let run = unsafe { (*(run.0 as *mut Option<F>)).take().unwrap() };
         let result = unsafe { &mut *(result_ptr.0 as *mut Option<R>) };
         *result = Some(run());
diff --git a/compiler/rustc_lexer/Cargo.toml b/compiler/rustc_lexer/Cargo.toml
index 7e05fe545cabe..60c146f457b42 100644
--- a/compiler/rustc_lexer/Cargo.toml
+++ b/compiler/rustc_lexer/Cargo.toml
@@ -2,7 +2,7 @@
 name = "rustc_lexer"
 version = "0.1.0"
 license = "MIT OR Apache-2.0"
-edition = "2018"
+edition = "2021"
 
 repository = "https://github.com/rust-lang/rust/"
 description = """
diff --git a/compiler/rustc_lint/Cargo.toml b/compiler/rustc_lint/Cargo.toml
index 8294d5878fa99..414fcbeb9e415 100644
--- a/compiler/rustc_lint/Cargo.toml
+++ b/compiler/rustc_lint/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_lint"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 if_chain = "1.0"
diff --git a/compiler/rustc_lint/src/array_into_iter.rs b/compiler/rustc_lint/src/array_into_iter.rs
index 5ac42c50c7240..1facd97375433 100644
--- a/compiler/rustc_lint/src/array_into_iter.rs
+++ b/compiler/rustc_lint/src/array_into_iter.rs
@@ -13,7 +13,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust
+    /// ```rust,edition2018
     /// # #![allow(unused)]
     /// [1, 2, 3].into_iter().for_each(|n| { *n; });
     /// ```
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index 2850e7a6b44e9..e1bcc3aa52bc6 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -1686,7 +1686,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust
+    /// ```rust,edition2018
     /// let x = 123;
     /// match x {
     ///     0...100 => {}
diff --git a/compiler/rustc_lint/src/non_fmt_panic.rs b/compiler/rustc_lint/src/non_fmt_panic.rs
index 33a6edafa2640..ae9c5ce5c3c2b 100644
--- a/compiler/rustc_lint/src/non_fmt_panic.rs
+++ b/compiler/rustc_lint/src/non_fmt_panic.rs
@@ -18,7 +18,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,no_run
+    /// ```rust,no_run,edition2018
     /// panic!("{}");
     /// panic!(123);
     /// ```
diff --git a/compiler/rustc_lint_defs/Cargo.toml b/compiler/rustc_lint_defs/Cargo.toml
index f9ada5cc95f58..798d50819e2d8 100644
--- a/compiler/rustc_lint_defs/Cargo.toml
+++ b/compiler/rustc_lint_defs/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_lint_defs"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 rustc_ast = { path = "../rustc_ast" }
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index a00561e521357..b14abb9e5db48 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -1584,7 +1584,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust
+    /// ```rust,edition2018
     /// trait Trait { }
     ///
     /// fn takes_trait_object(_: Box<Trait>) {
@@ -3313,7 +3313,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,edition2018,compile_fail
     /// #![deny(rust_2021_prefixes_incompatible_syntax)]
     ///
     /// macro_rules! m {
@@ -3333,6 +3333,8 @@ declare_lint! {
     ///
     /// This lint suggests to add whitespace between the `z` and `"hey"` tokens
     /// to keep them separated in Rust 2021.
+    // Allow this lint -- rustdoc doesn't yet support threading edition into this lint's parser.
+    #[allow(rustdoc::invalid_rust_codeblocks)]
     pub RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
     Allow,
     "identifiers that will be parsed as a prefix in Rust 2021",
diff --git a/compiler/rustc_llvm/Cargo.toml b/compiler/rustc_llvm/Cargo.toml
index 2f0f3dd9ecbb9..d8dfcc84e68da 100644
--- a/compiler/rustc_llvm/Cargo.toml
+++ b/compiler/rustc_llvm/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_llvm"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [features]
 static-libstdcpp = []
diff --git a/compiler/rustc_macros/Cargo.toml b/compiler/rustc_macros/Cargo.toml
index e4dddbab06755..a9192be4d6ef4 100644
--- a/compiler/rustc_macros/Cargo.toml
+++ b/compiler/rustc_macros/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_macros"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 proc-macro = true
diff --git a/compiler/rustc_metadata/Cargo.toml b/compiler/rustc_metadata/Cargo.toml
index 6b874aafa1017..f71fefd179920 100644
--- a/compiler/rustc_metadata/Cargo.toml
+++ b/compiler/rustc_metadata/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_metadata"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_metadata/src/dependency_format.rs b/compiler/rustc_metadata/src/dependency_format.rs
index b8d2256061816..8c41fd9c4a237 100644
--- a/compiler/rustc_metadata/src/dependency_format.rs
+++ b/compiler/rustc_metadata/src/dependency_format.rs
@@ -11,10 +11,10 @@
 //! should be used when linking each output type requested in this session. This
 //! generally follows this set of rules:
 //!
-//!     1. Each library must appear exactly once in the output.
-//!     2. Each rlib contains only one library (it's just an object file)
-//!     3. Each dylib can contain more than one library (due to static linking),
-//!        and can also bring in many dynamic dependencies.
+//! 1. Each library must appear exactly once in the output.
+//! 2. Each rlib contains only one library (it's just an object file)
+//! 3. Each dylib can contain more than one library (due to static linking),
+//!    and can also bring in many dynamic dependencies.
 //!
 //! With these constraints in mind, it's generally a very difficult problem to
 //! find a solution that's not "all rlibs" or "all dylibs". I have suspicions
@@ -22,24 +22,24 @@
 //!
 //! The current selection algorithm below looks mostly similar to:
 //!
-//!     1. If static linking is required, then require all upstream dependencies
-//!        to be available as rlibs. If not, generate an error.
-//!     2. If static linking is requested (generating an executable), then
-//!        attempt to use all upstream dependencies as rlibs. If any are not
-//!        found, bail out and continue to step 3.
-//!     3. Static linking has failed, at least one library must be dynamically
-//!        linked. Apply a heuristic by greedily maximizing the number of
-//!        dynamically linked libraries.
-//!     4. Each upstream dependency available as a dynamic library is
-//!        registered. The dependencies all propagate, adding to a map. It is
-//!        possible for a dylib to add a static library as a dependency, but it
-//!        is illegal for two dylibs to add the same static library as a
-//!        dependency. The same dylib can be added twice. Additionally, it is
-//!        illegal to add a static dependency when it was previously found as a
-//!        dylib (and vice versa)
-//!     5. After all dynamic dependencies have been traversed, re-traverse the
-//!        remaining dependencies and add them statically (if they haven't been
-//!        added already).
+//! 1. If static linking is required, then require all upstream dependencies
+//!    to be available as rlibs. If not, generate an error.
+//! 2. If static linking is requested (generating an executable), then
+//!    attempt to use all upstream dependencies as rlibs. If any are not
+//!    found, bail out and continue to step 3.
+//! 3. Static linking has failed, at least one library must be dynamically
+//!    linked. Apply a heuristic by greedily maximizing the number of
+//!    dynamically linked libraries.
+//! 4. Each upstream dependency available as a dynamic library is
+//!    registered. The dependencies all propagate, adding to a map. It is
+//!    possible for a dylib to add a static library as a dependency, but it
+//!    is illegal for two dylibs to add the same static library as a
+//!    dependency. The same dylib can be added twice. Additionally, it is
+//!    illegal to add a static dependency when it was previously found as a
+//!    dylib (and vice versa)
+//! 5. After all dynamic dependencies have been traversed, re-traverse the
