Fix multiple Salsa assignment-declarations

Previously, all assignment-declarations needed to be of the same kind:
either all `this.p = ...` assignments or `C.prototype.p = ...`
assignments.

Author: sandersn

src/compiler/checker.ts

@@ -3166,17 +3166,17 @@ namespace ts {
                 }
 
                 let type: Type = undefined;
-                // Handle module.exports = expr or this.p = expr
-                if (declaration.kind === SyntaxKind.BinaryExpression) {
-                    type = getUnionType(map(symbol.declarations, (decl: BinaryExpression) => checkExpressionCached(decl.right)));
-                }
-                else if (declaration.kind === SyntaxKind.PropertyAccessExpression) {
-                    // Declarations only exist for property access expressions for certain
-                    // special assignment kinds
-                    if (declaration.parent.kind === SyntaxKind.BinaryExpression) {
-                        // Handle exports.p = expr  or className.prototype.method = expr
-                        type = checkExpressionCached((<BinaryExpression>declaration.parent).right);
-                    }
+                // Handle certain special assignment kinds, which happen to union across multiple declarations:
+                // * module.exports = expr
+                // * exports.p = expr
+                // * this.p = expr
+                // * className.prototype.method = expr
+                if (declaration.kind === SyntaxKind.BinaryExpression ||
+                    declaration.kind === SyntaxKind.PropertyAccessExpression && declaration.parent.kind === SyntaxKind.BinaryExpression) {
+                    type = getUnionType(map(symbol.declarations,
+                                            decl => decl.kind === SyntaxKind.BinaryExpression ?
+                                                        checkExpressionCached((<BinaryExpression>decl).right) :
+                                                        checkExpressionCached((<BinaryExpression>decl.parent).right)));
                 }
 
                 if (type === undefined) {