Add type checking to select() keys.

Aside from making error messaging clearer, this stops Bazel from
crashing on select({None: ...}) (a pretty anti-social error message).

--
PiperOrigin-RevId: 146173043
MOS_MIGRATED_REVID=146173043

1 files changed, 10 insertions, 2 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/BazelLibrary.java b/src/main/java/com/google/devtools/build/lib/syntax/BazelLibrary.java
index c55e607003..b943e4aaab 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/BazelLibrary.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/BazelLibrary.java
@@ -172,11 +172,19 @@ public class BazelLibrary {
         defaultValue = "''",
         doc = "Optional custom error to report if no condition matches."
       )
-    }
+    },
+    useLocation = true
   )
   private static final BuiltinFunction select =
       new BuiltinFunction("select") {
-        public Object invoke(SkylarkDict<?, ?> dict, String noMatchError) throws EvalException {
+        public Object invoke(SkylarkDict<?, ?> dict, String noMatchError, Location loc)
+            throws EvalException {
+          for (Object key : dict.keySet()) {
+            if (!(key instanceof String)) {
+              throw new EvalException(loc,
+                  String.format("Invalid key: %s. select keys must be label references", key));
+            }
+          }
           return SelectorList.of(new SelectorValue(dict, noMatchError));
         }
       };