Treat special property access symbol differently when retriving documentation

src/services/services.ts

@@ -4913,6 +4913,28 @@ namespace ts {
 
             if (!documentation) {
                 documentation = symbol.getDocumentationComment();
+                if (documentation.length === 0 && symbol.flags & SymbolFlags.Property) {
+                    // For some special property access expressions like `experts.foo = foo` or `module.exports.foo = foo`
+                    // there documentation comments might be attached to the right hand side symbol of their declarations.
+                    // The pattern of such special property access is that the parent symbol is the symbol of the file.
+                    if (symbol.parent && forEach(symbol.parent.declarations, declaration => declaration.kind === SyntaxKind.SourceFile)) {
+                        for (const declaration of symbol.declarations) {
+                            if (!declaration.parent || declaration.parent.kind !== SyntaxKind.BinaryExpression) {
+                                continue;
+                            }
+
+                            const rhsSymbol = program.getTypeChecker().getSymbolAtLocation((<BinaryExpression>declaration.parent).right);
+                            if (!rhsSymbol) {
+                                continue;
+                            }
+
+                            documentation = rhsSymbol.getDocumentationComment();
+                            if (documentation.length > 0) {
+                                break;
+                            }
+                        }
+                    }
+                }
             }
 
             return { displayParts, documentation, symbolKind };

tests/cases/fourslash/server/completionEntryDetailAcrossFiles01.ts

@@ -0,0 +1,20 @@
+/// <reference path="../fourslash.ts"/>
+
+// @allowNonTsExtensions: true
+// @Filename: a.js
+//// /**
+////  * Modify the parameter
+////  * @param {string} p1
+////  */
+//// var foo = function (p1) { }
+//// exports.foo = foo;
+//// fo/*1*/
+
+// @Filename: b.ts
+//// import a = require("./a");
+//// a.fo/*2*/
+
+goTo.marker('1');
+verify.completionEntryDetailIs("foo", "var foo: (p1: string) => void", "Modify the parameter");
+goTo.marker('2');
+verify.completionEntryDetailIs("foo", "(property) a.foo: (p1: string) => void", "Modify the parameter");