Fixes #9677 - Lint against mod lib;

CHANGELOG.md

@@ -4055,6 +4055,7 @@ Released 2018-09-13
 [`mistyped_literal_suffixes`]: https://rust-lang.github.io/rust-clippy/master/index.html#mistyped_literal_suffixes
 [`mixed_case_hex_literals`]: https://rust-lang.github.io/rust-clippy/master/index.html#mixed_case_hex_literals
 [`mixed_read_write_in_expression`]: https://rust-lang.github.io/rust-clippy/master/index.html#mixed_read_write_in_expression
+[`mod_lib`]: https://rust-lang.github.io/rust-clippy/master/index.html#mod_lib
 [`mod_module_files`]: https://rust-lang.github.io/rust-clippy/master/index.html#mod_module_files
 [`module_inception`]: https://rust-lang.github.io/rust-clippy/master/index.html#module_inception
 [`module_name_repetitions`]: https://rust-lang.github.io/rust-clippy/master/index.html#module_name_repetitions

clippy_lints/src/lib.rs

@@ -192,6 +192,7 @@ mod missing_enforced_import_rename;
 mod missing_inline;
 mod missing_trait_methods;
 mod mixed_read_write_in_expression;
+mod mod_lib;
 mod module_style;
 mod multi_assignments;
 mod mut_key;
@@ -912,6 +913,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_early_pass(|| Box::new(partial_pub_fields::PartialPubFields));
     store.register_late_pass(|_| Box::new(missing_trait_methods::MissingTraitMethods));
     store.register_late_pass(|_| Box::new(from_raw_with_void_ptr::FromRawWithVoidPtr));
+    store.register_late_pass(|_| Box::new(mod_lib::ModLib));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/mod_lib.rs

@@ -0,0 +1,46 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use rustc_hir::{Item, ItemKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::sym;
+
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// ### Why is this bad?
+    ///
+    /// ### Example
+    /// ```rust
+    /// // example code where clippy issues a warning
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// // example code which does not raise clippy warning
+    /// ```
+    #[clippy::version = "1.66.0"]
+    pub MOD_LIB,
+    pedantic,
+    "default lint description"
+}
+
+#[derive(Default)]
+pub struct ModLib;
+
+impl_lint_pass!(ModLib => [MOD_LIB]);
+
+impl<'tcx> LateLintPass<'tcx> for ModLib {
+    fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
+        if let ItemKind::Mod(_) = item.kind {
+            if item.ident.name == sym::lib {
+                span_lint_and_help(
+                    cx,
+                    MOD_LIB,
+                    item.span,
+                    "uncommon use of mod::lib",
+                    None,
+                    "you probably meant use::package instead",
+                );
+            }
+        }
+    }
+}

src/docs/mod_lib.txt

@@ -0,0 +1,12 @@
+### What it does
+
+### Why is this bad?
+
+### Example
+```
+// example code where clippy issues a warning
+```
+Use instead:
+```
+// example code which does not raise clippy warning
+```

tests/ui/mod_lib/lib.rs

@@ -0,0 +1,3 @@
+pub fn something() -> i32 {
+    42
+}

tests/ui/mod_lib/lib.stderr

@@ -0,0 +1,9 @@
+error[E0601]: `main` function not found in crate `lib`
+  --> $DIR/lib.rs:3:2
+   |
+LL | }
+   |  ^ consider adding a `main` function to `$DIR/lib.rs`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0601`.

tests/ui/mod_lib/main.rs

@@ -0,0 +1,8 @@
+#![allow(unused)]
+#![warn(clippy::mod_lib)]
+
+mod lib;
+
+fn main() {
+    println!("{}", lib::something());
+}

tests/ui/mod_lib/main.stderr

@@ -0,0 +1,20 @@
+error: unknown lint: `clippy::mod_lib`
+  --> $DIR/main.rs:2:9
+   |
+LL | #![warn(clippy::mod_lib)]
+   |         ^^^^^^^^^^^^^^^ help: did you mean: `clippy::min_max`
+   |
+   = note: `-D unknown-lints` implied by `-D warnings`
+
+error: found module declaration for lib.rs
+  --> $DIR/main.rs:4:1
+   |
+LL | mod lib;
+   | ^^^^^^^^
+   |
+   = note: lib.rs is the root of this crate's library target
+   = help: to refer to it from other targets, use the library's name as the path
+   = note: `-D special-module-name` implied by `-D warnings`
+
+error: aborting due to 2 previous errors
+