Auto merge of #15736 - rmehri01:15678_module_incorrect_case_diagnostics, r=HKalbasi

fix: add incorrect case diagnostics for module names

Adds diagnostics for checking both inline and file module names are snake case.

Closes #15678

crates/hir-ty/src/diagnostics/decl_check.rs

@@ -9,6 +9,7 @@
 //! - constants (e.g. `const FOO: u8 = 10;`)
 //! - static items (e.g. `static FOO: u8 = 10;`)
 //! - match arm bindings (e.g. `foo @ Some(_)`)
+//! - modules (e.g. `mod foo { ... }` or `mod foo;`)
 
 mod case_conv;
 
@@ -19,7 +20,7 @@ use hir_def::{
     hir::{Pat, PatId},
     src::HasSource,
     AdtId, AttrDefId, ConstId, DefWithBodyId, EnumId, EnumVariantId, FunctionId, ItemContainerId,
-    Lookup, ModuleDefId, StaticId, StructId,
+    Lookup, ModuleDefId, ModuleId, StaticId, StructId,
 };
 use hir_expand::{
     name::{AsName, Name},
@@ -83,6 +84,7 @@ pub enum IdentType {
     Structure,
     Variable,
     Variant,
+    Module,
 }
 
 impl fmt::Display for IdentType {
@@ -97,6 +99,7 @@ impl fmt::Display for IdentType {
             IdentType::Structure => "Structure",
             IdentType::Variable => "Variable",
             IdentType::Variant => "Variant",
+            IdentType::Module => "Module",
         };
 
         repr.fmt(f)
@@ -132,6 +135,7 @@ impl<'a> DeclValidator<'a> {
 
     pub(super) fn validate_item(&mut self, item: ModuleDefId) {
         match item {
+            ModuleDefId::ModuleId(module_id) => self.validate_module(module_id),
             ModuleDefId::FunctionId(func) => self.validate_func(func),
             ModuleDefId::AdtId(adt) => self.validate_adt(adt),
             ModuleDefId::ConstId(const_id) => self.validate_const(const_id),
@@ -230,6 +234,55 @@ impl<'a> DeclValidator<'a> {
             || parent()
     }
 
+    fn validate_module(&mut self, module_id: ModuleId) {
+        // Check whether non-snake case identifiers are allowed for this module.
+        if self.allowed(module_id.into(), allow::NON_SNAKE_CASE, false) {
+            return;
+        }
+
+        // Check the module name.
+        let Some(module_name) = module_id.name(self.db.upcast()) else { return };
+        let module_name_replacement =
+            module_name.as_str().and_then(to_lower_snake_case).map(|new_name| Replacement {
+                current_name: module_name,
+                suggested_text: new_name,
+                expected_case: CaseType::LowerSnakeCase,
+            });
+
+        if let Some(module_name_replacement) = module_name_replacement {
+            let module_data = &module_id.def_map(self.db.upcast())[module_id.local_id];
+            let module_src = module_data.declaration_source(self.db.upcast());
+
+            if let Some(module_src) = module_src {
+                let ast_ptr = match module_src.value.name() {
+                    Some(name) => name,
+                    None => {
+                        never!(
+                            "Replacement ({:?}) was generated for a module without a name: {:?}",
+                            module_name_replacement,
+                            module_src
+                        );
+                        return;
+                    }
+                };
+
+                let diagnostic = IncorrectCase {
+                    file: module_src.file_id,
+                    ident_type: IdentType::Module,
+                    ident: AstPtr::new(&ast_ptr),
+                    expected_case: module_name_replacement.expected_case,
+                    ident_text: module_name_replacement
+                        .current_name
+                        .display(self.db.upcast())
+                        .to_string(),
+                    suggested_text: module_name_replacement.suggested_text,
+                };
+
+                self.sink.push(diagnostic);
+            }
+        }
+    }
+
     fn validate_func(&mut self, func: FunctionId) {
         let data = self.db.function_data(func);
         if matches!(func.lookup(self.db.upcast()).container, ItemContainerId::ExternBlockId(_)) {