Improved invalid/unsupported NDK revision warning message.

Suggestion from @angersson on GitHub: https://github.com/bazelbuild/bazel/issues/4068#issuecomment-347627252

GITHUB: https://github.com/bazelbuild/bazel/issues/4068
RELNOTES: Improved clarity of warning message for unsupported NDK revisions.
PiperOrigin-RevId: 184852316

2 files changed, 12 insertions, 8 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/android/AndroidNdkRepositoryFunction.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/android/AndroidNdkRepositoryFunction.java
index 1e4e9b4e82..0f39042e49 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/android/AndroidNdkRepositoryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/android/AndroidNdkRepositoryFunction.java
@@ -175,17 +175,21 @@ public class AndroidNdkRepositoryFunction extends AndroidRepositoryFunction {
       String warningMessage =
           String.format(
               "The revision of the Android NDK referenced by android_ndk_repository rule '%s' "
-                  + "could not be determined (the revision string found is '%s'). Defaulting to "
-                  + "revision %s.",
-              ruleName, ndkRelease.rawRelease, AndroidNdkCrosstools.LATEST_KNOWN_REVISION.getKey());
+                  + "could not be determined (the revision string found is '%s'). "
+                  + "Bazel will attempt to treat the NDK as if it was r%s. This may cause "
+                  + "compilation and linkage problems. Please download a supported NDK version.\n",
+              ruleName,
+              ndkRelease.rawRelease,
+              AndroidNdkCrosstools.LATEST_KNOWN_REVISION.getKey());
       env.getListener().handle(Event.warn(warningMessage));
       ndkMajorRevision = AndroidNdkCrosstools.LATEST_KNOWN_REVISION.getValue();
     } else if (!AndroidNdkCrosstools.isKnownNDKRevision(ndkRelease)) {
       String warningMessage =
           String.format(
               "The major revision of the Android NDK referenced by android_ndk_repository rule "
-                  + "'%s' is %s. The major revisions supported by Bazel are %s. Defaulting to "
-                  + "revision %s.",
+                  + "'%s' is %s. The major revisions supported by Bazel are %s. Bazel will attempt "
+                  + "to treat the NDK as if it was r%s. This may cause compilation and linkage "
+                  + "problems. Please download a supported NDK version.\n",
               ruleName,
               ndkRelease.majorRevision,
               AndroidNdkCrosstools.KNOWN_NDK_MAJOR_REVISIONS.keySet(),
diff --git a/src/test/java/com/google/devtools/build/lib/bazel/rules/android/AndroidNdkRepositoryTest.java b/src/test/java/com/google/devtools/build/lib/bazel/rules/android/AndroidNdkRepositoryTest.java
index 3518fbc216..c2bfad33eb 100644
--- a/src/test/java/com/google/devtools/build/lib/bazel/rules/android/AndroidNdkRepositoryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/bazel/rules/android/AndroidNdkRepositoryTest.java
@@ -102,7 +102,7 @@ public class AndroidNdkRepositoryTest extends BuildViewTestCase {
         eventCollector,
         "The revision of the Android NDK referenced by android_ndk_repository rule 'androidndk' "
             + "could not be determined (the revision string found is 'not a valid release string')."
-            + " Defaulting to revision 14.");
+            + " Bazel will attempt to treat the NDK as if it was r14.");
   }
 
   @Test
@@ -128,7 +128,7 @@ public class AndroidNdkRepositoryTest extends BuildViewTestCase {
         eventCollector,
         "The revision of the Android NDK referenced by android_ndk_repository rule 'androidndk' "
             + "could not be determined (the revision string found is 'invalid package revision'). "
-            + "Defaulting to revision 14.");
+            + "Bazel will attempt to treat the NDK as if it was r14.");
   }
 
   @Test
@@ -153,7 +153,7 @@ public class AndroidNdkRepositoryTest extends BuildViewTestCase {
         eventCollector,
         "The major revision of the Android NDK referenced by android_ndk_repository rule "
             + "'androidndk' is 15. The major revisions supported by Bazel are [10, 11, 12, 13, 14]."
-            + " Defaulting to revision 14.");
+            + " Bazel will attempt to treat the NDK as if it was r14.");
   }
 
   @Test