4 files changed, 169 insertions, 5 deletions

diff --git a/crates/ide/src/diagnostics.rs b/crates/ide/src/diagnostics.rs
index f5d627b6e..b30cdb6ed 100644
--- a/crates/ide/src/diagnostics.rs
+++ b/crates/ide/src/diagnostics.rs
@@ -96,6 +96,9 @@ pub(crate) fn diagnostics(
         .on::<hir::diagnostics::NoSuchField, _>(|d| {
             res.borrow_mut().push(diagnostic_with_fix(d, &sema));
         })
+        .on::<hir::diagnostics::IncorrectCase, _>(|d| {
+            res.borrow_mut().push(warning_with_fix(d, &sema));
+        })
         // Only collect experimental diagnostics when they're enabled.
         .filter(|diag| !(diag.is_experimental() && config.disable_experimental))
         .filter(|diag| !config.disabled.contains(diag.code().as_str()));
@@ -130,6 +133,15 @@ fn diagnostic_with_fix<D: DiagnosticWithFix>(d: &D, sema: &Semantics<RootDatabas
     }
 }
 
+fn warning_with_fix<D: DiagnosticWithFix>(d: &D, sema: &Semantics<RootDatabase>) -> Diagnostic {
+    Diagnostic {
+        range: sema.diagnostics_display_range(d).range,
+        message: d.message(),
+        severity: Severity::WeakWarning,
+        fix: d.fix(&sema),
+    }
+}
+
 fn check_unnecessary_braces_in_use_statement(
     acc: &mut Vec<Diagnostic>,
     file_id: FileId,
@@ -245,8 +257,37 @@ mod tests {
 
         assert_eq_text!(&after, &actual);
         assert!(
-            fix.fix_trigger_range.start() <= file_position.offset
-                && fix.fix_trigger_range.end() >= file_position.offset,
+            fix.fix_trigger_range.contains_inclusive(file_position.offset),
+            "diagnostic fix range {:?} does not touch cursor position {:?}",
+            fix.fix_trigger_range,
+            file_position.offset
+        );
+    }
+
+    /// Similar to `check_fix`, but applies all the available fixes.
+    fn check_fixes(ra_fixture_before: &str, ra_fixture_after: &str) {
+        let after = trim_indent(ra_fixture_after);
+
+        let (analysis, file_position) = fixture::position(ra_fixture_before);
+        let diagnostic = analysis
+            .diagnostics(&DiagnosticsConfig::default(), file_position.file_id)
+            .unwrap()
+            .pop()
+            .unwrap();
+        let fix = diagnostic.fix.unwrap();
+        let target_file_contents = analysis.file_text(file_position.file_id).unwrap();
+        let actual = {
+            let mut actual = target_file_contents.to_string();
+            // Go from the last one to the first one, so that ranges won't be affected by previous edits.
+            for edit in fix.source_change.source_file_edits.iter().rev() {
+                edit.edit.apply(&mut actual);
+            }
+            actual
+        };
+
+        assert_eq_text!(&after, &actual);
+        assert!(
+            fix.fix_trigger_range.contains_inclusive(file_position.offset),
             "diagnostic fix range {:?} does not touch cursor position {:?}",
             fix.fix_trigger_range,
             file_position.offset
@@ -790,4 +831,100 @@ struct Foo {
         let diagnostics = analysis.diagnostics(&DiagnosticsConfig::default(), file_id).unwrap();
         assert!(!diagnostics.is_empty());
     }
+
+    #[test]
+    fn test_rename_incorrect_case() {
+        check_fixes(
+            r#"
+pub struct test_struct<|> { one: i32 }
+
+pub fn some_fn(val: test_struct) -> test_struct {
+    test_struct { one: val.one + 1 }
+}
+"#,
+            r#"
+pub struct TestStruct { one: i32 }
+
+pub fn some_fn(val: TestStruct) -> TestStruct {
+    TestStruct { one: val.one + 1 }
+}
+"#,
+        );
+
+        check_fixes(
+            r#"
+pub fn some_fn(NonSnakeCase<|>: u8) -> u8 {
+    NonSnakeCase
+}
+"#,
+            r#"
+pub fn some_fn(non_snake_case: u8) -> u8 {
+    non_snake_case
+}
+"#,
+        );
+
+        check_fixes(
+            r#"
+pub fn SomeFn<|>(val: u8) -> u8 {
+    if val != 0 { SomeFn(val - 1) } else { val }
+}
+"#,
+            r#"
+pub fn some_fn(val: u8) -> u8 {
+    if val != 0 { some_fn(val - 1) } else { val }
+}
+"#,
+        );
+
+        check_fixes(
+            r#"
+fn some_fn() {
+    let whatAWeird_Formatting<|> = 10;
+    another_func(whatAWeird_Formatting);
+}
+"#,
+            r#"
+fn some_fn() {
+    let what_a_weird_formatting = 10;
+    another_func(what_a_weird_formatting);
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_uppercase_const_no_diagnostics() {
+        check_no_diagnostics(
+            r#"
+fn foo() {
+    const ANOTHER_ITEM<|>: &str = "some_item";
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_rename_incorrect_case_struct_method() {
+        check_fixes(
+            r#"
+pub struct TestStruct;
+
+impl TestStruct {
+    pub fn SomeFn<|>() -> TestStruct {
+        TestStruct
+    }
+}
+"#,
+            r#"
+pub struct TestStruct;
+
+impl TestStruct {
+    pub fn some_fn() -> TestStruct {
+        TestStruct
+    }
+}
+"#,
+        );
+    }
 }
diff --git a/crates/ide/src/diagnostics/fixes.rs b/crates/ide/src/diagnostics/fixes.rs
index 68ae1c239..0c75e50b0 100644
--- a/crates/ide/src/diagnostics/fixes.rs
+++ b/crates/ide/src/diagnostics/fixes.rs
@@ -3,7 +3,10 @@
 use base_db::FileId;
 use hir::{
     db::AstDatabase,
-    diagnostics::{Diagnostic, MissingFields, MissingOkInTailExpr, NoSuchField, UnresolvedModule},
+    diagnostics::{
+        Diagnostic, IncorrectCase, MissingFields, MissingOkInTailExpr, NoSuchField,
+        UnresolvedModule,
+    },
     HasSource, HirDisplay, Semantics, VariantDef,
 };
 use ide_db::{
@@ -17,7 +20,7 @@ use syntax::{
 };
 use text_edit::TextEdit;
 
