3 files changed, 88 insertions, 8 deletions

diff --git a/crates/hir_ty/src/diagnostics/decl_check.rs b/crates/hir_ty/src/diagnostics/decl_check.rs
index d1c51849a..3a95f1b82 100644
--- a/crates/hir_ty/src/diagnostics/decl_check.rs
+++ b/crates/hir_ty/src/diagnostics/decl_check.rs
@@ -19,7 +19,7 @@ use hir_expand::{
 };
 use syntax::{
     ast::{self, NameOwner},
-    AstPtr,
+    AstNode, AstPtr,
 };
 
 use crate::{
@@ -259,6 +259,21 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
                 if let Some(expr) = source_ptr.value.as_ref().left() {
                     let root = source_ptr.file_syntax(db.upcast());
                     if let ast::Pat::IdentPat(ident_pat) = expr.to_node(&root) {
+                        let parent = match ident_pat.syntax().parent() {
+                            Some(parent) => parent,
+                            None => continue,
+                        };
+
+                        // We have to check that it's either `let var = ...` or `Variant(_) @  var` statement,
+                        // because e.g. match arms are patterns as well.
+                        // In other words, we check that it's a named variable binding.
+                        if !ast::LetStmt::cast(parent.clone()).is_some()
+                            && !ast::IdentPat::cast(parent).is_some()
+                        {
+                            // This pattern is not an actual variable declaration, e.g. `Some(val) => {..}` match arm.
+                            continue;
+                        }
+
                         let diagnostic = IncorrectCase {
                             file: source_ptr.file_id,
                             ident_type: "Variable".to_string(),
@@ -663,7 +678,7 @@ fn foo2(ok_param: &str, CAPS_PARAM: u8) {}
             r#"
 fn foo() {
     let SOME_VALUE = 10;
-     // ^^^^^^^^^^ Variable `SOME_VALUE` should have a snake_case name, e.g. `some_value`
+     // ^^^^^^^^^^ Variable `SOME_VALUE` should have snake_case name, e.g. `some_value`
     let AnotherValue = 20;
      // ^^^^^^^^^^^^ Variable `AnotherValue` should have snake_case name, e.g. `another_value`
 }
@@ -761,4 +776,37 @@ impl someStruct {
 "#,
         );
     }
+
+    #[test]
+    fn no_diagnostic_for_enum_varinats() {
+        check_diagnostics(
+            r#"
+enum Option { Some, None }
+
+fn main() {
+    match Option::None {
+        None => (),
+        Some => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn non_let_bind() {
+        check_diagnostics(
+            r#"
+enum Option { Some, None }
+
+fn main() {
+    match Option::None {
+        None @ SOME_VAR => (),
+            // ^^^^^^^^ Variable `SOME_VAR` should have snake_case name, e.g. `some_var`
+        Some => (),
+    }
+}
+"#,
+        );
+    }
 }
diff --git a/crates/hir_ty/src/diagnostics/decl_check/str_helpers.rs b/crates/hir_ty/src/diagnostics/decl_check/str_helpers.rs
index e3826909b..8f70c5e84 100644
--- a/crates/hir_ty/src/diagnostics/decl_check/str_helpers.rs
+++ b/crates/hir_ty/src/diagnostics/decl_check/str_helpers.rs
@@ -1,3 +1,6 @@
+//! Functions for string case manipulation, such as detecting the identifier case,
+//! and converting it into appropriate form.
+
 #[derive(Debug)]
 enum DetectedCase {
     LowerCamelCase,
@@ -44,6 +47,8 @@ fn detect_case(ident: &str) -> DetectedCase {
     }
 }
 
+/// Converts an identifier to an UpperCamelCase form.
+/// Returns `None` if the string is already is UpperCamelCase.
 pub fn to_camel_case(ident: &str) -> Option<String> {
     let detected_case = detect_case(ident);
 
@@ -87,9 +92,17 @@ pub fn to_camel_case(ident: &str) -> Option<String> {
         }
     }
 
