expand: work around incorrect globbing error

v3, currently in the master.v3 branch, doesn't have this bug as the
globbing code that calls ReadDir was refactored. This older code
performs two ReadDir calls, and one of them is run even if the current
potential glob path is not a dir.

This can be a problem if one performs a glob like "*/foo" and the file
"bar" exists; we should skip it, instead of erroring because it's not a
directory.

Fix that in a simple way in v2, and add a regression test.

Fixes #347.

expand/expand.go

@@ -709,7 +709,14 @@ func (cfg *Config) globDir(base, dir string, rx *regexp.Regexp, matches []string
 	}
 	infos, err := cfg.ReadDir(filepath.Join(base, dir))
 	if err != nil {
-		return nil, err
+		// Ignore the error, as this might be a file instead of a
+		// directory. v3 refactored globbing to only use one ReadDir
+		// call per directory instead of two, so it knows to skip this
+		// kind of path at the ReadDir call of its parent.
+		// Instead of backporting that complex rewrite into v2, just
+		// work around the edge case here. We might ignore other kinds
+		// of errors, but at least we don't fail on a correct glob.
+		return matches, nil
 	}
 	for _, info := range infos {
 		name := info.Name()

interp/interp_test.go

@@ -2087,6 +2087,10 @@ set +o pipefail
 		"mkdir x-d1 x-d2; touch x-f; echo ././x-*/// | sed -e 's@\\\\@/@g'",
 		"././x-d1/ ././x-d2/\n",
 	},
+	{
+		"mkdir -p x-d1/a x-d2/b; touch x-f; echo x-*/* | sed -e 's@\\\\@/@g'",
+		"x-d1/a x-d2/b\n",
+	},
 	{
 		"mkdir x-d; touch x-f; test -d $PWD/x-*/",
 		"",