Implement a string concatenation gss function: concat(...)

This allows to dynamically construct urls, e.g.

@def HOST static.example.com
.img {
  background-image: url(concat('//', HOST, '/image.png');
}
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=105082418

src/com/google/common/css/compiler/gssfunctions/GssFunctions.java

@@ -32,6 +32,7 @@
 import com.google.common.css.compiler.ast.CssHexColorNode;
 import com.google.common.css.compiler.ast.CssLiteralNode;
 import com.google.common.css.compiler.ast.CssNumericNode;
+import com.google.common.css.compiler.ast.CssStringNode;
 import com.google.common.css.compiler.ast.CssValueNode;
 import com.google.common.css.compiler.ast.ErrorManager;
 import com.google.common.css.compiler.ast.GssError;
@@ -84,6 +85,9 @@ public static Map<String, GssFunction> getFunctionMap() {
  // Logic functions.
  .put("selectFrom", new SelectFrom())
 
+ // String functions.
+ .put("concat", new Concat())
+
  .build();
  }
 
@@ -463,8 +467,8 @@ public Color addValuesToHsbComponents(Color baseColor,
  */
  public static class MakeMutedColor implements GssFunction {
 
- private float LOSS_OF_SATURATION_FOR_MUTED_TONE = 0.2f;
- private String ARGUMENT_COUNT_ERROR_MESSAGE = "makeMutedColor " +
+ private final float LOSS_OF_SATURATION_FOR_MUTED_TONE = 0.2f;
+ private final String ARGUMENT_COUNT_ERROR_MESSAGE = "makeMutedColor " +
  "expected arguments: backgroundColorStr, foregroundColorStr and an " +
  "optional loss of saturation value (0 <= loss <= 1).";
 
@@ -573,6 +577,44 @@ public String getCallResultString(List<String> args) throws
  }
  }
 
+ /**
+ * Implementation of the concat(…) GssFunction. It concatenates a variable number of strings.
+ * e.g. concat('a', 'b') yields 'ab'. Mainly useful for use with constants.
+ */
+ public static class Concat implements GssFunction {
+
+ @Override
+ public Integer getNumExpectedArguments() {
+ return null; // Variable list of arguments
+ }
+
+ @Override
+ public List<CssValueNode> getCallResultNodes(List<CssValueNode> args, ErrorManager errorManager)
+ throws GssFunctionException {
+ StringBuilder result = new StringBuilder();
+ for (CssValueNode arg : args) {
+ result.append(arg.getValue());
+ }
+ return ImmutableList.of((CssValueNode) new CssStringNode(
+ CssStringNode.Type.SINGLE_QUOTED_STRING, result.toString()));
+ }
+
+ @Override
+ public String getCallResultString(List<String> args) throws GssFunctionException {
+ StringBuilder result = new StringBuilder();
+ for (String arg : args) {
+ if (arg.length() > 1 && ((arg.startsWith("'") && arg.endsWith("'"))
+ || (arg.startsWith("\"") && arg.endsWith("\"")))) {
+ result.append(CssStringNode.unescape(arg.substring(1, arg.length() - 1)));
+ } else {
+ result.append(arg);
+ }
+ }
+ return new CssStringNode(CssStringNode.Type.SINGLE_QUOTED_STRING, result.toString())
+ .toString();
+ }
+ }
+
 
  /**
  * Abstract class implementing the shared logic for the arithmetic functions.

tests/com/google/common/css/compiler/gssfunctions/DefaultGssFunctionMapProviderTest.java

@@ -185,4 +185,14 @@ public void testScalars() throws GssParserException {
  + "); }",
  "A { width: 60px; }");
  }
+
+ public void testConcat() throws GssParserException {
+ test("A { background-image:url(concat('http://', www, '.google.com', \"/example.gif\")); }",
+ "A { background-image:url('http://www.google.com/example.gif'); }");
+ test("A { x:concat(a); }", "A { x:'a'; }");
+ test("A { x:concat(\"'\", \"\\\"\", 'bar','\"', '\\''); }",
+ "A { x:'\\'\"bar\"\\'' }");
+ test("A { x:concat('\\\\\\\\'); }",
+ "A { x:'\\\\\\\\'; }");
+ }
 }

tests/com/google/common/css/compiler/gssfunctions/GssFunctionsTest.java

@@ -216,4 +216,17 @@ private void testFunctionCallFail(GssFunction funct, ImmutableList<String> args)
  // Expected to fail.
  }
  }
+
+ public void testConcat() throws Exception {
+ GssFunctions.Concat funct = new GssFunctions.Concat();
+ assertEquals("'ab'", funct.getCallResultString(ImmutableList.of("a", "b")));
+ assertEquals("'a'", funct.getCallResultString(ImmutableList.of("a")));
+ assertEquals("'a'", funct.getCallResultString(ImmutableList.of("'a'")));
+ assertEquals("'a'", funct.getCallResultString(ImmutableList.of("\"a\"")));
+ assertEquals("'abc'", funct.getCallResultString(ImmutableList.of("a", "b", "c")));
+ assertEquals("''", funct.getCallResultString(ImmutableList.<String>of()));
+ assertEquals("'ab'", funct.getCallResultString(ImmutableList.of("'a'", "'b'")));
+ assertEquals("'\"'", funct.getCallResultString(ImmutableList.of("'\"'")));
+ assertEquals("'\\''", funct.getCallResultString(ImmutableList.of("'")));
+ }
 }