Update the glob documentation to reflect a semantic change made a very long time ago where glob(['**'], exclude_directories = 0) doesn't match the package's directory. Also add tests for this behavior.

Also update Skyframe globbing to have these semantics. Any discrepancy has always been problematic, but now that we have Skyframe-hybrid globbing it's a lot more dangerous and consequential.

Alternatives considered: do this the other way around (keep the stale documentation as-is and instead update legacy globbing). This would potentially require changing existing usages from stuff like 'data = glob(["**"], exclude_directories = 0)' to 'data = [x for x in glob(["**"], exclude_directories = 0) where x != '']'. I think this is too messy, so long as there is a valid use-case for globs matching directories in the first place.

--
MOS_MIGRATED_REVID=115511504

2 files changed, 11 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm b/src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm
index e6d89c0054..b1b94dc40b 100644
--- a/src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm
+++ b/src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm
@@ -454,6 +454,15 @@ There are several important limitations and caveats:
     If a rule and a source file with the same name both exist in the package, the glob will
     return the outputs of the rule instead of the source file.
   </li>
+
+  <li>
+    The "**" wildcard has one corner case: the pattern
+    <code>"**"</code> doesn't match the package's directory path. That is to
+    say, <code>glob(["**"], exclude_directories = 0)</code> matches all files
+    and directories transitively strictly under the current package's directory
+    (but of course not going into directories of subpackages - see the previous
+    note about that).
+  </li>
 </ol>
 
 <p>
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/GlobFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/GlobFunction.java
index e1c877f455..e233cdfdd5 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/GlobFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/GlobFunction.java
@@ -90,7 +90,8 @@ public final class GlobFunction implements SkyFunction {
     // "**" also matches an empty segment, so try the case where it is not present.
     if ("**".equals(patternHead)) {
       if (patternTail == null) {
-        if (!glob.excludeDirs()) {
+        // Recursive globs aren't supposed to match the package's directory.
+        if (!glob.excludeDirs() && !globSubdir.equals(PathFragment.EMPTY_FRAGMENT)) {
           matches.add(globSubdir);
         }
       } else {