fix: correct patch commands for recursive diffs

diff/defs.bzl

@@ -70,10 +70,20 @@ def diff(name, srcs, args = ["--unified"], patch = None, **kwargs):
             partial.call(srcs[i], name = target, out = target + ".in")
             srcs[i] = target
 
+    # Determine whether patchable inputs are all source directories.
+    # Bazel rules cannot detect source directories. This information is
+    # needed to produce the correct patch command.
+    source_directories = False
+    if len(srcs) == 2:  # TODO: support multiple directory inputs with --to-file
+        all_sources = set(native.glob([srcs[0]], exclude_directories = 0, allow_empty = True))
+        file_sources = set(native.glob([srcs[0]], exclude_directories = 1, allow_empty = True))
+        source_directories = len(all_sources.difference(file_sources)) > 0
+
     diff_rule(
         name = name,
         args = args,
         srcs = srcs,
         patch = patch or name + ".patch",
+        source_directories = source_directories,
         **kwargs
     )

diff/private/diff.bzl

@@ -35,11 +35,21 @@ def _determine_patch_type(args):
 
     return "normal"
 
-def _patch_cmd(type, source_file, patch_file):
+def _is_recursive(args):
+    for arg in args:
+        arg = arg.lstrip(" ")
+        if arg.startswith("-r") or arg.startswith("--recursive"):
+            return True
+    return False
+
+def _patch_cmd(type, source_file, patch_file, recursive, source_directories):
     if type == "normal":
         return "(cd \\$(bazel info workspace); patch -p0 {} < {})".format(source_file, patch_file)
     elif type == "context" or type == "unified":
-        return "(cd \\$(bazel info workspace); patch -p0 < {})".format(patch_file)
+        if recursive and source_directories:
+            return "(cd \\$(bazel info workspace); patch --directory {} -p{} < {})".format(source_file, source_file.count("/") + 1, patch_file)
+        else:
+            return "(cd \\$(bazel info workspace); patch -p0 < {})".format(patch_file)
     return None
 
 def _detect_multifile(args):
@@ -137,6 +147,7 @@ def _diff_rule_impl(ctx):
         fail("error: srcs attr of diff rule must contain exactly two targets unless --from-file or --to-file are specified")
 
     type = _determine_patch_type(ctx.attr.args)
+    recursive = _is_recursive(ctx.attr.args)
 
     command = _build_command(
         ctx.bin_dir.path,
@@ -182,7 +193,7 @@ def _diff_rule_impl(ctx):
         if patchable:
             # Show a command to patch the source file if it's a (bazel) source file.
             # NB: the error message we print here allows the user to be in any working directory.
-            patch_cmd = _patch_cmd(type, ctx.files.srcs[0].path, ctx.outputs.patch.path)
+            patch_cmd = _patch_cmd(type, ctx.files.srcs[0].path, ctx.outputs.patch.path, recursive, ctx.attr.source_directories)
             if patch_cmd != None:
                 patch_msg = """
     To accept the diff, run:
@@ -211,6 +222,14 @@ diff_rule = rule(
             """,
             default = [],
         ),
+        "source_directories": attr.bool(
+            doc = """\
+              Whether all of the patchable source inputs in `srcs` are directories. This is expected
+              to be passed in by a wrapper macro as File.is_directory does not detect source directory
+              inputs.
+            """,
+            default = False,
+        ),
         "srcs": attr.label_list(allow_files = True),
         "patch": attr.output(
             doc = """\