Improve error message for select objects ('+' operator for incompatible types)

--
MOS_MIGRATED_REVID=107131704

3 files changed, 28 insertions, 4 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/EvalUtils.java b/src/main/java/com/google/devtools/build/lib/syntax/EvalUtils.java
index 0967917af7..d284427219 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/EvalUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/EvalUtils.java
@@ -265,6 +265,9 @@ public final class EvalUtils {
     } else if (object instanceof SkylarkNestedSet) {
       SkylarkNestedSet set = (SkylarkNestedSet) object;
       return "set" + (full ? " of " + set.getContentType() + "s" : "");
+    } else if (object instanceof SelectorList) {
+      SelectorList list = (SelectorList) object;
+      return "select" + (full ? " of " + getDataTypeNameFromClass(list.getType()) : "");
     } else {
       return getDataTypeNameFromClass(object.getClass());
     }
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SelectorList.java b/src/main/java/com/google/devtools/build/lib/syntax/SelectorList.java
index 60033c05b5..4d76524fe8 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/SelectorList.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SelectorList.java
@@ -60,7 +60,7 @@ public final class SelectorList {
   /**
    * Returns the native type contained by this expression.
    */
-  private Class<?> getType() {
+  public Class<?> getType() {
     return type;
   }
 
@@ -83,11 +83,16 @@ public final class SelectorList {
     Class<?> type1 = addValue(value1, builder);
     Class<?> type2 = addValue(value2, builder);
     if (!canConcatenate(type1, type2)) {
-      throw new EvalException(location, "'+' operator applied to incompatible types");
+      throw new EvalException(
+          location,
+          String.format(
+              "'+' operator applied to incompatible types (%s, %s)",
+              EvalUtils.getDataTypeName(value1, true),
+              EvalUtils.getDataTypeName(value2, true)));
     }
     return new SelectorList(type1, builder.build());
   }
-  
+
   // TODO(bazel-team): match on the List interface, not the actual implementation. For now,
   // we verify this is the right class through test coverage.
   private static final Class<?> NATIVE_LIST_TYPE = ArrayList.class;
@@ -126,4 +131,4 @@ public final class SelectorList {
   public String toString() {
     return Joiner.on(" + ").join(elements);
   }
-}
\ No newline at end of file
+}
diff --git a/src/test/java/com/google/devtools/build/lib/syntax/EvaluationTest.java b/src/test/java/com/google/devtools/build/lib/syntax/EvaluationTest.java
index 5a578e8e27..be1cf6d0db 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/EvaluationTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/EvaluationTest.java
@@ -530,6 +530,22 @@ public class EvaluationTest extends EvaluationTestCase {
   }
 
   @Test
+  public void testAddSelectIncompatibleType() throws Exception {
+    newTest()
+        .testIfErrorContains(
+            "'+' operator applied to incompatible types (select of list, int)",
+            "select({'foo': ['FOO'], 'bar': ['BAR']}) + 1");
+  }
+
+  @Test
+  public void testAddSelectIncompatibleType2() throws Exception {
+    newTest()
+        .testIfErrorContains(
+            "'+' operator applied to incompatible types (select of list, select of int)",
+            "select({'foo': ['FOO']}) + select({'bar': 2})");
+  }
+
+  @Test
   public void testListComprehensionFailsOnNonSequence() throws Exception {
     newTest().testIfErrorContains("type 'int' is not iterable", "[x + 1 for x in 123]");
   }