Fix stack depth computations for empty sequences

Part of a fix for GH-53.
13 years ago · 211a1116e4
parent afdcb6fc4f
commit 211a1116e4
2 changed files with 17 additions and 8 deletions
--- a/src/passes.js
+++ b/src/passes.js
@ -124,14 +124,18 @@ PEG.compiler.passes = {
      sequence:
        function(node) {
          each(node.elements, compute);
-          node.resultStackDepth = Math.max.apply(
+          node.resultStackDepth = node.elements.length > 0
+            ? Math.max.apply(
                null,
                map(node.elements, function(e, i) { return i + e.resultStackDepth; })
-          );
-          node.posStackDepth = 1 + Math.max.apply(
+              )
+            : 0;
+          node.posStackDepth = node.elements.length > 0
+            ? 1 + Math.max.apply(
                null,
                map(node.elements, function(e) { return e.posStackDepth; })
-          );
+              )
+            : 1;
        },

      labeled:      computeFromExpression(0, 0),
--- a/test/passes-test.js
+++ b/test/passes-test.js
@ -167,6 +167,11 @@ test("computes stack depths", function() {
    },

    /* Sequence */
+    {
+      grammar:          'start = ',
+      resultStackDepth: 1,
+      posStackDepth:    1
+    },
    {
      grammar:          'start = "a" "b" "c"',
      resultStackDepth: 3,