+//!    remaining dependencies and add them statically (if they haven't been
+//!    added already).
 //!
 //! While not perfect, this algorithm should help support use-cases such as leaf
 //! dependencies being static while the larger tree of inner dependencies are
diff --git a/compiler/rustc_middle/Cargo.toml b/compiler/rustc_middle/Cargo.toml
index 68b83fccc85fd..b1fcc34bee1d7 100644
--- a/compiler/rustc_middle/Cargo.toml
+++ b/compiler/rustc_middle/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_middle"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_middle/src/middle/region.rs b/compiler/rustc_middle/src/middle/region.rs
index bd4e83a42ef51..e271f59da8796 100644
--- a/compiler/rustc_middle/src/middle/region.rs
+++ b/compiler/rustc_middle/src/middle/region.rs
@@ -257,7 +257,8 @@ pub struct ScopeTree {
     /// ```
     ///
     /// With the HIR tree (calls numbered for expository purposes)
-    /// ```
+    ///
+    /// ```text
     ///     Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
     /// ```
     ///
diff --git a/compiler/rustc_mir_build/Cargo.toml b/compiler/rustc_mir_build/Cargo.toml
index e9fbc1b186d19..998b80a36c2f7 100644
--- a/compiler/rustc_mir_build/Cargo.toml
+++ b/compiler/rustc_mir_build/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_mir_build"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_mir_dataflow/Cargo.toml b/compiler/rustc_mir_dataflow/Cargo.toml
index 3cd4892402e4c..ffd7e3cd06bd2 100644
--- a/compiler/rustc_mir_dataflow/Cargo.toml
+++ b/compiler/rustc_mir_dataflow/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_mir_dataflow"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_mir_transform/Cargo.toml b/compiler/rustc_mir_transform/Cargo.toml
index 5e1a587b0ecea..bde4e215a2a61 100644
--- a/compiler/rustc_mir_transform/Cargo.toml
+++ b/compiler/rustc_mir_transform/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_mir_transform"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_mir_transform/src/coverage/test_macros/Cargo.toml b/compiler/rustc_mir_transform/src/coverage/test_macros/Cargo.toml
index cc93fd482b5d4..f5e8b65656a3e 100644
--- a/compiler/rustc_mir_transform/src/coverage/test_macros/Cargo.toml
+++ b/compiler/rustc_mir_transform/src/coverage/test_macros/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "coverage_test_macros"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 proc-macro = true
diff --git a/compiler/rustc_monomorphize/Cargo.toml b/compiler/rustc_monomorphize/Cargo.toml
index 350ae08877718..f812afe6b62ba 100644
--- a/compiler/rustc_monomorphize/Cargo.toml
+++ b/compiler/rustc_monomorphize/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_monomorphize"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_parse/Cargo.toml b/compiler/rustc_parse/Cargo.toml
index 1ca1a92252ea4..1decaaa955f02 100644
--- a/compiler/rustc_parse/Cargo.toml
+++ b/compiler/rustc_parse/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_parse"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_parse_format/Cargo.toml b/compiler/rustc_parse_format/Cargo.toml
index 7b77560717e13..aa1714e820f48 100644
--- a/compiler/rustc_parse_format/Cargo.toml
+++ b/compiler/rustc_parse_format/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_parse_format"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 rustc_span = { path = "../rustc_span" }
diff --git a/compiler/rustc_passes/Cargo.toml b/compiler/rustc_passes/Cargo.toml
index bf1e52cd9a8ad..39e578bce7ef6 100644
--- a/compiler/rustc_passes/Cargo.toml
+++ b/compiler/rustc_passes/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_passes"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 tracing = "0.1"
diff --git a/compiler/rustc_plugin_impl/Cargo.toml b/compiler/rustc_plugin_impl/Cargo.toml
index c8eaca0703cb5..4e666e7e93d53 100644
--- a/compiler/rustc_plugin_impl/Cargo.toml
+++ b/compiler/rustc_plugin_impl/Cargo.toml
@@ -2,7 +2,7 @@
 name = "rustc_plugin_impl"
 version = "0.0.0"
 build = false
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_privacy/Cargo.toml b/compiler/rustc_privacy/Cargo.toml
index 6ac2915c34526..d952e288a6477 100644
--- a/compiler/rustc_privacy/Cargo.toml
+++ b/compiler/rustc_privacy/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_privacy"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 rustc_middle = { path = "../rustc_middle" }
diff --git a/compiler/rustc_query_impl/Cargo.toml b/compiler/rustc_query_impl/Cargo.toml
index 7c8dbe34240e2..89df3d4674b6b 100644
--- a/compiler/rustc_query_impl/Cargo.toml
+++ b/compiler/rustc_query_impl/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_query_impl"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_query_system/Cargo.toml b/compiler/rustc_query_system/Cargo.toml
index 47fb78be64079..11c18a497e5e6 100644
--- a/compiler/rustc_query_system/Cargo.toml
+++ b/compiler/rustc_query_system/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_query_system"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_resolve/Cargo.toml b/compiler/rustc_resolve/Cargo.toml
index 1581b0562752e..f1d3315d6e66a 100644
--- a/compiler/rustc_resolve/Cargo.toml
+++ b/compiler/rustc_resolve/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_resolve"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 test = false
diff --git a/compiler/rustc_save_analysis/Cargo.toml b/compiler/rustc_save_analysis/Cargo.toml
index 535a48bcda182..15a89d82fa696 100644
--- a/compiler/rustc_save_analysis/Cargo.toml
+++ b/compiler/rustc_save_analysis/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_save_analysis"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 tracing = "0.1"
diff --git a/compiler/rustc_serialize/Cargo.toml b/compiler/rustc_serialize/Cargo.toml
index 593a7563e36a2..49778f82253bf 100644
--- a/compiler/rustc_serialize/Cargo.toml
+++ b/compiler/rustc_serialize/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_serialize"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 indexmap = "1"
diff --git a/compiler/rustc_session/Cargo.toml b/compiler/rustc_session/Cargo.toml
index 5b617a2997cd6..4cff21bee3dc3 100644
--- a/compiler/rustc_session/Cargo.toml
+++ b/compiler/rustc_session/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_session"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 getopts = "0.2"
diff --git a/compiler/rustc_span/Cargo.toml b/compiler/rustc_span/Cargo.toml
index e475e89d87e8e..781fb8c1e5d8c 100644
--- a/compiler/rustc_span/Cargo.toml
+++ b/compiler/rustc_span/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_span"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_symbol_mangling/Cargo.toml b/compiler/rustc_symbol_mangling/Cargo.toml
index aebf77a1fd85f..d5befa10e2363 100644
--- a/compiler/rustc_symbol_mangling/Cargo.toml
+++ b/compiler/rustc_symbol_mangling/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_symbol_mangling"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_target/Cargo.toml b/compiler/rustc_target/Cargo.toml
index e47a84dbc117e..925813e6bb427 100644
--- a/compiler/rustc_target/Cargo.toml
+++ b/compiler/rustc_target/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_target"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 bitflags = "1.2.1"
diff --git a/compiler/rustc_trait_selection/Cargo.toml b/compiler/rustc_trait_selection/Cargo.toml
index e2c626d1b2207..9a9737362c6c8 100644
--- a/compiler/rustc_trait_selection/Cargo.toml
+++ b/compiler/rustc_trait_selection/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_trait_selection"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
index c8bcab6efd7ca..2ecc169e1cf1d 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
@@ -104,19 +104,21 @@ impl ChildrenExt for Children {
                 let self_ty = trait_ref.self_ty();
 
