From 37d7d36a51f72aff88b95ff699b1cf3d85e1b22a Mon Sep 17 00:00:00 2001
From: yukang <moorekang@gmail.com>
Date: Sun, 12 Oct 2025 13:39:08 +0800
Subject: [PATCH] uplift module inspect

---
 compiler/rustc_hir/src/intravisit.rs          |  1 +
 compiler/rustc_hir_analysis/src/check/mod.rs  |  2 +
 compiler/rustc_lint/src/late.rs               | 36 ++++----
 compiler/rustc_lint/src/lib.rs                | 13 +++
 compiler/rustc_lint/src/module_inception.rs   | 92 +++++++++++++++++++
 library/core/src/async_iter/mod.rs            |  1 +
 library/core/src/future/mod.rs                |  1 +
 library/std/src/sys/process/unix/mod.rs       |  1 +
 library/test/src/lib.rs                       |  1 +
 src/bootstrap/src/core/config/mod.rs          |  2 +-
 tests/ui/expr/weird-exprs.rs                  |  1 +
 tests/ui/imports/issue-62767.rs               |  1 +
 tests/ui/lint/module-inception-allow.rs       | 24 +++++
 .../convoluted-locals-131474-with-mods.rs     |  1 +
 .../ui/lint/non-local-defs/module_as_local.rs |  1 +
 tests/ui/structs-enums/rec-align-u64.rs       |  2 +
 16 files changed, 159 insertions(+), 21 deletions(-)
 create mode 100644 compiler/rustc_lint/src/module_inception.rs
 create mode 100644 tests/ui/lint/module-inception-allow.rs

diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index eb682f32111a5..2540f1ebf02e1 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -529,6 +529,7 @@ pub fn walk_param<'v, V: Visitor<'v>>(visitor: &mut V, param: &'v Param<'v>) ->
 
 pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item<'v>) -> V::Result {
     let Item { owner_id: _, kind, span: _, vis_span: _, has_delayed_lints: _ } = item;
+
     try_visit!(visitor.visit_id(item.hir_id()));
     match *kind {
         ItemKind::ExternCrate(orig_name, ident) => {
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index 0166c3b980de3..648d3166e32ac 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -63,6 +63,8 @@ a type parameter).
 */
 
 pub mod always_applicable;
+#[cfg_attr(bootstrap, allow(unknown_lints))]
+#[allow(module_inception)]
 mod check;
 mod compare_impl_item;
 mod entry;
diff --git a/compiler/rustc_lint/src/late.rs b/compiler/rustc_lint/src/late.rs
index ccfba715a1be3..ab38e0c340c23 100644
--- a/compiler/rustc_lint/src/late.rs
+++ b/compiler/rustc_lint/src/late.rs
@@ -405,14 +405,6 @@ fn late_lint_mod_inner<'tcx, T: LateLintPass<'tcx>>(
 }
 
 fn late_lint_crate<'tcx>(tcx: TyCtxt<'tcx>) {
-    // Note: `passes` is often empty.
-    let passes: Vec<_> =
-        unerased_lint_store(tcx.sess).late_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
-
-    if passes.is_empty() {
-        return;
-    }
-
     let context = LateContext {
         tcx,
         enclosing_body: None,
@@ -426,19 +418,23 @@ fn late_lint_crate<'tcx>(tcx: TyCtxt<'tcx>) {
 
     let lints_that_dont_need_to_run = tcx.lints_that_dont_need_to_run(());
 
