On type errors for select()s, show which branch is responsible.

Reviewed at: https://github.com/bazelbuild/bazel/pull/5425

PiperOrigin-RevId: 201241451

1 files changed, 5 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/packages/BuildType.java b/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
index 7f8d0d8e70..96042edbd0 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
@@ -577,7 +577,11 @@ public final class BuildType {
           result.put(key, originalType.getDefaultValue());
           defaultValuesBuilder.add(key);
         } else {
-          result.put(key, originalType.convert(entry.getValue(), what, context));
+          String selectBranch = what == null
+              ? null
+              : String.format("each branch in select expression of %s (including '%s')",
+                  what.toString(), key.toString());
+          result.put(key, originalType.convert(entry.getValue(), selectBranch, context));
         }
       }
       this.map = Collections.unmodifiableMap(result);