-    Some(output)
+    if output == ident {
+        // While we didn't detect the correct case at the beginning, there
+        // may be special cases: e.g. `A` is both valid CamelCase and UPPER_SNAKE_CASE.
+        None
+    } else {
+        Some(output)
+    }
 }
 
+/// Converts an identifier to a lower_snake_case form.
+/// Returns `None` if the string is already is lower_snake_case.
 pub fn to_lower_snake_case(ident: &str) -> Option<String> {
     // First, assume that it's UPPER_SNAKE_CASE.
     match detect_case(ident) {
@@ -102,9 +115,18 @@ pub fn to_lower_snake_case(ident: &str) -> Option<String> {
 
     // Otherwise, assume that it's CamelCase.
     let lower_snake_case = stdx::to_lower_snake_case(ident);
-    Some(lower_snake_case)
+
+    if lower_snake_case == ident {
+        // While we didn't detect the correct case at the beginning, there
+        // may be special cases: e.g. `a` is both valid camelCase and snake_case.
+        None
+    } else {
+        Some(lower_snake_case)
+    }
 }
 
+/// Converts an identifier to an UPPER_SNAKE_CASE form.
+/// Returns `None` if the string is already is UPPER_SNAKE_CASE.
 pub fn to_upper_snake_case(ident: &str) -> Option<String> {
     match detect_case(ident) {
         DetectedCase::UpperSnakeCase => return None,
@@ -117,7 +139,14 @@ pub fn to_upper_snake_case(ident: &str) -> Option<String> {
     // Normalize the string from whatever form it's in currently, and then just make it uppercase.
     let upper_snake_case =
         stdx::to_lower_snake_case(ident).chars().map(|c| c.to_ascii_uppercase()).collect();
-    Some(upper_snake_case)
+
+    if upper_snake_case == ident {
+        // While we didn't detect the correct case at the beginning, there
+        // may be special cases: e.g. `A` is both valid CamelCase and UPPER_SNAKE_CASE.
+        None
+    } else {
+        Some(upper_snake_case)
+    }
 }
 
 #[cfg(test)]
@@ -139,6 +168,7 @@ mod tests {
         check(to_lower_snake_case, "Weird_Case", expect![["weird_case"]]);
         check(to_lower_snake_case, "CamelCase", expect![["camel_case"]]);
         check(to_lower_snake_case, "lowerCamelCase", expect![["lower_camel_case"]]);
+        check(to_lower_snake_case, "a", expect![[""]]);
     }
 
     #[test]
@@ -151,6 +181,7 @@ mod tests {
         check(to_camel_case, "UPPER_SNAKE_CASE", expect![["UpperSnakeCase"]]);
         check(to_camel_case, "Weird_Case", expect![["WeirdCase"]]);
         check(to_camel_case, "name", expect![["Name"]]);
+        check(to_camel_case, "A", expect![[""]]);
     }
 
     #[test]
@@ -160,5 +191,6 @@ mod tests {
         check(to_upper_snake_case, "Weird_Case", expect![["WEIRD_CASE"]]);
         check(to_upper_snake_case, "CamelCase", expect![["CAMEL_CASE"]]);
         check(to_upper_snake_case, "lowerCamelCase", expect![["LOWER_CAMEL_CASE"]]);
+        check(to_upper_snake_case, "A", expect![[""]]);
     }
 }
diff --git a/crates/hir_ty/src/diagnostics/unsafe_check.rs b/crates/hir_ty/src/diagnostics/unsafe_check.rs
index 61ffbf5d1..21a121aad 100644
--- a/crates/hir_ty/src/diagnostics/unsafe_check.rs
+++ b/crates/hir_ty/src/diagnostics/unsafe_check.rs
@@ -190,13 +190,13 @@ struct Ty {
     a: u8,
 }
 
-static mut static_mut: Ty = Ty { a: 0 };
+static mut STATIC_MUT: Ty = Ty { a: 0 };
 
 fn main() {
-    let x = static_mut.a;
+    let x = STATIC_MUT.a;
           //^^^^^^^^^^ This operation is unsafe and requires an unsafe function or block
     unsafe {
-        let x = static_mut.a;
+        let x = STATIC_MUT.a;
     }
 }
 "#,