-    let mut filtered_passes: Vec<Box<dyn LateLintPass<'tcx>>> = passes
-        .into_iter()
-        .filter(|pass| {
-            let lints = (**pass).get_lints();
-            // Lintless passes are always in
-            lints.is_empty() ||
-            // If the pass doesn't have a single needed lint, omit it
-            !lints.iter().all(|lint| lints_that_dont_need_to_run.contains(&LintId::of(lint)))
-        })
-        .collect();
+    let mut passes: Vec<Box<dyn LateLintPass<'tcx>>> =
+        vec![Box::new(crate::BuiltinCombinedLateLintPass::new()), Box::new(HardwiredLints)];
+
+    // Filter out passes whose lints are all in the "don't need to run" set
+    passes.retain(|pass| {
+        let lints = (**pass).get_lints();
+        // Lintless passes are always in
+        lints.is_empty() ||
+        // If the pass doesn't have a single needed lint, omit it
+        !lints.iter().all(|lint| lints_that_dont_need_to_run.contains(&LintId::of(lint)))
+    });
+
+    if passes.is_empty() {
+        return;
+    }
 
-    filtered_passes.push(Box::new(HardwiredLints));
-    let pass = RuntimeCombinedLateLintPass { passes: &mut filtered_passes[..] };
+    let pass = RuntimeCombinedLateLintPass { passes: &mut passes };
     late_lint_crate_inner(tcx, context, pass);
 }
 
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 9bb53fea54a18..abad9447fa0a5 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -59,6 +59,7 @@ pub mod lifetime_syntax;
 mod lints;
 mod macro_expr_fragment_specifier_2024_migration;
 mod map_unit_fn;
+mod module_inception;
 mod multiple_supertrait_upcastable;
 mod non_ascii_idents;
 mod non_fmt_panic;
@@ -100,6 +101,7 @@ use let_underscore::*;
 use lifetime_syntax::*;
 use macro_expr_fragment_specifier_2024_migration::*;
 use map_unit_fn::*;
+use module_inception::*;
 use multiple_supertrait_upcastable::*;
 use non_ascii_idents::*;
 use non_fmt_panic::NonPanicFmt;
@@ -185,6 +187,16 @@ early_lint_methods!(
     ]
 );
 
+late_lint_methods!(
+    declare_combined_late_lint_pass,
+    [
+        BuiltinCombinedLateLintPass,
+        [
+            ModuleInception: ModuleInception::new(),
+        ]
+    ]
+);
+
 late_lint_methods!(
     declare_combined_late_lint_pass,
     [
@@ -273,6 +285,7 @@ fn register_builtins(store: &mut LintStore) {
 