-use crate::diagnostics::Fix;
+use crate::{diagnostics::Fix, references::rename::rename_with_semantics, FilePosition};
 
 /// A [Diagnostic] that potentially has a fix available.
 ///
@@ -99,6 +102,23 @@ impl DiagnosticWithFix for MissingOkInTailExpr {
     }
 }
 
+impl DiagnosticWithFix for IncorrectCase {
+    fn fix(&self, sema: &Semantics<RootDatabase>) -> Option<Fix> {
+        let root = sema.db.parse_or_expand(self.file)?;
+        let name_node = self.ident.to_node(&root);
+
+        let file_id = self.file.original_file(sema.db);
+        let offset = name_node.syntax().text_range().start();
+        let file_position = FilePosition { file_id, offset };
+
+        let rename_changes =
+            rename_with_semantics(sema, file_position, &self.suggested_text).ok()?;
+
+        let label = format!("Rename to {}", self.suggested_text);
+        Some(Fix::new(&label, rename_changes.info, rename_changes.range))
+    }
+}
+
 fn missing_record_expr_field_fix(
     sema: &Semantics<RootDatabase>,
     usage_file_id: FileId,
diff --git a/crates/ide/src/references.rs b/crates/ide/src/references.rs
index f65a05ea3..88e2f2db3 100644
--- a/crates/ide/src/references.rs
+++ b/crates/ide/src/references.rs
@@ -9,7 +9,7 @@
 //! at the index that the match starts at and its tree parent is
 //! resolved to the search element definition, we get a reference.
 
-mod rename;
+pub(crate) mod rename;
 
 use hir::Semantics;
 use ide_db::{
diff --git a/crates/ide/src/references/rename.rs b/crates/ide/src/references/rename.rs
index f3b5cfc8c..f9a11e43d 100644
--- a/crates/ide/src/references/rename.rs
+++ b/crates/ide/src/references/rename.rs
@@ -42,7 +42,14 @@ pub(crate) fn rename(
     new_name: &str,
 ) -> Result<RangeInfo<SourceChange>, RenameError> {
     let sema = Semantics::new(db);
+    rename_with_semantics(&sema, position, new_name)
+}
 
+pub(crate) fn rename_with_semantics(
+    sema: &Semantics<RootDatabase>,
+    position: FilePosition,
+    new_name: &str,
+) -> Result<RangeInfo<SourceChange>, RenameError> {
     match lex_single_syntax_kind(new_name) {
         Some(res) => match res {
             (SyntaxKind::IDENT, _) => (),