feat: inlay hint provider (#683)

Closes #679

### Summary of Changes

Show inlay hints for
* the type of block lambda results, placeholders, yields,
* the corresponding parameter for positional arguments.

src/language/helpers/nodeProperties.ts

@@ -81,6 +81,10 @@ export const isNamedArgument = (node: SdsArgument): boolean => {
     return Boolean(node.parameter);
 };
 
+export const isPositionalArgument = (node: SdsArgument): boolean => {
+    return !node.parameter;
+};
+
 export const isNamedTypeArgument = (node: SdsTypeArgument): boolean => {
     return Boolean(node.typeParameter);
 };

src/language/lsp/safe-ds-inlay-hint-provider.ts

@@ -0,0 +1,46 @@
+import { AbstractInlayHintProvider, AstNode, InlayHintAcceptor } from 'langium';
+import { SafeDsTypeComputer } from '../typing/safe-ds-type-computer.js';
+import { SafeDsNodeMapper } from '../helpers/safe-ds-node-mapper.js';
+import { SafeDsServices } from '../safe-ds-module.js';
+import { isSdsArgument, isSdsBlockLambdaResult, isSdsPlaceholder, isSdsYield } from '../generated/ast.js';
+import { isPositionalArgument } from '../helpers/nodeProperties.js';
+import { InlayHintKind } from 'vscode-languageserver';
+
+export class SafeDsInlayHintProvider extends AbstractInlayHintProvider {
+    private readonly nodeMapper: SafeDsNodeMapper;
+    private readonly typeComputer: SafeDsTypeComputer;
+
+    constructor(services: SafeDsServices) {
+        super();
+
+        this.nodeMapper = services.helpers.NodeMapper;
+        this.typeComputer = services.types.TypeComputer;
+    }
+
+    override computeInlayHint(node: AstNode, acceptor: InlayHintAcceptor) {
+        const cstNode = node.$cstNode;
+        /* c8 ignore start */
+        if (!cstNode) {
+            return;
+        }
+        /* c8 ignore stop */
+
+        if (isSdsArgument(node) && isPositionalArgument(node)) {
+            const parameter = this.nodeMapper.argumentToParameter(node);
+            if (parameter) {
+                acceptor({
+                    position: cstNode.range.start,
+                    label: `${parameter.name} = `,
+                    kind: InlayHintKind.Parameter,
+                });
+            }
+        } else if (isSdsBlockLambdaResult(node) || isSdsPlaceholder(node) || isSdsYield(node)) {
+            const type = this.typeComputer.computeType(node);
+            acceptor({
+                position: cstNode.range.end,
+                label: `: ${type}`,
+                kind: InlayHintKind.Type,
+            });
+        }
+    }
+}

src/language/safe-ds-module.ts

@@ -30,6 +30,7 @@ import { SafeDsNodeKindProvider } from './lsp/safe-ds-node-kind-provider.js';
 import { SafeDsDocumentSymbolProvider } from './lsp/safe-ds-document-symbol-provider.js';
 import { SafeDsDocumentBuilder } from './workspace/safe-ds-document-builder.js';
 import { SafeDsEnums } from './builtins/safe-ds-enums.js';
+import { SafeDsInlayHintProvider } from './lsp/safe-ds-inlay-hint-provider.js';
 
 /**
  * Declaration of custom services - add your own service classes here.
@@ -83,6 +84,7 @@ export const SafeDsModule: Module<SafeDsServices, PartialLangiumServices & SafeD
     lsp: {
         DocumentSymbolProvider: (services) => new SafeDsDocumentSymbolProvider(services),
         Formatter: () => new SafeDsFormatter(),
+        InlayHintProvider: (services) => new SafeDsInlayHintProvider(services),
         SemanticTokenProvider: (services) => new SafeDsSemanticTokenProvider(services),
     },
     parser: {

