Add list.index method

--
MOS_MIGRATED_REVID=107379557

2 files changed, 40 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/MethodLibrary.java b/src/main/java/com/google/devtools/build/lib/syntax/MethodLibrary.java
index 3cc778984b..dbbb46ff47 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/MethodLibrary.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/MethodLibrary.java
@@ -882,6 +882,33 @@ public class MethodLibrary {
         }
       };
 
+  @SkylarkSignature(
+    name = "index",
+    objectType = MutableList.class,
+    returnType = Integer.class,
+    doc =
+        "Returns the index in the list of the first item whose value is x. "
+            + "It is an error if there is no such item.",
+    mandatoryPositionals = {
+      @Param(name = "self", type = MutableList.class, doc = "This string, a separator."),
+      @Param(name = "x", type = Object.class, doc = "The object to search.")
+    },
+    useLocation = true
+  )
+  private static BuiltinFunction listIndex =
+      new BuiltinFunction("index") {
+        public Integer invoke(MutableList self, Object x, Location loc) throws EvalException {
+          int i = 0;
+          for (Object obj : self) {
+            if (obj.equals(x)) {
+              return i;
+            }
+            i++;
+          }
+          throw new EvalException(loc, Printer.format("Item %r not found in list", x));
+        }
+      };
+
   // dictionary access operator
   @SkylarkSignature(name = "$index", documented = false, objectType = Map.class,
       doc = "Looks up a value in a dictionary.",
diff --git a/src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java b/src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java
index c78fba035c..eee12f78df 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java
@@ -858,6 +858,19 @@ public class MethodLibraryTest extends EvaluationTestCase {
   }
 
   @Test
+  public void testListIndexMethod() throws Exception {
+    new BothModesTest()
+        .testStatement("['a', 'b', 'c'].index('a')", 0)
+        .testStatement("['a', 'b', 'c'].index('b')", 1)
+        .testStatement("['a', 'b', 'c'].index('c')", 2)
+        .testStatement("[2, 4, 6].index(4)", 1)
+        .testStatement("[2, 4, 6].index(4)", 1)
+        .testStatement("[0, 1, [1]].index([1])", 2)
+        .testIfErrorContains("Item \"a\" not found in list", "[1, 2].index('a')")
+        .testIfErrorContains("Item 0 not found in list", "[].index(0)");
+  }
+
+  @Test
   public void testListIndex() throws Exception {
     new BothModesTest()
         .testStatement("['a', 'b', 'c', 'd'][0]", "a")