Throw on empty comprehensions

src/comprehension.lsc

@@ -46,6 +46,7 @@ isSimpleObject(objExpr) ->
 retailObject(info, path, id, transformPathName, returnPathName) ->
   transformPath = path.get(transformPathName)
   validateComprehensionBody(transformPath)
+  let foundOne = false
   transformTails(
     transformPath
     true
@@ -59,6 +60,7 @@ retailObject(info, path, id, transformPathName, returnPathName) ->
           throw tailPath.buildCodeFrameError("Object comprehensions must end" +
           " with a (key, value) pair.")
 
+        now foundOne = true
         [ keyExpr, valExpr ] = expr.expressions
 
         return t.assignmentExpression("=",
@@ -69,6 +71,8 @@ retailObject(info, path, id, transformPathName, returnPathName) ->
       if not expr~isa("ObjectExpression"):
         throw tailPath.buildCodeFrameError("Object comprehensions must end with an object expression.")
 
+      now foundOne = true
+
       if expr~isSimpleObject():
         // Simple object case: { [k]: v } --> obj[k] = v
         { properties: [prop] } = expr
@@ -87,16 +91,21 @@ retailObject(info, path, id, transformPathName, returnPathName) ->
         )~atNode(expr)
   )
 
+  if not foundOne:
+    throw path.buildCodeFrameError("Object comprehensions must end with an object expression.")
+
   path.get(returnPathName).node
 
 retailArray(info, path, id, transformPathName, returnPathName) ->
   transformPath = path.get(transformPathName)
   validateComprehensionBody(transformPath)
+  let foundOne = false
   transformTails(
     transformPath
     true
     false
     (expr) ->
+      now foundOne = true
       t.callExpression(
         t.memberExpression(id, t.identifier("push")~atNode(expr))~atNode(expr)
         [expr]
@@ -117,6 +126,9 @@ retailArray(info, path, id, transformPathName, returnPathName) ->
       // )~atNode(expr)
   )
 
+  if not foundOne:
+    throw path.buildCodeFrameError("Array comprehensions must end with an expression.")
+
   path.get(returnPathName).node
 
 transformLoop(info, path, ref, stmts) ->

test/fixtures/enhanced-comprehensions/object-assign/actual.js

@@ -0,0 +1,3 @@
+{...for elem e in arr:
+  { [e]: e, [e+1]: e+1 }
+}

test/fixtures/enhanced-comprehensions/object-assign/exec.js

@@ -0,0 +1,5 @@
+obj = {...for let i=0; i<2; i++:
+  { [`${i}.0`]: i, [`${i}.1`]: i+1 }
+}
+
+assert.deepEqual(obj, { "0.0": 0, "0.1": 1, "1.0": 1, "1.1": 2 })

test/fixtures/enhanced-comprehensions/object-assign/expected.js

@@ -0,0 +1,6 @@
+(() => {
+  const _obj = {};for (let _i = 0, _len = arr.length; _i < _len; _i++) {
+    const e = arr[_i];
+    Object.assign(_obj, { [e]: e, [e + 1]: e + 1 });
+  }return _obj;
+})();

test/fixtures/enhanced-comprehensions/object-basic/actual.js

@@ -1 +1,8 @@
+{ ...for elem x in arr: ({a: x}) }
+
 { ...for elem x in arr: ({[x]: f(x)}) }
+
+{
+  a: b
+  ...if c: ({d: e})
+}

test/fixtures/enhanced-comprehensions/object-basic/expected.js

@@ -1,5 +1,18 @@
 (() => {
   const _obj = {};for (let _i = 0, _len = arr.length; _i < _len; _i++) {
-    const x = arr[_i];_obj[x] = f(x);
+    const x = arr[_i];_obj.a = x;
   }return _obj;
+})();
+
+(() => {
+  const _obj2 = {};for (let _i2 = 0, _len2 = arr.length; _i2 < _len2; _i2++) {
+    const x = arr[_i2];_obj2[x] = f(x);
+  }return _obj2;
+})();
+
+(() => {
+  const _obj3 = {
+    a: b
+  };if (c) _obj3.d = e;
+  return _obj3;
 })();

test/fixtures/enhanced-comprehensions/object-malformed-labeled-stmt/actual.js

@@ -0,0 +1 @@
+{ ...if true: { k: v } }

test/fixtures/enhanced-comprehensions/object-malformed-labeled-stmt/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Object comprehensions must end with an object expression."
+}