Merge #11412

11412: fix: Include `fn`/`type`/`const` keyword in trait impl completion item source ranges r=Veykril a=The0x539

Fixes #11301

If the user has typed, say, `fn de` while implementing `Default`, or `type Ta` when implementing `Deref`, then the resulting completion suggestion will replace the entire "line", which, on its own, is fine.
However, the use of `ctx.source_range()` in this code was meant that `source_range` field of the `CompletionItem` covers only the identifier and not the preceding keyword.

Over in `rust_analyzer::to_proto::completion_item`, this caused the LSP completion response to be broken up into a text edit that replaces `de` with `fn default() -> Self {` and then an entry in `additional_text_edits` to remove the extra `fn`.
I'm pretty sure that using the field like that is (slightly) out of [spec](https://microsoft.github.io/language-server-protocol/specifications/specification-3-17/#completionItem):
> Edits must not overlap [...] with the main edit
> Additional text edits should be used to change text **unrelated to the current cursor position**

VS Code supports `additionalTextEdits` in such a way that this doesn't seem like a problem, so has gone largely unnoticed.
The various LSP clients I've tried, however, do not, and as a result this bug has been haunting me for ages.

Co-authored-by: The0x539 <[email protected]>

Author: bors[bot]

crates/ide_completion/src/completions/trait_impl.rs

@@ -145,10 +145,10 @@ fn add_function_impl(
     } else {
         CompletionItemKind::SymbolKind(SymbolKind::Function)
     };
-    let mut item = CompletionItem::new(completion_kind, ctx.source_range(), label);
-    item.lookup_by(fn_name).set_documentation(func.docs(ctx.db));
 
     let range = replacement_range(ctx, fn_def_node);
+    let mut item = CompletionItem::new(completion_kind, range, label);
+    item.lookup_by(fn_name).set_documentation(func.docs(ctx.db));
 
     if let Some(source) = ctx.sema.source(func) {
         let assoc_item = ast::AssocItem::Fn(source.value);
@@ -209,7 +209,7 @@ fn add_type_alias_impl(
     let snippet = format!("type {} = ", alias_name);
 
     let range = replacement_range(ctx, type_def_node);
-    let mut item = CompletionItem::new(SymbolKind::TypeAlias, ctx.source_range(), &snippet);
+    let mut item = CompletionItem::new(SymbolKind::TypeAlias, range, &snippet);
     item.text_edit(TextEdit::replace(range, snippet))
         .lookup_by(alias_name)
         .set_documentation(type_alias.docs(ctx.db));
@@ -237,7 +237,7 @@ fn add_const_impl(
                 let snippet = make_const_compl_syntax(&transformed_const);
 
                 let range = replacement_range(ctx, const_def_node);
-                let mut item = CompletionItem::new(SymbolKind::Const, ctx.source_range(), &snippet);
+                let mut item = CompletionItem::new(SymbolKind::Const, range, &snippet);
                 item.text_edit(TextEdit::replace(range, snippet))
                     .lookup_by(const_name)
                     .set_documentation(const_.docs(ctx.db));