                 // FIXME: should postpone string formatting until we decide to actually emit.
-                with_no_trimmed_paths(|| OverlapError {
-                    with_impl: possible_sibling,
-                    trait_desc: trait_ref.print_only_trait_path().to_string(),
-                    // Only report the `Self` type if it has at least
-                    // some outer concrete shell; otherwise, it's
-                    // not adding much information.
-                    self_desc: if self_ty.has_concrete_skeleton() {
-                        Some(self_ty.to_string())
-                    } else {
-                        None
-                    },
-                    intercrate_ambiguity_causes: overlap.intercrate_ambiguity_causes,
-                    involves_placeholder: overlap.involves_placeholder,
+                with_no_trimmed_paths(|| {
+                    OverlapError {
+                        with_impl: possible_sibling,
+                        trait_desc: trait_ref.print_only_trait_path().to_string(),
+                        // Only report the `Self` type if it has at least
+                        // some outer concrete shell; otherwise, it's
+                        // not adding much information.
+                        self_desc: if self_ty.has_concrete_skeleton() {
+                            Some(self_ty.to_string())
+                        } else {
+                            None
+                        },
+                        intercrate_ambiguity_causes: overlap.intercrate_ambiguity_causes,
+                        involves_placeholder: overlap.involves_placeholder,
+                    }
                 })
             };
 
