Recognize the RHS of assignments as the JSDoc target expression

Fixes #6552

(cherry picked from commit 364b08854bc1face5c9b38301bb83c7346f1ccce)

src/compiler/parser.ts

@@ -4051,7 +4051,7 @@ namespace ts {
                 setDecoratorContext(/*val*/ true);
             }
 
-            return finishNode(node);
+            return addJSDocComment(finishNode(node));
         }
 
         function parseOptionalIdentifier() {
@@ -4335,13 +4335,13 @@ namespace ts {
                 const labeledStatement = <LabeledStatement>createNode(SyntaxKind.LabeledStatement, fullStart);
                 labeledStatement.label = <Identifier>expression;
                 labeledStatement.statement = parseStatement();
-                return finishNode(labeledStatement);
+                return addJSDocComment(finishNode(labeledStatement));
             }
             else {
                 const expressionStatement = <ExpressionStatement>createNode(SyntaxKind.ExpressionStatement, fullStart);
                 expressionStatement.expression = expression;
                 parseSemicolon();
-                return finishNode(expressionStatement);
+                return addJSDocComment(finishNode(expressionStatement));
             }
         }
 

src/compiler/utilities.ts

@@ -1207,7 +1207,19 @@ namespace ts {
                 node.parent.parent.parent.kind === SyntaxKind.VariableStatement;
 
             const variableStatementNode = isInitializerOfVariableDeclarationInStatement ? node.parent.parent.parent : undefined;
-            return variableStatementNode && variableStatementNode.jsDocComment;
+            if (variableStatementNode) {
+                return variableStatementNode.jsDocComment;
+            }
+
+            // Also recognize when the node is the RHS of an assignment expression
+            const isSourceOfAssignmentExpressionStatement =
+                node.parent && node.parent.parent &&
+                node.parent.kind === SyntaxKind.BinaryExpression &&
+                (node.parent as BinaryExpression).operatorToken.kind === SyntaxKind.EqualsToken &&
+                node.parent.parent.kind === SyntaxKind.ExpressionStatement;
+            if (isSourceOfAssignmentExpressionStatement) {
+                return node.parent.parent.jsDocComment;
+            }
         }
 
         return undefined;

tests/cases/fourslash/getJavaScriptCompletions18.ts

@@ -0,0 +1,21 @@
+/// <reference path="fourslash.ts" />
+
+// @allowNonTsExtensions: true
+// @Filename: file.js
+//// /**
+////   * @param {number} a
+////   * @param {string} b
+//// */
+//// exports.foo = function(a, b) {
+//// 	a/*a*/;
+//// 	b/*b*/
+//// };
+
+goTo.marker('a');
+edit.insert('.');
+verify.completionListContains('toFixed', undefined, undefined, 'method');
+
+
+goTo.marker('b');
+edit.insert('.');
+verify.completionListContains('substr', undefined, undefined, 'method');