feat: LSP autocompletion for use statement (#5704)

# Description

## Problem

Part of #1577

## Summary

Implements autocompletion for use statements, so typing anything after
`use`.


https://github.com/user-attachments/assets/a9ecd738-30c2-41fc-8ea0-3ea93d5d99ab

Note: the gray hints are probably coming from copilot, I should have
turned it off before recording 😅

## Additional Context

To begin implementing autocompletion I thought starting with `use` would
be the easiest thing, but also not having to look up the std (or your
project) module hierarchy could be useful.

To implement this I had to allow parsing `use foo::`, that is, allowing
trailing colons, because otherwise that wouldn't parse to a use
statement and we wouldn't have any information to do the autocompletion.

There are still some cases that don't work. For example if you write
`use ` and explicitly ask for autocompletion, you don't get anything.
The reason is that `use ` gives a parse error so no AST is produced. We
could tackle those in later PRs (I didn't want to continue making this
PR bigger).

This PR also introduces a simple way to test autocompletions, so next
autocompletion PRs should be much smaller.

Another thought: at first I was worried that caching `def_maps` in the
LSP state would increase the memory usage by a lot, but in retrospective
I think that's not a heavy data structure, or at least `NodeInterner`,
which was already cached, is probably much larger in memory footprint. I
tried this PR in a few projects and the memory usage was fine.

## Documentation

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_frontend/src/hir/def_map/module_data.rs

@@ -42,6 +42,10 @@ impl ModuleData {
         &self.scope
     }
 
+    pub fn definitions(&self) -> &ItemScope {
+        &self.definitions
+    }
+
     fn declare(
         &mut self,
         name: Ident,

compiler/noirc_frontend/src/parser/errors.rs

@@ -16,6 +16,8 @@ pub enum ParserErrorReason {
     ExpectedFieldName(Token),
     #[error("expected a pattern but found a type - {0}")]
     ExpectedPatternButFoundType(Token),
+    #[error("expected an identifier after ::")]
+    ExpectedIdentifierAfterColons,
     #[error("Expected a ; separating these two statements")]
     MissingSeparatingSemi,
     #[error("constrain keyword is deprecated")]

compiler/noirc_frontend/src/parser/parser/path.rs

@@ -19,7 +19,19 @@ pub fn path_no_turbofish() -> impl NoirParser<Path> {
 }
 
 fn path_inner<'a>(segment: impl NoirParser<PathSegment> + 'a) -> impl NoirParser<Path> + 'a {
-    let segments = segment.separated_by(just(Token::DoubleColon)).at_least(1);
+    let segments = segment
+        .separated_by(just(Token::DoubleColon))
+        .at_least(1)
+        .then(just(Token::DoubleColon).then_ignore(none_of(Token::LeftBrace).rewind()).or_not())
+        .validate(|(path_segments, trailing_colons), span, emit_error| {
+            if trailing_colons.is_some() {
+                emit_error(ParserError::with_reason(
+                    ParserErrorReason::ExpectedIdentifierAfterColons,
+                    span,
+                ));
+            }
+            path_segments
+        });
     let make_path = |kind| move |segments, span| Path { segments, kind, span };
 
     let prefix = |key| keyword(key).ignore_then(just(Token::DoubleColon));
@@ -69,7 +81,7 @@ mod test {
     use super::*;
     use crate::parser::{
         parse_type,
-        parser::test_helpers::{parse_all_failing, parse_with},
+        parser::test_helpers::{parse_all_failing, parse_recover, parse_with},
     };
 
     #[test]
@@ -111,4 +123,18 @@ mod test {
             vec!["crate", "crate::std::crate", "foo::bar::crate", "foo::dep"],
         );
     }
+
+    #[test]
+    fn parse_path_with_trailing_colons() {
+        let src = "foo::bar::";
+
+        let (path, errors) = parse_recover(path_no_turbofish(), src);
+        let path = path.unwrap();
+        assert_eq!(path.segments.len(), 2);
+        assert_eq!(path.segments[0].ident.0.contents, "foo");
+        assert_eq!(path.segments[1].ident.0.contents, "bar");
+
+        assert_eq!(errors.len(), 1);
+        assert_eq!(errors[0].message, "expected an identifier after ::");
+    }
 }