diff --git a/compiler/rustc_traits/Cargo.toml b/compiler/rustc_traits/Cargo.toml
index 219165ff55035..2e56a1bf6839e 100644
--- a/compiler/rustc_traits/Cargo.toml
+++ b/compiler/rustc_traits/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_traits"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 tracing = "0.1"
diff --git a/compiler/rustc_ty_utils/Cargo.toml b/compiler/rustc_ty_utils/Cargo.toml
index 2eb27fb1ad67e..78df95e680e00 100644
--- a/compiler/rustc_ty_utils/Cargo.toml
+++ b/compiler/rustc_ty_utils/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_ty_utils"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 tracing = "0.1"
diff --git a/compiler/rustc_type_ir/Cargo.toml b/compiler/rustc_type_ir/Cargo.toml
index 1f6acbe0d811d..439e6cdf70698 100644
--- a/compiler/rustc_type_ir/Cargo.toml
+++ b/compiler/rustc_type_ir/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_type_ir"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 doctest = false
diff --git a/compiler/rustc_typeck/Cargo.toml b/compiler/rustc_typeck/Cargo.toml
index dd76a5e4b99b2..7e570e151c529 100644
--- a/compiler/rustc_typeck/Cargo.toml
+++ b/compiler/rustc_typeck/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_typeck"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 test = false
diff --git a/compiler/rustc_typeck/src/astconv/mod.rs b/compiler/rustc_typeck/src/astconv/mod.rs
index 2f2223ee822e4..33df541eb2ba8 100644
--- a/compiler/rustc_typeck/src/astconv/mod.rs
+++ b/compiler/rustc_typeck/src/astconv/mod.rs
@@ -2417,13 +2417,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
             if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
                 // Our own parameters are the resolved lifetimes.
-                match param.kind {
-                    GenericParamDefKind::Lifetime
-                        if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] =>
-                    {
+                if let GenericParamDefKind::Lifetime = param.kind {
+                    if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
                         self.ast_region_to_region(lifetime, None).into()
+                    } else {
+                        bug!()
                     }
-                    _ => bug!(),
+                } else {
+                    bug!()
                 }
             } else {
                 match param.kind {
diff --git a/src/bootstrap/Cargo.toml b/src/bootstrap/Cargo.toml
index 0b76a13e02b77..1ce1f0b26db58 100644
--- a/src/bootstrap/Cargo.toml
+++ b/src/bootstrap/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "bootstrap"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 build = "build.rs"
 
