feat(27601): Copy JSDoc from type when destructing arguments

src/services/symbolDisplay.ts

@@ -584,6 +584,19 @@ namespace ts.SymbolDisplay {
             }
         }
 
+        if (documentation.length === 0 && isIdentifier(location) && symbol.valueDeclaration && isBindingElement(symbol.valueDeclaration)) {
+            const declaration = symbol.valueDeclaration;
+            const parent = declaration.parent;
+            if (isIdentifier(declaration.name) && isObjectBindingPattern(parent)) {
+                const name = getTextOfIdentifierOrLiteral(declaration.name);
+                const objectType = typeChecker.getTypeAtLocation(parent);
+                documentation = firstDefined(objectType.isUnion() ? objectType.types : [objectType], t => {
+                    const prop = t.getProperty(name);
+                    return prop ? prop.getDocumentationComment(typeChecker) : undefined;
+                }) || emptyArray;
+            }
+        }
+
         if (tags.length === 0 && !hasMultipleSignatures) {
             tags = symbol.getContextualJsDocTags(enclosingDeclaration, typeChecker);
         }

tests/baselines/reference/quickInfoForObjectBindingElementName03.baseline

@@ -0,0 +1,57 @@
+[
+  {
+    "marker": {
+      "fileName": "/tests/cases/fourslash/quickInfoForObjectBindingElementName03.ts",
+      "position": 122,
+      "name": "1"
+    },
+    "quickInfo": {
+      "kind": "parameter",
+      "kindModifiers": "",
+      "textSpan": {
+        "start": 119,
+        "length": 3
+      },
+      "displayParts": [
+        {
+          "text": "(",
+          "kind": "punctuation"
+        },
+        {
+          "text": "parameter",
+          "kind": "text"
+        },
+        {
+          "text": ")",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "foo",
+          "kind": "parameterName"
+        },
+        {
+          "text": ":",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "string",
+          "kind": "keyword"
+        }
+      ],
+      "documentation": [
+        {
+          "text": "A description of foo",
+          "kind": "text"
+        }
+      ]
+    }
+  }
+]

tests/baselines/reference/quickInfoForObjectBindingElementName04.baseline

@@ -0,0 +1,148 @@
+[
+  {
+    "marker": {
+      "fileName": "/tests/cases/fourslash/quickInfoForObjectBindingElementName04.ts",
+      "position": 193,
+      "name": "1"
+    },
+    "quickInfo": {
+      "kind": "parameter",
+      "kindModifiers": "",
+      "textSpan": {
+        "start": 192,
+        "length": 1
+      },
+      "displayParts": [
+        {
+          "text": "(",
+          "kind": "punctuation"
+        },
+        {
+          "text": "parameter",
+          "kind": "text"
+        },
+        {
+          "text": ")",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "a",
+          "kind": "parameterName"
+        },
+        {
+          "text": ":",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "{",
+          "kind": "punctuation"
+        },
+        {
+          "text": "\n",
+          "kind": "lineBreak"
+        },
+        {
+          "text": "    ",
+          "kind": "space"
+        },
+        {
+          "text": "b",
+          "kind": "propertyName"
+        },
+        {
+          "text": ":",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "string",
+          "kind": "keyword"
+        },
+        {
+          "text": ";",
+          "kind": "punctuation"
+        },
+        {
+          "text": "\n",
+          "kind": "lineBreak"
+        },
+        {
+          "text": "}",
+          "kind": "punctuation"
+        }
+      ],
+      "documentation": [
+        {
+          "text": "A description of 'a'",
+          "kind": "text"
+        }
+      ]
+    }
+  },
+  {
+    "marker": {
+      "fileName": "/tests/cases/fourslash/quickInfoForObjectBindingElementName04.ts",
+      "position": 200,
+      "name": "2"
+    },
+    "quickInfo": {
+      "kind": "parameter",
+      "kindModifiers": "",
+      "textSpan": {
+        "start": 199,
+        "length": 1
+      },
+      "displayParts": [
+        {
+          "text": "(",
+          "kind": "punctuation"
+        },
+        {
+          "text": "parameter",
+          "kind": "text"
+        },
+        {
+          "text": ")",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "b",
+          "kind": "parameterName"
+        },
+        {
+          "text": ":",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "string",
+          "kind": "keyword"
+        }
+      ],
+      "documentation": [
+        {
+          "text": "A description of 'b'",
+          "kind": "text"
+        }
+      ]
+    }
+  }
+]

tests/baselines/reference/quickInfoForObjectBindingElementName05.baseline

@@ -0,0 +1,73 @@
+[
+  {
+    "marker": {
+      "fileName": "/tests/cases/fourslash/quickInfoForObjectBindingElementName05.ts",
+      "position": 137,
+      "name": ""
+    },
+    "quickInfo": {
+      "kind": "parameter",
+      "kindModifiers": "",
+      "textSpan": {
+        "start": 136,
+        "length": 1
+      },
+      "displayParts": [
+        {
+          "text": "(",
+          "kind": "punctuation"
+        },
+        {
+          "text": "parameter",
+          "kind": "text"
+        },
+        {
+          "text": ")",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "a",
+          "kind": "parameterName"
+        },
+        {
+          "text": ":",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "string",
+          "kind": "keyword"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "|",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "number",
+          "kind": "keyword"
+        }
+      ],
+      "documentation": [
+        {
+          "text": "A description of a",
+          "kind": "text"
+        }
+      ]
+    }
+  }
+]

tests/cases/fourslash/quickInfoForObjectBindingElementName03.ts

@@ -0,0 +1,14 @@
+/// <reference path="fourslash.ts" />
+
+////interface Options {
+////    /**
+////     * A description of foo
+////     */
+////    foo: string;
+////}
+////
+////function f({ foo }: Options) {
+////    foo/*1*/;
+////}
+
+verify.baselineQuickInfo();

tests/cases/fourslash/quickInfoForObjectBindingElementName04.ts

@@ -0,0 +1,20 @@
+/// <reference path="fourslash.ts" />
+
+////interface Options {
+////   /**
+////    * A description of 'a'
+////    */
+////    a: {
+////       /**
+////        * A description of 'b'
+////        */
+////       b: string;
+////   }
+////}
+////
+////function f({ a, a: { b } }: Options) {
+////    a/*1*/;
+////    b/*2*/;
+////}
+
+verify.baselineQuickInfo();

tests/cases/fourslash/quickInfoForObjectBindingElementName05.ts

@@ -0,0 +1,17 @@
+/// <reference path="fourslash.ts" />
+
+////interface A {
+////    /**
+////     * A description of a
+////     */
+////    a: number;
+////}
+////interface B {
+////    a: string;
+////}
+////
+////function f({ a }: A | B) {
+////    a/**/;
+////}
+
+verify.baselineQuickInfo();