Auto merge of rust-lang#17571 - winstxnhdw:bool-to-enum-no-dupe, r=Veykril

feat: do not add new enum if it already exists

## Summary

This PR introduces a check for the existence of another enum within the current scope, and if it exist, we skip `add_enum_def`.

## Why?

Currently, when using the `bool_to_enum` assist more than once, it is possible to add multiple enum definitions. For example, the following snippet,

```rs
#[derive(PartialEq, Eq)]
enum Bool {
    True,
    False,
}

fn main() {
    let a = Bool::True;
    let b = true;
    println!("Hello, world!");
}
```

will be transformed into,

```rs
#[derive(PartialEq, Eq)]
enum Bool {
    True,
    False,
}

#[derive(PartialEq, Eq)]
enum Bool {
    True,
    False,
}

fn main() {
    let a = Bool::True;
    let b = Bool::True;
    println!("Hello, world!");
}
```

This can be annoying for users to clean up.

Author: bors

src/tools/rust-analyzer/crates/ide-assists/src/handlers/bool_to_enum.rs

@@ -96,7 +96,7 @@ struct BoolNodeData {
 
 /// Attempts to find an appropriate node to apply the action to.
 fn find_bool_node(ctx: &AssistContext<'_>) -> Option<BoolNodeData> {
-    let name: ast::Name = ctx.find_node_at_offset()?;
+    let name = ctx.find_node_at_offset::<ast::Name>()?;
 
     if let Some(ident_pat) = name.syntax().parent().and_then(ast::IdentPat::cast) {
         let def = ctx.sema.to_def(&ident_pat)?;
@@ -461,7 +461,20 @@ fn add_enum_def(
     usages: &UsageSearchResult,
     target_node: SyntaxNode,
     target_module: &hir::Module,
-) {
+) -> Option<()> {
+    let insert_before = node_to_insert_before(target_node);
+
+    if ctx
+        .sema
+        .scope(&insert_before)?
+        .module()
+        .scope(ctx.db(), Some(*target_module))
+        .iter()
+        .any(|(name, _)| name.as_str() == Some("Bool"))
+    {
+        return None;
+    }
+
     let make_enum_pub = usages
         .iter()
         .flat_map(|(_, refs)| refs)
@@ -472,14 +485,15 @@ fn add_enum_def(
         .any(|module| module.nearest_non_block_module(ctx.db()) != *target_module);
     let enum_def = make_bool_enum(make_enum_pub);
 
-    let insert_before = node_to_insert_before(target_node);
     let indent = IndentLevel::from_node(&insert_before);
     enum_def.reindent_to(indent);
 
     edit.insert(
         insert_before.text_range().start(),
         format!("{}\n\n{indent}", enum_def.syntax().text()),
     );
+
+    Some(())
 }
 
 /// Finds where to put the new enum definition.
@@ -553,6 +567,33 @@ fn function(foo: Bool, bar: bool) {
         )
     }
 
+    #[test]
+    fn no_duplicate_enums() {
+        check_assist(
+            bool_to_enum,
+            r#"
+#[derive(PartialEq, Eq)]
+enum Bool { True, False }
+
+fn function(foo: bool, $0bar: bool) {
+    if bar {
+        println!("bar");
+    }
+}
+"#,
+            r#"
+#[derive(PartialEq, Eq)]
+enum Bool { True, False }
+
+fn function(foo: bool, bar: Bool) {
+    if bar == Bool::True {
+        println!("bar");
+    }
+}
+"#,
+        )
+    }
+
     #[test]
     fn parameter_with_last_param_usage() {
         check_assist(