     store.register_lints(&BuiltinCombinedPreExpansionLintPass::get_lints());
     store.register_lints(&BuiltinCombinedEarlyLintPass::get_lints());
+    store.register_lints(&BuiltinCombinedLateLintPass::get_lints());
     store.register_lints(&BuiltinCombinedModuleLateLintPass::get_lints());
     store.register_lints(&foreign_modules::get_lints());
     store.register_lints(&HardwiredLints::lint_vec());
diff --git a/compiler/rustc_lint/src/module_inception.rs b/compiler/rustc_lint/src/module_inception.rs
new file mode 100644
index 0000000000000..27ba6f95ab5df
--- /dev/null
+++ b/compiler/rustc_lint/src/module_inception.rs
@@ -0,0 +1,92 @@
+//! Lint for detecting modules that have the same name as their parent module.
+
+use rustc_hir::{Body, Item, ItemKind};
+use rustc_session::{declare_lint, impl_lint_pass};
+use rustc_span::Symbol;
+
+use crate::{LateContext, LateLintPass, LintContext};
+
+declare_lint! {
+    /// The `module_inception` lint detects modules that have the same name as their parent module.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// mod foo {
+    ///     mod foo {
+    ///         pub fn bar() {}
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// A typical beginner mistake is to have `mod foo;` and again `mod foo { .. }`
+    /// in `foo.rs`. The expectation is that items inside the inner `mod foo { .. }`
+    /// are then available through `foo::x`, but they are only available through
+    /// `foo::foo::x`. If this is done on purpose, it would be better to choose a
+    /// more representative module name.
+    pub MODULE_INCEPTION,
+    Warn,
+    "modules that have the same name as their parent module"
+}
+
+struct ModInfo {
+    name: Symbol,
+    /// How many bodies are between this module and the current lint pass position.
+    ///
+    /// Only the most recently seen module is updated when entering/exiting a body.
+    in_body_count: u32,
+}
+
+pub(crate) struct ModuleInception {
+    /// The module path the lint pass is in.
+    modules: Vec<ModInfo>,
+}
+
+impl ModuleInception {
+    pub(crate) fn new() -> Self {
+        Self { modules: Vec::new() }
+    }
+}
+
+impl_lint_pass!(ModuleInception => [MODULE_INCEPTION]);
+
+impl<'tcx> LateLintPass<'tcx> for ModuleInception {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
+        if let ItemKind::Mod(ident, _) = item.kind {
+            // Check if this module has the same name as its parent module
+            if let [.., prev] = &*self.modules
+                && prev.name == ident.name
+                && prev.in_body_count == 0
+                && !item.span.from_expansion()
+            {
+                cx.span_lint(MODULE_INCEPTION, item.span, |lint| {
+                    lint.primary_message("module has the same name as its containing module");
+                });
+            }
+
+            self.modules.push(ModInfo { name: ident.name, in_body_count: 0 });
+        }
+    }
+
+    fn check_item_post(&mut self, _cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
+        if matches!(item.kind, ItemKind::Mod(..)) {
+            self.modules.pop();
+        }
+    }
+
+    fn check_body(&mut self, _: &LateContext<'tcx>, _: &Body<'tcx>) {
+        if let [.., last] = &mut *self.modules {
+            last.in_body_count += 1;
+        }
+    }
+
+    fn check_body_post(&mut self, _: &LateContext<'tcx>, _: &Body<'tcx>) {
+        if let [.., last] = &mut *self.modules {
+            last.in_body_count -= 1;
+        }
+    }
+}
diff --git a/library/core/src/async_iter/mod.rs b/library/core/src/async_iter/mod.rs
index a5b03b7dd4f14..bc9a8eaccf0fb 100644
--- a/library/core/src/async_iter/mod.rs
+++ b/library/core/src/async_iter/mod.rs
@@ -121,6 +121,7 @@
 //! warning: unused result that must be used: async iterators do nothing unless polled
 //! ```
 
+#[allow(module_inception)]
 mod async_iter;
 mod from_iter;
 
diff --git a/library/core/src/future/mod.rs b/library/core/src/future/mod.rs
index 2b16a568b4031..c7dd2d344c8e3 100644
--- a/library/core/src/future/mod.rs
+++ b/library/core/src/future/mod.rs
@@ -13,6 +13,7 @@ use crate::ptr::NonNull;
 use crate::task::Context;
 
 mod async_drop;
+#[allow(module_inception)]
 mod future;
 mod into_future;
 mod join;
diff --git a/library/std/src/sys/process/unix/mod.rs b/library/std/src/sys/process/unix/mod.rs
index cda1bf74f1cad..7b5d10864abba 100644
--- a/library/std/src/sys/process/unix/mod.rs
+++ b/library/std/src/sys/process/unix/mod.rs
@@ -16,6 +16,7 @@ cfg_select! {
         pub use unsupported::output;
     }
     _ => {
+        #[allow(module_inception)]
         mod unix;
         use unix as imp;
     }
diff --git a/library/test/src/lib.rs b/library/test/src/lib.rs
index d554807bbde70..111120cc24f30 100644
--- a/library/test/src/lib.rs
+++ b/library/test/src/lib.rs
@@ -40,6 +40,7 @@ pub use self::types::TestName::*;
 pub use self::types::*;
 
 // Module to be used by rustc to compile tests in libtest
+#[allow(module_inception)]
 pub mod test {
     pub use crate::bench::Bencher;
     pub use crate::cli::{TestOpts, parse_opts};
diff --git a/src/bootstrap/src/core/config/mod.rs b/src/bootstrap/src/core/config/mod.rs
index 007ed4aaba13f..b62038c25e0c6 100644
--- a/src/bootstrap/src/core/config/mod.rs
+++ b/src/bootstrap/src/core/config/mod.rs
@@ -19,7 +19,7 @@
 //! - Utility enums for specific configuration options.
 //! - Helper functions for managing configuration values.
 
