Properly exit calc mode after use (#3493)

Author: matthew-dean

lib/less/contexts.js

@@ -74,7 +74,7 @@ contexts.Eval.prototype.enterCalc = function () {
 
 contexts.Eval.prototype.exitCalc = function () {
     this.calcStack.pop();
-    if (!this.calcStack) {
+    if (!this.calcStack.length) {
         this.inCalc = false;
     }
 };

test/css/calc.css

@@ -17,3 +17,12 @@
 .c {
   height: calc(100% - ((10px * 3) + (10px * 2)));
 }
+.correctly-exit-calc-mode h2 {
+  width: 10px;
+}
+.correctly-exit-calc-mode div {
+  width: calc(100px * 2);
+}
+.correctly-exit-calc-mode h1 {
+  color: white;
+}

test/less/calc.less

@@ -27,4 +27,20 @@
 .c {
   @v: 10px;
   height: calc(100% - ((@v * 3) + (@v * 2)));
-}
+}
+
+.correctly-exit-calc-mode {
+    @a: 10;
+    h2 { width: unit(@a, px); }
+
+    div { width: calc(100px * 2); }
+
+    .mk-map() {
+        text: white;
+        background: black;
+    }
+
+    @p: .mk-map();
+
+    h1 { color: @p[text]; }
+}

test/sourcemaps/custom-props.json

@@ -1 +1 @@
-{"version":3,"sources":["testweb/sourcemaps/custom-props.less"],"names":[],"mappings":"AAEA;EACC,uBAHO,UAGP;EACA,OAAO,eAAP;EACA,gCAAA","file":"sourcemaps/custom-props.css"}
+{"version":3,"sources":["testweb/sourcemaps/custom-props.less"],"names":[],"mappings":"AAEA;EACC,uBAHO,UAGP;EACA,OAAO,eAAP;EACA,sBALO,UAKP","file":"sourcemaps/custom-props.css"}