lint modules that have the same name as their parent module

clippy_lints/src/lib.rs

@@ -96,6 +96,7 @@ pub mod methods;
 pub mod minmax;
 pub mod misc;
 pub mod misc_early;
+pub mod module_inception;
 pub mod mut_mut;
 pub mod mut_reference;
 pub mod mutex_atomic;
@@ -173,6 +174,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
     reg.register_early_lint_pass(box utils::internal_lints::Clippy);
     reg.register_late_lint_pass(box types::TypePass);
     reg.register_late_lint_pass(box booleans::NonminimalBool);
+    reg.register_early_lint_pass(box module_inception::Pass);
     reg.register_late_lint_pass(box misc::TopLevelRefPass);
     reg.register_late_lint_pass(box misc::CmpNan);
     reg.register_late_lint_pass(box eq_op::EqOp);
@@ -384,6 +386,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
         misc_early::MIXED_CASE_HEX_LITERALS,
         misc_early::REDUNDANT_CLOSURE_CALL,
         misc_early::UNNEEDED_FIELD_PATTERN,
+        module_inception::MODULE_INCEPTION,
         mut_reference::UNNECESSARY_MUT_PASSED,
         mutex_atomic::MUTEX_ATOMIC,
         needless_bool::BOOL_COMPARISON,

clippy_lints/src/module_inception.rs

@@ -0,0 +1,47 @@
+use rustc::lint::*;
+use syntax::ast::*;
+use utils::span_lint;
+
+/// **What it does:** Checks for modules that have the same name as their parent module
+///
+/// **Why is this bad?** A typical beginner mistake is to have `mod foo;` and again `mod foo { .. }` in `foo.rs`
+///
+/// **Known problems:** None.
+///
+/// **Example:**
+/// ```rust
+/// // lib.rs
+/// mod foo;
+/// // foo.rs
+/// mod foo {
+///     ...
+/// }
+/// ```
+declare_lint! {
+    pub MODULE_INCEPTION,
+    Warn,
+    "modules that have the same name as their parent module"
+}
+
+pub struct Pass;
+
+impl LintPass for Pass {
+    fn get_lints(&self) -> LintArray {
+        lint_array![MODULE_INCEPTION]
+    }
+}
+
+impl EarlyLintPass for Pass {
+    fn check_item(&mut self, cx: &EarlyContext, item: &Item) {
+        if let ItemKind::Mod(ref module) = item.node {
+            for sub_item in &module.items {
+                if let ItemKind::Mod(_) = sub_item.node {
+                    if item.ident == sub_item.ident {
+                        span_lint(cx, MODULE_INCEPTION, sub_item.span,
+                                  "module has the same name as its containing module");
+                    }
+                }
+            }
+        }
+    }
+}