-#[expect(clippy::module_inception)]
+#[allow(unknown_lints, module_inception)]
 mod config;
 pub mod flags;
 pub mod target_selection;
diff --git a/tests/ui/expr/weird-exprs.rs b/tests/ui/expr/weird-exprs.rs
index 7db92d4606713..cd1bdda739b19 100644
--- a/tests/ui/expr/weird-exprs.rs
+++ b/tests/ui/expr/weird-exprs.rs
@@ -10,6 +10,7 @@
 #![allow(uncommon_codepoints, confusable_idents)]
 #![allow(unused_imports)]
 #![allow(unreachable_patterns)]
+#![allow(module_inception)]
 
 #![recursion_limit = "256"]
 
diff --git a/tests/ui/imports/issue-62767.rs b/tests/ui/imports/issue-62767.rs
index eb5569e003da0..32a867e0f1479 100644
--- a/tests/ui/imports/issue-62767.rs
+++ b/tests/ui/imports/issue-62767.rs
@@ -1,4 +1,5 @@
 //@ check-pass
+#![allow(module_inception)]
 
 // Minimized case from #62767.
 mod m {
diff --git a/tests/ui/lint/module-inception-allow.rs b/tests/ui/lint/module-inception-allow.rs
new file mode 100644
index 0000000000000..6715891aaa42c
--- /dev/null
+++ b/tests/ui/lint/module-inception-allow.rs
@@ -0,0 +1,24 @@
+#![allow(module_inception)]
+
+pub mod foo {
+    pub mod foo {
+        pub fn bar() {}
+    }
+}
+
+pub mod baz {
+    // This is fine - different name
+    pub fn qux() {}
+}
+
+pub mod outer {
+    pub mod outer {
+        pub fn inner() {}
+    }
+
+    pub mod different {
+        pub fn func() {}
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/lint/non-local-defs/convoluted-locals-131474-with-mods.rs b/tests/ui/lint/non-local-defs/convoluted-locals-131474-with-mods.rs
index 72fd056d461ad..20ac92262dcdb 100644
--- a/tests/ui/lint/non-local-defs/convoluted-locals-131474-with-mods.rs
+++ b/tests/ui/lint/non-local-defs/convoluted-locals-131474-with-mods.rs
@@ -4,6 +4,7 @@
 // Similar to https://github.com/rust-lang/rust/issues/131474
 
 //@ check-pass
+#![allow(module_inception)]
 
 pub mod tmp {
     pub mod tmp {
diff --git a/tests/ui/lint/non-local-defs/module_as_local.rs b/tests/ui/lint/non-local-defs/module_as_local.rs
index bb215026c7d40..43cb0e5a48efd 100644
--- a/tests/ui/lint/non-local-defs/module_as_local.rs
+++ b/tests/ui/lint/non-local-defs/module_as_local.rs
@@ -17,6 +17,7 @@ fn simple_one() {
 
 fn simple_two() {
     mod posts {
+        #[allow(module_inception)]
         pub mod posts {
             #[allow(non_camel_case_types)]
             pub struct table {}
diff --git a/tests/ui/structs-enums/rec-align-u64.rs b/tests/ui/structs-enums/rec-align-u64.rs
index df219892d7374..6d0ab50a42fd1 100644
--- a/tests/ui/structs-enums/rec-align-u64.rs
+++ b/tests/ui/structs-enums/rec-align-u64.rs
@@ -1,6 +1,8 @@
 //@ run-pass
 #![allow(dead_code)]
 #![allow(unused_unsafe)]
+#![allow(module_inception)]
+
 
 // Issue #2303