Fix for empty destructuring patterns

wcjohnson · Jun 20, 2017 · 5e36dd3 · 5e36dd3
1 parent 7f8327e
commit 5e36dd3
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Showing 4 changed files with 13 additions and 9 deletions.
diff --git a/src/destructure.lsc b/src/destructure.lsc
@@ -14,6 +14,11 @@ export matchesDestructuringPattern(ref, pattern) ->
     | "ArrayPattern": ref~matchesArrayPattern(pattern)
     | "ObjectPattern": ref~matchesObjectPattern(pattern)
 
+export isNonEmptyPattern(pattern) ->
+  match pattern.type:
+    | "ArrayPattern": pattern.elements?.length > 0
+    | "ObjectPattern": pattern.properties?.length > 0
+
 ////////// Array pattern matching
 Bracket(array, i, element) ->
   t.memberExpression(
@@ -23,7 +28,7 @@ Bracket(array, i, element) ->
   )~atNode(element)
 
 HasLength(array, min, max, patternNode) ->
-  args = if max:
+  args = if max~looseNotEq(null):
     [ array, t.numericLiteral(min)~atNode(patternNode), t.numericLiteral(max)~atNode(patternNode) ]
   elif min > 0:
     [ array, t.numericLiteral(min)~atNode(patternNode) ]

diff --git a/src/match.lsc b/src/match.lsc
@@ -2,7 +2,7 @@ import t from './types'
 import { toBlockStatement } from './blocks'
 import { isa } from './is'
 import { undeclaredRef } from './ref'
-import { matchesDestructuringPattern, accessors } from './destructure'
+import { matchesDestructuringPattern, accessors, isNonEmptyPattern } from './destructure'
 import { createAndExpression as And, createOrExpression as Or } from './logical'
 import { runtime } from './runtime'
 import { checkFalsePositiveReference } from './variables'
@@ -114,7 +114,7 @@ transformBoundConsequent({discriminantRef}, binding, consequent) ->
 
 transformMatchConsequent(mtch, casePath) ->
   { binding, consequent } = casePath.node
-  if binding:
+  if binding and binding~isNonEmptyPattern():
     mtch~transformBoundConsequent(binding, consequent)
   else:
     consequent~toBlockStatement()

diff --git a/test/fixtures/match/arr-pattern/exec.js b/test/fixtures/match/arr-pattern/exec.js
@@ -5,10 +5,10 @@ assert.equal(
       "empty"
 )
 assert.equal(
-  "empty",
-  match []:
-    | with []:
-      "empty"
+  "nonempty",
+  match [1]:
+    | with []: "empty"
+    | with [first]: "nonempty"
 )
 assert.equal(
   undefined,

diff --git a/test/fixtures/match/arr-pattern/expected.js b/test/fixtures/match/arr-pattern/expected.js
@@ -1,6 +1,5 @@
 const _hasLength = require('@oigroup/lightscript-runtime/hasLength');
-if (_hasLength(x)) {
-  const [] = x;
+if (_hasLength(x, 0, 0)) {
   "empty";
 } else if (_hasLength(x, 2, 2)) {
   const [a, b] = x;