feat: Implemented semantic code completion

crates/wit-language-server/Cargo.toml

@@ -15,6 +15,7 @@ rust-version.workspace = true
 [dependencies]
 clap = { workspace = true }
 color-eyre = { workspace = true }
+either = "1.10.0"
 im = { workspace = true }
 salsa = { workspace = true }
 serde = { workspace = true }

crates/wit-language-server/src/ops/completion.rs

@@ -0,0 +1,57 @@
+use either::Either;
+use tower_lsp::lsp_types::{
+    CompletionItem, CompletionItemKind, CompletionParams, CompletionResponse,
+};
+use wit_compiler::{
+    ast::{self, AstNode},
+    queries::{SourceFile, Workspace},
+};
+
+pub fn complete(
+    db: &dyn wit_compiler::Db,
+    _ws: Workspace,
+    file: SourceFile,
+    params: CompletionParams,
+) -> Option<CompletionResponse> {
+    let point = crate::utils::position_to_ts(params.text_document_position.position);
+
+    let mut completions = Vec::new();
+
+    // First, add all known keywords
+    let keywords = wit_compiler::ast::KEYWORDS.iter().map(|kw| CompletionItem {
+        label: kw.to_string(),
+        kind: Some(CompletionItemKind::KEYWORD),
+        ..Default::default()
+    });
+    completions.extend(keywords);
+
+    // Now, we do the hard job of figuring out which identifiers are in scope.
+    // FIXME: This doesn't take imported items into account
+    let items = wit_compiler::queries::file_items(db, file);
+    if let Some(index) = items.enclosing_item(db, point) {
+        let types = match index {
+            Either::Left(index) => items.get_world(db, index).items(db),
+            Either::Right(index) => items.get_interface(db, index).items(db),
+        };
+
+        completions.extend(types.names().map(|label| CompletionItem {
+            label: label.to_string(),
+            ..Default::default()
+        }));
+    }
+
+    let ast = wit_compiler::queries::parse(db, file);
+    if let Some(ident) = ast
+        .tree(db)
+        .ancestors(point)
+        .find_map(ast::Identifier::cast)
+    {
+        let src = file.contents(db);
+        let ident = ident.value(&src);
+        // The user has started writing an identifier, so limit the completions
+        // to whatever might match what they've written.
+        completions.retain(|c| c.label.starts_with(ident));
+    }
+
+    Some(CompletionResponse::Array(completions))
+}

crates/wit-language-server/src/ops/mod.rs

@@ -1,4 +1,5 @@
+mod completion;
 mod diagnostics;
 mod fold;
 
-pub use self::{diagnostics::file_diagnostics, fold::folding_range};
+pub use self::{completion::complete, diagnostics::file_diagnostics, fold::folding_range};

crates/wit-language-server/src/server.rs

@@ -4,12 +4,7 @@ use tokio::sync::{Mutex, MutexGuard};
 use tower_lsp::{
     jsonrpc::Error,
     lsp_types::{
-        DiagnosticOptions, DiagnosticServerCapabilities, DidChangeTextDocumentParams,
-        DidCloseTextDocumentParams, DidOpenTextDocumentParams, DidSaveTextDocumentParams,
-        DocumentDiagnosticParams, DocumentDiagnosticReportResult, FoldingRange, FoldingRangeParams,
-        InitializeParams, InitializeResult, SelectionRange, SelectionRangeParams,
-        ServerCapabilities, ServerInfo, TextDocumentContentChangeEvent, TextDocumentItem,
-        TextDocumentSyncCapability, TextDocumentSyncKind, Url,
+        CompletionOptions, CompletionParams, CompletionResponse, DiagnosticOptions, DiagnosticServerCapabilities, DidChangeTextDocumentParams, DidCloseTextDocumentParams, DidOpenTextDocumentParams, DidSaveTextDocumentParams, DocumentDiagnosticParams, DocumentDiagnosticReportResult, FoldingRange, FoldingRangeParams, InitializeParams, InitializeResult, SelectionRange, SelectionRangeParams, ServerCapabilities, ServerInfo, TextDocumentContentChangeEvent, TextDocumentItem, TextDocumentSyncCapability, TextDocumentSyncKind, Url
     },
     Client, ClientSocket, LspService,
 };
@@ -108,6 +103,7 @@ impl tower_lsp::LanguageServer for LanguageServer {
                         ..Default::default()
                     },
                 )),
+                completion_provider: Some(CompletionOptions::default()),
                 ..Default::default()
             },
             server_info: Some(ServerInfo {
@@ -248,10 +244,13 @@ impl tower_lsp::LanguageServer for LanguageServer {
         Ok(Some(ranges))
     }
 
+    #[tracing::instrument(level = "debug", skip_all)]
     async fn diagnostic(
         &self,
         params: DocumentDiagnosticParams,
     ) -> Result<DocumentDiagnosticReportResult, Error> {
+        tracing::debug!(document.uri=%params.text_document.uri);
+
         let snap = self.snapshot().await;
         let db = snap.wit_db();
         let path = &params.text_document.uri;
@@ -263,6 +262,22 @@ impl tower_lsp::LanguageServer for LanguageServer {
 
         Ok(crate::ops::file_diagnostics(db, snap.ws, file))
     }
+
+    #[tracing::instrument(level = "debug", skip_all)]
+    async fn completion(
+        &self,
+        params: CompletionParams,
+    ) -> Result<Option<CompletionResponse>, Error> {
+        let path = &params.text_document_position.text_document.uri;
+        tracing::debug!(document.uri=%path);
+        let snap = self.snapshot().await;
+
+        let Some(file) = snap.ws.lookup(snap.wit_db(), path.as_str()) else {
+            return Ok(None);
+        };
+
+        Ok(crate::ops::complete(snap.wit_db(), snap.ws, file, params))
+    }
 }
 
 fn selection_range(first: tree_sitter::Range, rest: Vector<tree_sitter::Range>) -> SelectionRange {

crates/wit-language-server/src/utils.rs

@@ -29,3 +29,10 @@ pub fn location_to_lsp(
         range: ts_to_range(range),
     }
 }
+
+pub fn position_to_ts(position: tower_lsp::lsp_types::Position) -> tree_sitter::Point {
+    tree_sitter::Point {
+        row: position.line as usize,
+        column: position.character as usize,
+    }
+}