 [lib]
diff --git a/src/bootstrap/check.rs b/src/bootstrap/check.rs
index f5fad4b413684..f66f282bea933 100644
--- a/src/bootstrap/check.rs
+++ b/src/bootstrap/check.rs
@@ -262,7 +262,7 @@ impl Step for CodegenBackend {
         let mut cargo = builder.cargo(
             compiler,
             Mode::Codegen,
-            SourceType::Submodule,
+            SourceType::InTree,
             target,
             cargo_subcommand(builder.kind),
         );
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index df9e9bce41527..ae234fb1dc729 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -817,8 +817,7 @@ impl Step for CodegenBackend {
 
         let out_dir = builder.cargo_out(compiler, Mode::Codegen, target);
 
-        let mut cargo =
-            builder.cargo(compiler, Mode::Codegen, SourceType::Submodule, target, "build");
+        let mut cargo = builder.cargo(compiler, Mode::Codegen, SourceType::InTree, target, "build");
         cargo
             .arg("--manifest-path")
             .arg(builder.src.join(format!("compiler/rustc_codegen_{}/Cargo.toml", backend)));
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 386ffb384a81e..272b715311137 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -390,7 +390,7 @@ impl Step for Rustfmt {
             host,
             "test",
             "src/tools/rustfmt",
-            SourceType::Submodule,
+            SourceType::InTree,
             &[],
         );
 
diff --git a/src/build_helper/Cargo.toml b/src/build_helper/Cargo.toml
index 17a9e55b3238c..d88df0e08fab3 100644
--- a/src/build_helper/Cargo.toml
+++ b/src/build_helper/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "build_helper"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 path = "lib.rs"
diff --git a/src/etc/test-float-parse/Cargo.toml b/src/etc/test-float-parse/Cargo.toml
index 8226e815c2c1e..7ee19a0b6d913 100644
--- a/src/etc/test-float-parse/Cargo.toml
+++ b/src/etc/test-float-parse/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "test-float-parse"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 publish = false
 