tooling/lsp/src/lib.rs

@@ -22,8 +22,8 @@ use fm::{codespan_files as files, FileManager};
 use fxhash::FxHashSet;
 use lsp_types::{
     request::{
-        DocumentSymbolRequest, HoverRequest, InlayHintRequest, PrepareRenameRequest, References,
-        Rename,
+        Completion, DocumentSymbolRequest, HoverRequest, InlayHintRequest, PrepareRenameRequest,
+        References, Rename,
     },
     CodeLens,
 };
@@ -36,7 +36,10 @@ use nargo_toml::{find_file_manifest, resolve_workspace_from_toml, PackageSelecti
 use noirc_driver::{file_manager_with_stdlib, prepare_crate, NOIR_ARTIFACT_VERSION_STRING};
 use noirc_frontend::{
     graph::{CrateId, CrateName},
-    hir::{def_map::parse_file, Context, FunctionNameMatch, ParsedFiles},
+    hir::{
+        def_map::{parse_file, CrateDefMap},
+        Context, FunctionNameMatch, ParsedFiles,
+    },
     node_interner::NodeInterner,
     parser::ParserError,
     ParsedModule,
@@ -48,11 +51,11 @@ use notifications::{
     on_did_open_text_document, on_did_save_text_document, on_exit, on_initialized,
 };
 use requests::{
-    on_code_lens_request, on_document_symbol_request, on_formatting, on_goto_declaration_request,
-    on_goto_definition_request, on_goto_type_definition_request, on_hover_request, on_initialize,
-    on_inlay_hint_request, on_prepare_rename_request, on_profile_run_request,
-    on_references_request, on_rename_request, on_shutdown, on_test_run_request, on_tests_request,
-    LspInitializationOptions,
+    on_code_lens_request, on_completion_request, on_document_symbol_request, on_formatting,
+    on_goto_declaration_request, on_goto_definition_request, on_goto_type_definition_request,
+    on_hover_request, on_initialize, on_inlay_hint_request, on_prepare_rename_request,
+    on_profile_run_request, on_references_request, on_rename_request, on_shutdown,
+    on_test_run_request, on_tests_request, LspInitializationOptions,
 };
 use serde_json::Value as JsonValue;
 use thiserror::Error;
@@ -62,6 +65,7 @@ mod notifications;
 mod requests;
 mod solver;
 mod types;
+mod utils;
 
 #[cfg(test)]
 mod test_utils;
@@ -86,6 +90,7 @@ pub struct LspState {
     cached_lenses: HashMap<String, Vec<CodeLens>>,
     cached_definitions: HashMap<String, NodeInterner>,
     cached_parsed_files: HashMap<PathBuf, (usize, (ParsedModule, Vec<ParserError>))>,
+    cached_def_maps: HashMap<String, BTreeMap<CrateId, CrateDefMap>>,
     options: LspInitializationOptions,
 }
 
@@ -103,6 +108,7 @@ impl LspState {
             cached_definitions: HashMap::new(),
             open_documents_count: 0,
             cached_parsed_files: HashMap::new(),
+            cached_def_maps: HashMap::new(),
             options: Default::default(),
         }
     }
@@ -136,6 +142,7 @@ impl NargoLspService {
             .request::<Rename, _>(on_rename_request)
             .request::<HoverRequest, _>(on_hover_request)
             .request::<InlayHintRequest, _>(on_inlay_hint_request)
+            .request::<Completion, _>(on_completion_request)
             .notification::<notification::Initialized>(on_initialized)
             .notification::<notification::DidChangeConfiguration>(on_did_change_configuration)
             .notification::<notification::DidOpenTextDocument>(on_did_open_text_document)

tooling/lsp/src/notifications/mod.rs

@@ -30,7 +30,7 @@ pub(super) fn on_did_change_configuration(
     ControlFlow::Continue(())
 }
 
-pub(super) fn on_did_open_text_document(
+pub(crate) fn on_did_open_text_document(
     state: &mut LspState,
     params: DidOpenTextDocumentParams,
 ) -> ControlFlow<Result<(), async_lsp::Error>> {
@@ -153,8 +153,8 @@ pub(crate) fn process_workspace_for_noir_document(
                 Some(&file_path),
             );
             state.cached_lenses.insert(document_uri.to_string(), collected_lenses);
-
-            state.cached_definitions.insert(package_root_dir, context.def_interner);
+            state.cached_definitions.insert(package_root_dir.clone(), context.def_interner);
+            state.cached_def_maps.insert(package_root_dir.clone(), context.def_maps);
 
             let fm = &context.file_manager;
             let files = fm.as_file_map();