Support completion for grammar imports (#1106)

packages/langium/src/grammar/langium-grammar-module.ts

@@ -26,6 +26,7 @@ import { LangiumGrammarValidationResourcesCollector } from './validation/validat
 import { LangiumGrammarTypesValidator, registerTypeValidationChecks } from './validation/types-validator';
 import { interruptAndCheck } from '../utils/promise-util';
 import { DocumentState } from '../workspace/documents';
+import { LangiumGrammarCompletionProvider } from './lsp/grammar-completion-provider';
 
 export type LangiumGrammarAddedServices = {
     validation: {
@@ -49,7 +50,8 @@ export const LangiumGrammarModule: Module<LangiumGrammarServices, PartialLangium
         SemanticTokenProvider: (services) => new LangiumGrammarSemanticTokenProvider(services),
         Formatter: () => new LangiumGrammarFormatter(),
         DefinitionProvider: (services) => new LangiumGrammarDefinitionProvider(services),
-        CallHierarchyProvider: (services) => new LangiumGrammarCallHierarchyProvider(services)
+        CallHierarchyProvider: (services) => new LangiumGrammarCallHierarchyProvider(services),
+        CompletionProvider: (services) => new LangiumGrammarCompletionProvider(services)
     },
     references: {
         ScopeComputation: (services) => new LangiumGrammarScopeComputation(services),

packages/langium/src/grammar/lsp/grammar-completion-provider.ts

@@ -0,0 +1,93 @@
+/******************************************************************************
+ * Copyright 2023 TypeFox GmbH
+ * This program and the accompanying materials are made available under the
+ * terms of the MIT License, which is available in the project root.
+ ******************************************************************************/
+
+import type { Range } from 'vscode-languageserver-types';
+import { CompletionItemKind } from 'vscode-languageserver-types';
+import type { NextFeature } from '../../lsp/completion/follow-element-computation';
+import type { CompletionAcceptor, CompletionContext } from '../../lsp/completion/completion-provider';
+import { DefaultCompletionProvider } from '../../lsp/completion/completion-provider';
+import type { LangiumServices } from '../../services';
+import type { MaybePromise } from '../../utils/promise-util';
+import { getContainerOfType } from '../../utils/ast-util';
+import { equalURI, relativeURI } from '../../utils/uri-util';
+import type { LangiumDocument, LangiumDocuments } from '../../workspace';
+import type { AbstractElement } from '../generated/ast';
+import { isAssignment } from '../generated/ast';
+import { Utils } from 'vscode-uri';
+
+export class LangiumGrammarCompletionProvider extends DefaultCompletionProvider {
+
+    private readonly documents: () => LangiumDocuments;
+
+    constructor(services: LangiumServices) {
+        super(services);
+        this.documents = () => services.shared.workspace.LangiumDocuments;
+    }
+
+    protected override completionFor(context: CompletionContext, next: NextFeature<AbstractElement>, acceptor: CompletionAcceptor): MaybePromise<void> {
+        const assignment = getContainerOfType(next.feature, isAssignment);
+        if (assignment?.feature === 'path') {
+            this.completeImportPath(context, acceptor);
+        } else {
+            return super.completionFor(context, next, acceptor);
+        }
+    }
+
+    private completeImportPath(context: CompletionContext, acceptor: CompletionAcceptor): void {
+        const text = context.textDocument.getText();
+        const existingText = text.substring(context.tokenOffset, context.offset);
+        let allPaths = this.getAllFiles(context.document);
+        let range: Range = {
+            start: context.position,
+            end: context.position
+        };
+        if (existingText.length > 0) {
+            const existingPath = existingText.substring(1);
+            allPaths = allPaths.filter(path => path.startsWith(existingPath));
+            // Completely replace the current token
+            const start = context.textDocument.positionAt(context.tokenOffset + 1);
+            const end = context.textDocument.positionAt(context.tokenEndOffset - 1);
+            range = {
+                start,
+                end
+            };
+        }
+        for (const path of allPaths) {
+            // Only insert quotes if there is no `path` token yet.
+            const delimiter = existingText.length > 0 ? '' : '"';
+            const completionValue = `${delimiter}${path}${delimiter}`;
+            acceptor(context, {
+                label: path,
+                textEdit: {
+                    newText: completionValue,
+                    range
+                },
+                kind: CompletionItemKind.File,
+                sortText: '0'
+            });
+        }
+    }
+
+    private getAllFiles(document: LangiumDocument): string[] {
+        const documents = this.documents().all;
+        const uri = document.uri.toString();
+        const dirname = Utils.dirname(document.uri).toString();
+        const paths: string[] = [];
+        for (const doc of documents) {
+            if (!equalURI(doc.uri, uri)) {
+                const docUri = doc.uri.toString();
+                const uriWithoutExt = docUri.substring(0, docUri.length - Utils.extname(doc.uri).length);
+                let relativePath = relativeURI(dirname, uriWithoutExt);
+                if (!relativePath.startsWith('.')) {
+                    relativePath = `./${relativePath}`;
+                }
+                paths.push(relativePath);
+            }
+        }
+        return paths;
+    }
+
+}