 [workspace]
diff --git a/src/librustdoc/Cargo.toml b/src/librustdoc/Cargo.toml
index e02cef235ae00..945b2a8e9a80e 100644
--- a/src/librustdoc/Cargo.toml
+++ b/src/librustdoc/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustdoc"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 path = "lib.rs"
diff --git a/src/rustdoc-json-types/Cargo.toml b/src/rustdoc-json-types/Cargo.toml
index a692f6f896da7..d60699efd36cb 100644
--- a/src/rustdoc-json-types/Cargo.toml
+++ b/src/rustdoc-json-types/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustdoc-json-types"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [lib]
 path = "lib.rs"
diff --git a/src/tools/build-manifest/Cargo.toml b/src/tools/build-manifest/Cargo.toml
index 334407c2b2e56..340acff34f2ab 100644
--- a/src/tools/build-manifest/Cargo.toml
+++ b/src/tools/build-manifest/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "build-manifest"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 toml = "0.5"
diff --git a/src/tools/bump-stage0/Cargo.toml b/src/tools/bump-stage0/Cargo.toml
index 7d64e20a3d360..cf8840ff6ee89 100644
--- a/src/tools/bump-stage0/Cargo.toml
+++ b/src/tools/bump-stage0/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "bump-stage0"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
diff --git a/src/tools/cargotest/Cargo.toml b/src/tools/cargotest/Cargo.toml
index a88272d234456..bfd894e2bd27b 100644
--- a/src/tools/cargotest/Cargo.toml
+++ b/src/tools/cargotest/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "cargotest2"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [[bin]]
 name = "cargotest"
diff --git a/src/tools/compiletest/Cargo.toml b/src/tools/compiletest/Cargo.toml
index d6aa3fd2631f5..e9426a2d9f58c 100644
--- a/src/tools/compiletest/Cargo.toml
+++ b/src/tools/compiletest/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "compiletest"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 colored = "2"
diff --git a/src/tools/error_index_generator/Cargo.toml b/src/tools/error_index_generator/Cargo.toml
index 2e4b7beb37601..c84b79e11e9b4 100644
--- a/src/tools/error_index_generator/Cargo.toml
+++ b/src/tools/error_index_generator/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "error_index_generator"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 rustdoc = { path = "../../librustdoc" }
diff --git a/src/tools/expand-yaml-anchors/Cargo.toml b/src/tools/expand-yaml-anchors/Cargo.toml
index 358dff0653292..9a25b6c1f1c87 100644
--- a/src/tools/expand-yaml-anchors/Cargo.toml
+++ b/src/tools/expand-yaml-anchors/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "expand-yaml-anchors"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 yaml-rust = "0.4.3"
diff --git a/src/tools/html-checker/Cargo.toml b/src/tools/html-checker/Cargo.toml
index e88d2f0d928fb..34d3954db28dc 100644
--- a/src/tools/html-checker/Cargo.toml
+++ b/src/tools/html-checker/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "html-checker"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [[bin]]
 name = "html-checker"
diff --git a/src/tools/jsondocck/Cargo.toml b/src/tools/jsondocck/Cargo.toml
index a65deb1254168..ccabe6483d7a4 100644
--- a/src/tools/jsondocck/Cargo.toml
+++ b/src/tools/jsondocck/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "jsondocck"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 jsonpath_lib = "0.2"
diff --git a/src/tools/linkchecker/Cargo.toml b/src/tools/linkchecker/Cargo.toml
index 21ba226955646..1d8f2f918823f 100644
--- a/src/tools/linkchecker/Cargo.toml
+++ b/src/tools/linkchecker/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "linkchecker"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [[bin]]
 name = "linkchecker"
diff --git a/src/tools/lint-docs/Cargo.toml b/src/tools/lint-docs/Cargo.toml
index 6792887fa5d71..3578bda8276e7 100644
--- a/src/tools/lint-docs/Cargo.toml
+++ b/src/tools/lint-docs/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "lint-docs"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 description = "A script to extract the lint documentation for the rustc book."
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
diff --git a/src/tools/lint-docs/src/lib.rs b/src/tools/lint-docs/src/lib.rs
index e5c7f12571238..fdc89a184da52 100644
--- a/src/tools/lint-docs/src/lib.rs
+++ b/src/tools/lint-docs/src/lib.rs
@@ -149,6 +149,10 @@ impl<'a> LintExtractor<'a> {
                         } else if line.starts_with("// ") {
                             // Ignore comments.
                             continue;
+                        } else if line.starts_with("#[allow") {
+                            // Ignore allow of lints (useful for
+                            // invalid_rust_codeblocks).
+                            continue;
                         } else {
                             let name = lint_name(line).map_err(|e| {
                                 format!(
diff --git a/src/tools/remote-test-client/Cargo.toml b/src/tools/remote-test-client/Cargo.toml
index 7b20ba83546be..d59cd6b3d8e22 100644
--- a/src/tools/remote-test-client/Cargo.toml
+++ b/src/tools/remote-test-client/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "remote-test-client"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
diff --git a/src/tools/remote-test-server/Cargo.toml b/src/tools/remote-test-server/Cargo.toml
index 01309aec9a338..e6be8530cf635 100644
--- a/src/tools/remote-test-server/Cargo.toml
+++ b/src/tools/remote-test-server/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "remote-test-server"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
diff --git a/src/tools/rust-demangler/Cargo.toml b/src/tools/rust-demangler/Cargo.toml
index 157409bc8472c..2bb73b3262d8d 100644
--- a/src/tools/rust-demangler/Cargo.toml
+++ b/src/tools/rust-demangler/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rust-demangler"
 version = "0.0.1"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 regex = "1.0"
diff --git a/src/tools/rustbook/Cargo.toml b/src/tools/rustbook/Cargo.toml
index da36ce0e69002..de1327d74ff57 100644
--- a/src/tools/rustbook/Cargo.toml
+++ b/src/tools/rustbook/Cargo.toml
@@ -2,7 +2,7 @@
 name = "rustbook"
 version = "0.1.0"
 license = "MIT OR Apache-2.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 clap = "2.25.0"
diff --git a/src/tools/rustc-workspace-hack/Cargo.toml b/src/tools/rustc-workspace-hack/Cargo.toml
index 38b9fefbaf576..a28cf28841e54 100644
--- a/src/tools/rustc-workspace-hack/Cargo.toml
+++ b/src/tools/rustc-workspace-hack/Cargo.toml
@@ -5,7 +5,7 @@ license = 'MIT OR Apache-2.0'
 description = """
 Hack for the compiler's own build system
 """
-edition = "2018"
+edition = "2021"
 
