Downgrade linker-warnings to allow-by-default

compiler/rustc_lint_defs/src/builtin.rs

@@ -4091,6 +4091,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust,ignore (needs CLI args, platform-specific)
+    /// #[warn(linker_messages)]
     /// extern "C" {
     ///   fn foo();
     /// }
@@ -4104,17 +4105,24 @@ declare_lint! {
     ///          >>> referenced by rust_out.69edbd30df4ae57d-cgu.0
     ///          >>>               rust_out.rust_out.69edbd30df4ae57d-cgu.0.rcgu.o:(rust_out::main::h3a90094b06757803)
     ///   |
-    ///   = note: `#[warn(linker_messages)]` on by default
-    ///
+    /// note: the lint level is defined here
+    ///  --> warn.rs:1:9
+    ///   |
+    /// 1 | #![warn(linker_messages)]
+    ///   |         ^^^^^^^^^^^^^^^
     /// warning: 1 warning emitted
     /// ```
     ///
     /// ### Explanation
     ///
-    /// Linkers emit platform-specific and program-specific warnings that cannot be predicted in advance by the rust compiler.
-    /// They are forwarded by default, but can be disabled by adding `#![allow(linker_messages)]` at the crate root.
+    /// Linkers emit platform-specific and program-specific warnings that cannot be predicted in
+    /// advance by the Rust compiler. Such messages are ignored by default for now. While linker
+    /// warnings could be very useful they have been ignored for many years by essentially all
+    /// users, so we need to do a bit more work than just surfacing their text to produce a clear
+    /// and actionable warning of similar quality to our other diagnostics. See this tracking
+    /// issue for more details: <https://github.com/rust-lang/rust/issues/136096>.
     pub LINKER_MESSAGES,
-    Warn,
+    Allow,
     "warnings emitted at runtime by the target-specific linker program"
 }
 

tests/run-make/linker-warning/rmake.rs

@@ -8,6 +8,7 @@ fn run_rustc() -> Rustc {
         // Make sure we use a consistent value.
         .arg("-Clink-self-contained=-linker")
         .arg("-Zunstable-options")
+        .arg("-Wlinker-messages")
         .output("main")
         .linker("./fake-linker");
     if run_make_support::target() == "x86_64-unknown-linux-gnu" {

tests/run-make/rust-lld-by-default-beta-stable/rmake.rs

@@ -12,7 +12,7 @@ use run_make_support::rustc;
 fn main() {
     // A regular compilation should not use rust-lld by default. We'll check that by asking the
     // linker to display its version number with a link-arg.
-    let output = rustc().link_arg("-Wl,-v").input("main.rs").run();
+    let output = rustc().arg("-Wlinker-messages").link_arg("-Wl,-v").input("main.rs").run();
     assert!(
         !find_lld_version_in_logs(output.stderr_utf8()),
         "the LLD version string should not be present in the output logs:\n{}",

tests/run-make/rust-lld-by-default-nightly/rmake.rs

@@ -12,15 +12,20 @@ use run_make_support::rustc;
 fn main() {
     // A regular compilation should use rust-lld by default. We'll check that by asking the linker
     // to display its version number with a link-arg.
-    let output = rustc().link_arg("-Wl,-v").input("main.rs").run();
+    let output = rustc().arg("-Wlinker-messages").link_arg("-Wl,-v").input("main.rs").run();
     assert!(
         find_lld_version_in_logs(output.stderr_utf8()),
         "the LLD version string should be present in the output logs:\n{}",
         output.stderr_utf8()
     );
 
     // But it can still be disabled by turning the linker feature off.
-    let output = rustc().link_arg("-Wl,-v").arg("-Zlinker-features=-lld").input("main.rs").run();
+    let output = rustc()
+        .arg("-Wlinker-messages")
+        .link_arg("-Wl,-v")
+        .arg("-Zlinker-features=-lld")
+        .input("main.rs")
+        .run();
     assert!(
         !find_lld_version_in_logs(output.stderr_utf8()),
         "the LLD version string should not be present in the output logs:\n{}",

tests/run-make/rust-lld-custom-target/rmake.rs

@@ -16,6 +16,7 @@ fn main() {
     // the linker to display its version number with a link-arg.
     let output = rustc()
         .crate_type("cdylib")
+        .arg("-Wlinker-messages")
         .target("custom-target.json")
         .link_arg("-Wl,-v")
         .input("lib.rs")
@@ -29,6 +30,7 @@ fn main() {
     // But it can also be disabled via linker features.
     let output = rustc()
         .crate_type("cdylib")
+        .arg("-Wlinker-messages")
         .target("custom-target.json")
         .arg("-Zlinker-features=-lld")
         .link_arg("-Wl,-v")

tests/run-make/rust-lld/rmake.rs

@@ -17,6 +17,7 @@ fn main() {
         .arg("-Zlinker-features=+lld")
         .arg("-Clink-self-contained=+linker")
         .arg("-Zunstable-options")
+        .arg("-Wlinker-messages")
         .link_arg(linker_version_flag)
         .input("main.rs")
         .run();
@@ -27,8 +28,12 @@ fn main() {
     );
 
     // It should not be used when we explicitly opt-out of lld.
-    let output =
-        rustc().link_arg(linker_version_flag).arg("-Zlinker-features=-lld").input("main.rs").run();
+    let output = rustc()
+        .link_arg(linker_version_flag)
+        .arg("-Zlinker-features=-lld")
+        .arg("-Wlinker-messages")
+        .input("main.rs")
+        .run();
     assert!(
         !find_lld_version_in_logs(output.stderr_utf8()),
         "the LLD version string should not be present in the output logs:\n{}",
@@ -44,6 +49,7 @@ fn main() {
         .arg("-Zlinker-features=-lld")
         .arg("-Zlinker-features=+lld")
         .arg("-Zlinker-features=-lld,+lld")
+        .arg("-Wlinker-messages")
         .input("main.rs")
         .run();
     assert!(