tests/language/lsp/safe-ds-inlay-hint-provider.test.ts

@@ -0,0 +1,188 @@
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { clearDocuments, parseHelper } from 'langium/test';
+import { createSafeDsServices } from '../../../src/language/safe-ds-module.js';
+import { Position } from 'vscode-languageserver';
+import { NodeFileSystem } from 'langium/node';
+import { findTestChecks } from '../../helpers/testChecks.js';
+import { URI } from 'langium';
+
+const services = createSafeDsServices(NodeFileSystem).SafeDs;
+const inlayHintProvider = services.lsp.InlayHintProvider!;
+const workspaceManager = services.shared.workspace.WorkspaceManager;
+const parse = parseHelper(services);
+
+describe('SafeDsInlayHintProvider', async () => {
+    beforeEach(async () => {
+        // Load the builtin library
+        await workspaceManager.initializeWorkspace([]);
+    });
+
+    afterEach(async () => {
+        await clearDocuments(services);
+    });
+
+    const testCases: InlayHintProviderTest[] = [
+        {
+            testName: 'resolved positional argument',
+            code: `
+                fun f(p: Int)
+
+                pipeline myPipeline {
+                    // $TEST$ before "p = "
+                    f(»«1);
+                }
+            `,
+        },
+        {
+            testName: 'unresolved positional argument',
+            code: `
+                fun f()
+
+                pipeline myPipeline {
+                    f(1);
+                }
+            `,
+        },
+        {
+            testName: 'named argument',
+            code: `
+                fun f(p: Int)
+
+                pipeline myPipeline {
+                    f(p = 1);
+                }
+            `,
+        },
+        {
+            testName: 'block lambda result',
+            code: `
+                pipeline myPipeline {
+                    () {
+                        // $TEST$ after ": literal<1>"
+                        yield r»« = 1;
+                    };
+                }
+            `,
+        },
+        {
+            testName: 'placeholder',
+            code: `
+                pipeline myPipeline {
+                    // $TEST$ after ": literal<1>"
+                    val x»« = 1;
+                }
+            `,
+        },
+        {
+            testName: 'wildcard',
+            code: `
+                pipeline myPipeline {
+                    _ = 1;
+                }
+            `,
+        },
+        {
+            testName: 'yield',
+            code: `
+                segment s() -> r: Int {
+                    // $TEST$ after ": literal<1>"
+                    yield r»« = 1;
+                }
+            `,
+        },
+    ];
+
+    it.each(testCases)('should assign the correct inlay hints ($testName)', async ({ code }) => {
+        const actualInlayHints = await getActualInlayHints(code);
+        const expectedInlayHints = getExpectedInlayHints(code);
+
+        expect(actualInlayHints).toStrictEqual(expectedInlayHints);
+    });
+});
+
+const getActualInlayHints = async (code: string): Promise<SimpleInlayHint[] | undefined> => {
+    const document = await parse(code);
+    const inlayHints = await inlayHintProvider.getInlayHints(document, {
+        range: document.parseResult.value.$cstNode!.range,
+        textDocument: { uri: document.textDocument.uri },
+    });
+
+    return inlayHints?.map((hint) => {
+        if (typeof hint.label === 'string') {
+            return {
+                label: hint.label,
+                position: hint.position,
+            };
+        } else {
+            return {
+                label: hint.label.join(''),
+                position: hint.position,
+            };
+        }
+    });
+};
+
+const getExpectedInlayHints = (code: string): SimpleInlayHint[] => {
+    const testChecks = findTestChecks(code, URI.file('file:///test.sdstest'), { failIfFewerRangesThanComments: true });
+    if (testChecks.isErr) {
+        throw new Error(testChecks.error.message);
+    }
+
+    return testChecks.value.map((check) => {
+        const range = check.location!.range;
+
+        const afterMatch = /after "(?<label>[^"]*)"/gu.exec(check.comment);
+        if (afterMatch) {
+            return {
+                label: afterMatch.groups!.label,
+                position: {
+                    line: range.start.line,
+                    character: range.start.character - 1,
+                },
+            };
+        }
+
+        const beforeMatch = /before "(?<label>[^"]*)"/gu.exec(check.comment);
+        if (beforeMatch) {
+            return {
+                label: beforeMatch.groups!.label,
+                position: {
+                    line: range.end.line,
+                    character: range.end.character + 1,
+                },
+            };
+        }
+
+        throw new Error('Incorrect test comment format');
+    });
+};
+
+/**
+ * A description of a test case for the inlay hint provider.
+ */
+interface InlayHintProviderTest {
+    /**
+     * A short description of the test case.
+     */
+    testName: string;
+
+    /**
+     * The code to parse.
+     */
+    code: string;
+}
+
+/**
+ * A simple inlay hint with some information removed.
+ */
+interface SimpleInlayHint {
+    /**
+     * The text of the inlay hint.
+     */
+    label: string;
+
+    /**
+     * The position of the inlay hint.
+     */
+    position: Position;
+}