[CS2] destructured nested defaults [fixes #4566] (#4574)

* destructured nested defaults [fixes #4566]

* don't parenthesize nested assigns

lib/coffeescript/nodes.js

@@ -1544,7 +1544,7 @@
       }
 
       compileNode(o) {
-        var answer, i, idt, indent, isCompact, j, join, k, key, l, lastNoncom, len1, len2, len3, node, prop, props, ref1, value;
+        var answer, i, idt, indent, isCompact, j, join, k, key, l, lastNoncom, len1, len2, len3, len4, node, p, prop, props, ref1, unwrappedVal, value;
         props = this.properties;
         if (this.generated) {
           for (j = 0, len1 = props.length; j < len1; j++) {
@@ -1556,17 +1556,32 @@
         }
         idt = o.indent += TAB;
         lastNoncom = this.lastNonComment(this.properties);
+        if (this.lhs) {
+          for (k = 0, len2 = props.length; k < len2; k++) {
+            prop = props[k];
+            if (!(prop instanceof Assign)) {
+              continue;
+            }
+            ({value} = prop);
+            unwrappedVal = value.unwrapAll();
+            if (unwrappedVal instanceof Arr || unwrappedVal instanceof Obj) {
+              unwrappedVal.lhs = true;
+            } else if (unwrappedVal instanceof Assign) {
+              unwrappedVal.nestedLhs = true;
+            }
+          }
+        }
         isCompact = true;
         ref1 = this.properties;
-        for (k = 0, len2 = ref1.length; k < len2; k++) {
-          prop = ref1[k];
+        for (l = 0, len3 = ref1.length; l < len3; l++) {
+          prop = ref1[l];
           if (prop instanceof Comment || (prop instanceof Assign && prop.context === 'object' && !this.csx)) {
             isCompact = false;
           }
         }
         answer = [];
         answer.push(this.makeCode(isCompact ? '' : '\n'));
-        for (i = l = 0, len3 = props.length; l < len3; i = ++l) {
+        for (i = p = 0, len4 = props.length; p < len4; i = ++p) {
           prop = props[i];
           join = i === props.length - 1 ? '' : isCompact && this.csx ? ' ' : isCompact ? ', ' : prop === lastNoncom || prop instanceof Comment || this.csx ? '\n' : ',\n';
           indent = isCompact || prop instanceof Comment ? '' : idt;
@@ -2486,7 +2501,7 @@
           return compiledName.concat(this.makeCode(this.csx ? '=' : ': '), val);
         }
         answer = compiledName.concat(this.makeCode(` ${this.context || '='} `), val);
-        if (o.level > LEVEL_LIST || (isValue && this.variable.base instanceof Obj && !this.param)) {
+        if (o.level > LEVEL_LIST || (isValue && this.variable.base instanceof Obj && !this.nestedLhs && !this.param)) {
           return this.wrapInParentheses(answer);
         } else {
           return answer;

src/nodes.coffee

@@ -1165,6 +1165,17 @@ exports.Obj = class Obj extends Base
     idt        = o.indent += TAB
     lastNoncom = @lastNonComment @properties
 
+    # If this object is the left-hand side of an assignment, all its children
+    # are too.
+    if @lhs
+      for prop in props when prop instanceof Assign
+        {value} = prop
+        unwrappedVal = value.unwrapAll()
+        if unwrappedVal instanceof Arr or unwrappedVal instanceof Obj
+          unwrappedVal.lhs = yes
+        else if unwrappedVal instanceof Assign
+          unwrappedVal.nestedLhs = yes
+
     isCompact = yes
     for prop in @properties
       if prop instanceof Comment or (prop instanceof Assign and prop.context is 'object' and not @csx)
@@ -1828,7 +1839,7 @@ exports.Assign = class Assign extends Base
     answer = compiledName.concat @makeCode(" #{ @context or '=' } "), val
     # Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment#Assignment_without_declaration,
     # if we’re destructuring without declaring, the destructuring assignment must be wrapped in parentheses.
-    if o.level > LEVEL_LIST or (isValue and @variable.base instanceof Obj and not @param)
+    if o.level > LEVEL_LIST or (isValue and @variable.base instanceof Obj and not @nestedLhs and not @param)
       @wrapInParentheses answer
     else
       answer

test/assignment.coffee

@@ -571,3 +571,13 @@ test "Assignment to variables similar to helper functions", ->
 
   indexOf = [1, 2, 3]
   ok 2 in indexOf
+
+test "#4566: destructuring with nested default values", ->
+  {a: {b = 1}} = a: {}
+  eq 1, b
+
+  {c: {d} = {}} = c: d: 3
+  eq 3, d
+
+  {e: {f = 5} = {}} = {}
+  eq 5, f

test/functions.coffee

@@ -362,3 +362,8 @@ test "Destructured parameter with default value, that itself has a default value
       y: 30
     radius: 30
   eq output, 'big-18-30-30'
+
+test "#4566: destructuring with nested default values", ->
+  f = ({a: {b = 1}}) ->
+    b
+  eq 2, f a: b: 2