 [lib]
 path = "lib.rs"
diff --git a/src/tools/rustdoc-themes/Cargo.toml b/src/tools/rustdoc-themes/Cargo.toml
index 4b2ad982a84fb..3d8c77d36d70d 100644
--- a/src/tools/rustdoc-themes/Cargo.toml
+++ b/src/tools/rustdoc-themes/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustdoc-themes"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 [[bin]]
 name = "rustdoc-themes"
diff --git a/src/tools/rustdoc/Cargo.toml b/src/tools/rustdoc/Cargo.toml
index 5625707b25a53..c4101f72cc2da 100644
--- a/src/tools/rustdoc/Cargo.toml
+++ b/src/tools/rustdoc/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustdoc-tool"
 version = "0.0.0"
-edition = "2018"
+edition = "2021"
 
 # Cargo adds a number of paths to the dylib search path on windows, which results in
 # the wrong rustdoc being executed. To avoid the conflicting rustdocs, we name the "tool"
diff --git a/src/tools/rustfmt/Cargo.toml b/src/tools/rustfmt/Cargo.toml
index 81e3e26e8b000..7b4667c17c864 100644
--- a/src/tools/rustfmt/Cargo.toml
+++ b/src/tools/rustfmt/Cargo.toml
@@ -8,7 +8,7 @@ readme = "README.md"
 license = "Apache-2.0/MIT"
 build = "build.rs"
 categories = ["development-tools"]
-edition = "2018"
+edition = "2021"
 
 [[bin]]
 name = "rustfmt"
diff --git a/src/tools/tidy/Cargo.toml b/src/tools/tidy/Cargo.toml
index 57fe5a62e9aa7..69c8063f42e26 100644
--- a/src/tools/tidy/Cargo.toml
+++ b/src/tools/tidy/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "tidy"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 autobins = false
 
