fix: Auto completion should use fully qualified syntax in case of ambiguity #18895

[asukaminato0721]

fix #18895

Updated the completion renderer to detect when a trait method is being completed via a type path and rewrite the edit to the UFCS form (<Ty as Trait>::method) before emitting the completion item, including the new UfcsData/CallSnippetRewrite plumbing and trait-container detection in render_fn so both plain inserts and call-paren snippets respect the wider replacement range.

Extended add_call_parens to accept the optional rewrite data, build snippets using the qualified call head, and emit a TextEdit that spans the entire qualifier when necessary.

Added helper utilities to compute the qualifier text/range, render the trait path, and decide when UFCS rewriting is appropriate so the logic stays isolated and testable.

Added a regression test that exercises completing Dog:: when only a trait implementation exists to ensure the completion now expands to <Dog as Animal>::baby_name().

[Copilot]

Pull request overview

This PR fixes auto-completion for trait methods accessed via type paths (e.g., Dog::). When a trait method is completed through a type qualifier, the completion now automatically rewrites it to use Universal Function Call Syntax (UFCS) in the form <Type as Trait>::method() to resolve ambiguity.

Key changes:

• Added UFCS detection and rewriting logic for trait method completions
• Extended call parentheses insertion to support qualified syntax with customizable replacement ranges
• Added regression test ensuring Dog::baby_name completes to <Dog as Animal>::baby_name()

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
crates/ide-completion/src/tests/expression.rs	Added regression test for UFCS syntax in trait method completion
crates/ide-completion/src/render/function.rs	Implemented UFCS detection, rewriting logic, and helper utilities for qualified trait method completion

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[Veykril]

We shouldn't fully qualify calls unless its necessary as outlined in the issue. The implementation here just always qualifies it which isn't quite what we want.