feat: tooltips for inlay hints (#721)

### Summary of Changes

Show tooltips on inlay code hints:

* For the corresponding parameter, its documentation is displayed.
* For named types, the documentation of the corresponding declaration is
used.

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

@@ -1,18 +1,21 @@
-import { AbstractInlayHintProvider, AstNode, InlayHintAcceptor } from 'langium';
+import { AbstractInlayHintProvider, AstNode, DocumentationProvider, 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';
+import { InlayHintKind, MarkupContent } from 'vscode-languageserver';
+import { NamedType } from '../typing/model.js';
 
 export class SafeDsInlayHintProvider extends AbstractInlayHintProvider {
+    private readonly documentationProvider: DocumentationProvider;
     private readonly nodeMapper: SafeDsNodeMapper;
     private readonly typeComputer: SafeDsTypeComputer;
 
     constructor(services: SafeDsServices) {
         super();
 
+        this.documentationProvider = services.documentation.DocumentationProvider;
         this.nodeMapper = services.helpers.NodeMapper;
         this.typeComputer = services.types.TypeComputer;
     }
@@ -32,15 +35,33 @@ export class SafeDsInlayHintProvider extends AbstractInlayHintProvider {
                     position: cstNode.range.start,
                     label: `${parameter.name} = `,
                     kind: InlayHintKind.Parameter,
+                    tooltip: createTooltip(this.documentationProvider.getDocumentation(parameter)),
                 });
             }
         } else if (isSdsBlockLambdaResult(node) || isSdsPlaceholder(node) || isSdsYield(node)) {
             const type = this.typeComputer.computeType(node);
+            let tooltip: MarkupContent | undefined = undefined;
+            if (type instanceof NamedType) {
+                tooltip = createTooltip(this.documentationProvider.getDocumentation(type.declaration));
+            }
+
             acceptor({
                 position: cstNode.range.end,
                 label: `: ${type}`,
                 kind: InlayHintKind.Type,
+                tooltip,
             });
         }
     }
 }
+
+const createTooltip = (documentation: string | undefined): MarkupContent | undefined => {
+    if (!documentation) {
+        return undefined;
+    }
+
+    return {
+        kind: 'markdown',
+        value: documentation,
+    };
+};

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

@@ -1,7 +1,7 @@
 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 { createSafeDsServices } from '../../../src/language/index.js';
+import { InlayHint, Position } from 'vscode-languageserver';
 import { NodeFileSystem } from 'langium/node';
 import { findTestChecks } from '../../helpers/testChecks.js';
 import { URI } from 'langium';
@@ -91,16 +91,91 @@ describe('SafeDsInlayHintProvider', async () => {
             `,
         },
     ];
-
     it.each(testCases)('should assign the correct inlay hints ($testName)', async ({ code }) => {
-        const actualInlayHints = await getActualInlayHints(code);
-        const expectedInlayHints = getExpectedInlayHints(code);
+        const actualInlayHints = await getActualSimpleInlayHints(code);
+        const expectedInlayHints = getExpectedSimpleInlayHints(code);
 
         expect(actualInlayHints).toStrictEqual(expectedInlayHints);
     });
+
+    it('should set the documentation of parameters as tooltip', async () => {
+        const code = `
+            /**
+             * @param p Lorem ipsum.
+             */
+            fun f(p: Int)
+
+            pipeline myPipeline {
+                f(1);
+            }
+        `;
+        const actualInlayHints = await getActualInlayHints(code);
+        const firstInlayHint = actualInlayHints?.[0];
+
+        expect(firstInlayHint?.tooltip).toStrictEqual({ kind: 'markdown', value: 'Lorem ipsum.' });
+    });
+
+    it.each([
+        {
+            testName: 'class',
+            code: `
+                /**
+                 * Lorem ipsum.
+                 */
+                class C()
+
+                pipeline myPipeline {
+                    val a = C();
+                }
+            `,
+        },
+        {
+            testName: 'enum',
+            code: `
+                /**
+                 * Lorem ipsum.
+                 */
+                enum E
+
+                fun f() -> e: E
+
+                pipeline myPipeline {
+                    val a = f();
+                }
+            `,
+        },
+        {
+            testName: 'enum variant',
+            code: `
+                enum E {
+                    /**
+                     * Lorem ipsum.
+                     */
+                    V
+                }
+
+                pipeline myPipeline {
+                    val a = E.V;
+                }
+            `,
+        },
+    ])('should set the documentation of named types as tooltip', async ({ code }) => {
+        const actualInlayHints = await getActualInlayHints(code);
+        const firstInlayHint = actualInlayHints?.[0];
+
+        expect(firstInlayHint?.tooltip).toStrictEqual({ kind: 'markdown', value: 'Lorem ipsum.' });
+    });
 });
 
-const getActualInlayHints = async (code: string): Promise<SimpleInlayHint[] | undefined> => {
+const getActualInlayHints = async (code: string): Promise<InlayHint[] | undefined> => {
+    const document = await parse(code);
+    return inlayHintProvider.getInlayHints(document, {
+        range: document.parseResult.value.$cstNode!.range,
+        textDocument: { uri: document.textDocument.uri },
+    });
+};
+
+const getActualSimpleInlayHints = async (code: string): Promise<SimpleInlayHint[] | undefined> => {
     const document = await parse(code);
     const inlayHints = await inlayHintProvider.getInlayHints(document, {
         range: document.parseResult.value.$cstNode!.range,
@@ -122,7 +197,7 @@ const getActualInlayHints = async (code: string): Promise<SimpleInlayHint[] | un
     });
 };
 
-const getExpectedInlayHints = (code: string): SimpleInlayHint[] => {
+const getExpectedSimpleInlayHints = (code: string): SimpleInlayHint[] => {
     const testChecks = findTestChecks(code, URI.file('file:///test.sdstest'), { failIfFewerRangesThanComments: true });
     if (testChecks.isErr) {
         throw new Error(testChecks.error.message);