 [dependencies]
diff --git a/src/tools/tidy/src/edition.rs b/src/tools/tidy/src/edition.rs
index 283c43e325c05..b5e9ceddbafd1 100644
--- a/src/tools/tidy/src/edition.rs
+++ b/src/tools/tidy/src/edition.rs
@@ -1,10 +1,15 @@
-//! Tidy check to ensure that crate `edition` is '2018'
+//! Tidy check to ensure that crate `edition` is '2018' or '2021'.
 
 use std::path::Path;
 
 fn is_edition_2018(mut line: &str) -> bool {
     line = line.trim();
-    line == "edition = \"2018\"" || line == "edition = \'2018\'"
+    line == "edition = \"2018\""
+}
+
+fn is_edition_2021(mut line: &str) -> bool {
+    line = line.trim();
+    line == "edition = \"2021\""
 }
 
 pub fn check(path: &Path, bad: &mut bool) {
@@ -13,17 +18,38 @@ pub fn check(path: &Path, bad: &mut bool) {
         &mut |path| super::filter_dirs(path) || path.ends_with("src/test"),
         &mut |entry, contents| {
             let file = entry.path();
+            let filestr = file.to_string_lossy().replace("\\", "/");
             let filename = file.file_name().unwrap();
             if filename != "Cargo.toml" {
                 return;
             }
-            let has_edition = contents.lines().any(is_edition_2018);
-            if !has_edition {
-                tidy_error!(
-                    bad,
-                    "{} doesn't have `edition = \"2018\"` on a separate line",
-                    file.display()
-                );
+
+            // Library crates are not yet ready to migrate to 2021.
+            //
+            // The reference and rustc-dev-guide are submodules, so are left at
+            // 2018 for now. They should be removed from this exception list
+            // when bumped.
+            if path.components().any(|c| c.as_os_str() == "library")
+                || filestr.contains("src/doc/reference/style-check/Cargo.toml")
+                || filestr.contains("src/doc/rustc-dev-guide/ci/date-check/Cargo.toml")
+            {
+                let has = contents.lines().any(is_edition_2018);
+                if !has {
+                    tidy_error!(
+                        bad,
+                        "{} doesn't have `edition = \"2018\"` on a separate line",
+                        file.display()
+                    );
+                }
+            } else {
+                let is_2021 = contents.lines().any(is_edition_2021);
+                if !is_2021 {
+                    tidy_error!(
+                        bad,
+                        "{} doesn't have `edition = \"2021\"` on a separate line",
+                        file.display()
+                    );
+                }
             }
         },
     );
diff --git a/src/tools/tier-check/Cargo.toml b/src/tools/tier-check/Cargo.toml
index d6119cac5f39e..3f08165a3fc63 100644
--- a/src/tools/tier-check/Cargo.toml
+++ b/src/tools/tier-check/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "tier-check"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 license = "MIT OR Apache-2.0"
 
 [dependencies]
diff --git a/src/tools/unicode-table-generator/Cargo.toml b/src/tools/unicode-table-generator/Cargo.toml
index 948773f7810c3..ef01877c0b94b 100644
--- a/src/tools/unicode-table-generator/Cargo.toml
+++ b/src/tools/unicode-table-generator/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "unicode-bdd"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
diff --git a/src/tools/unstable-book-gen/Cargo.toml b/src/tools/unstable-book-gen/Cargo.toml
index febeaa446b394..73e5a91bec70a 100644
--- a/src/tools/unstable-book-gen/Cargo.toml
+++ b/src/tools/unstable-book-gen/Cargo.toml
@@ -2,7 +2,7 @@
 name = "unstable-book-gen"
 version = "0.1.0"
 license = "MIT OR Apache-2.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 tidy = { path = "../tidy" }
diff --git a/src/tools/x/Cargo.toml b/src/tools/x/Cargo.toml
index 264a741159a8a..3150272796234 100644
--- a/src/tools/x/Cargo.toml
+++ b/src/tools/x/Cargo.toml
@@ -2,5 +2,5 @@
 name = "x"
 version = "0.1.0"
 description = "Run x.py slightly more conveniently"
-edition = "2018"
+edition = "2021"
 publish = false