From f8612c3d387ce90c1303740d6d91e0eb1a6e1cd4 Mon Sep 17 00:00:00 2001
From: Lauri Kotilainen <lauri@offbeat.fi>
Date: Fri, 5 May 2017 14:29:05 +0300
Subject: [PATCH] - Support interpolation in property names - Fixes #527

---
 src/dotless.Core/Parser/Parsers.cs         | 11 +++++++++++
 src/dotless.Core/Parser/Tree/Rule.cs       | 17 ++++++++++++++++-
 src/dotless.Test/Specs/VariablesFixture.cs | 16 ++++++++++++++++
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/src/dotless.Core/Parser/Parsers.cs b/src/dotless.Core/Parser/Parsers.cs
index 9a2235a9..8c6be6de 100644
--- a/src/dotless.Core/Parser/Parsers.cs
+++ b/src/dotless.Core/Parser/Parsers.cs
@@ -1202,11 +1202,18 @@ public Rule Rule(Parser parser)
 
             Variable variable = null;
             string name = Property(parser);
+            bool interpolatedName = false;
 
             if (string.IsNullOrEmpty(name)) {
                 variable = Variable(parser);
                 if (variable != null) {
                     name = variable.Name;
+                } else {
+                    var interpolation = InterpolatedVariable(parser);
+                    if (interpolation != null) {
+                        interpolatedName = true;
+                        name = interpolation.Name;
+                    }
                 }
             }
 
@@ -1251,6 +1258,10 @@ public Rule Rule(Parser parser)
 
                     var rule = NodeProvider.Rule(name, value,
                         parser.Tokenizer.GetNodeLocation(memo.TokenizerLocation.Index));
+                    if (interpolatedName) {
+                        rule.InterpolatedName = true;
+                        rule.Variable = false;
+                    }
                     rule.PostNameComments = postNameComments;
                     PopComments();
                     return rule;
diff --git a/src/dotless.Core/Parser/Tree/Rule.cs b/src/dotless.Core/Parser/Tree/Rule.cs
index 3299a3e6..4c62e4f0 100644
--- a/src/dotless.Core/Parser/Tree/Rule.cs
+++ b/src/dotless.Core/Parser/Tree/Rule.cs
@@ -14,6 +14,7 @@ public class Rule : Node
         public NodeList PostNameComments { get; set; }
         public bool IsSemiColonRequired { get; set; }
         public bool Variadic { get; set; }
+        public bool InterpolatedName { get; set; }
 
         public Rule(string name, Node value) : this(name, value, false)
         { 
@@ -37,7 +38,7 @@ public override Node Evaluate(Env env)
                 throw new ParsingException("No value found for rule " + Name, Location);
             }
 
-            var rule = new Rule(Name, Value.Evaluate(env)).ReducedFrom<Rule>(this);
+            var rule = new Rule(EvaluateName(env), Value.Evaluate(env)).ReducedFrom<Rule>(this);
             rule.IsSemiColonRequired = this.IsSemiColonRequired;
             rule.PostNameComments = this.PostNameComments;
 
@@ -46,6 +47,20 @@ public override Node Evaluate(Env env)
             return rule;
         }
 
+        private string EvaluateName(Env env) {
+            if (!InterpolatedName) {
+                return Name;
+            }
+
+            var evaluatedVariable = env.FindVariable(Name).Evaluate(env) as Rule;
+            var evaluatedValue = evaluatedVariable?.Value as Keyword;
+            if (evaluatedValue == null) {
+                throw new ParsingException("Invalid variable value for property name", Location);
+            }
+
+            return evaluatedValue.ToCSS(env);
+        }
+
         protected override Node CloneCore() {
             return new Rule(Name, Value.Clone(), Variadic) {
                 IsSemiColonRequired = IsSemiColonRequired,
diff --git a/src/dotless.Test/Specs/VariablesFixture.cs b/src/dotless.Test/Specs/VariablesFixture.cs
index 75c446c4..d35ca461 100644
--- a/src/dotless.Test/Specs/VariablesFixture.cs
+++ b/src/dotless.Test/Specs/VariablesFixture.cs
@@ -541,5 +541,21 @@ public void IndirectRecursiveVariableDefinition()
 ";
             AssertLess(input, "");
         }
+
+        [Test]
+        public void VariableInterpolationInPropertyName() {
+            var input = @"
+.test {
+  @var: color;
+  @{var}: red;
+}
+";
+
+            var expected = @"
+.test {
+  color: red;
+}";
+            AssertLess(input, expected);
+        }
     }
 }
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