MacOS: precompose_argv_prefix()

The following sequence leads to a "BUG" assertion running under MacOS:

  DIR=git-test-restore-p
  Adiarnfd=$(printf 'A\314\210')
  DIRNAME=xx${Adiarnfd}yy
  mkdir $DIR &&
  cd $DIR &&
  git init &&
  mkdir $DIRNAME &&
  cd $DIRNAME &&
  echo "Initial" >file &&
  git add file &&
  echo "One more line" >>file &&
  echo y | git restore -p .

 Initialized empty Git repository in /tmp/git-test-restore-p/.git/
 BUG: pathspec.c:495: error initializing pathspec_item
 Cannot close git diff-index --cached --numstat
 [snip]

The command `git restore` is run from a directory inside a Git repo.
Git needs to split the $CWD into 2 parts:
The path to the repo and "the rest", if any.
"The rest" becomes a "prefix" later used inside the pathspec code.

As an example, "/path/to/repo/dir-inside-repå" would determine
"/path/to/repo" as the root of the repo, the place where the
configuration file .git/config is found.

The rest becomes the prefix ("dir-inside-repå"), from where the
pathspec machinery expands the ".", more about this later.
If there is a decomposed form, (making the decomposing visible like this),
"dir-inside-rep°a" doesn't match "dir-inside-repå".

Git commands need to:

 (a) read the configuration variable "core.precomposeunicode"
 (b) precocompose argv[]
 (c) precompose the prefix, if there was any

The first commit,
76759c7dff53 "git on Mac OS and precomposed unicode"
addressed (a) and (b).

The call to precompose_argv() was added into parse-options.c,
because that seemed to be a good place when the patch was written.

Commands that don't use parse-options need to do (a) and (b) themselfs.

The commands `diff-files`, `diff-index`, `diff-tree` and `diff`
learned (a) and (b) in
commit 90a78b83e0b8 "diff: run arguments through precompose_argv"

Branch names (or refs in general) using decomposed code points
resulting in decomposed file names had been fixed in
commit 8e712ef6fc97 "Honor core.precomposeUnicode in more places"

The bug report from above shows 2 things:
- more commands need to handle precomposed unicode
- (c) should be implemented for all commands using pathspecs

Solution:
precompose_argv() now handles the prefix (if needed), and is renamed into
precompose_argv_prefix().

Inside this function the config variable core.precomposeunicode is read
into the global variable precomposed_unicode, as before.
This reading is skipped if precomposed_unicode had been read before.

The original patch for preocomposed unicode, 76759c7dff53, placed
precompose_argv() into parse-options.c

Now add it into git.c::run_builtin() as well.  Existing precompose
calls in diff-files.c and others may become redundant, and if we
audit the callflows that reach these places to make sure that they
can never be reached without going through the new call added to
run_builtin(), we might be able to remove these existing ones.

But in this commit, we do not bother to do so and leave these
precompose callsites as they are.  Because precompose() is
idempotent and can be called on an already precomposed string
safely, this is safer than removing existing calls without fully
vetting the callflows.

There is certainly room for cleanups - this change intends to be a bug fix.
Cleanups needs more tests in e.g. t/t3910-mac-os-precompose.sh, and should
be done in future commits.

[1] git-bugreport-2021-01-06-1209.txt (git can't deal with special characters)
[2] https://lore.kernel.org/git/A102844A-9501-4A86-854D-E3B387D378AA@icloud.com/

Reported-by: Daniel Troger <random_n0body@icloud.com>
Helped-By: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

5 files changed, 5 insertions, 5 deletions

diff --git a/builtin/diff-files.c b/builtin/diff-files.c
index 1e352dd8f7..e3851dd1c0 100644
--- a/builtin/diff-files.c
+++ b/builtin/diff-files.c
@@ -35,7 +35,7 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix)
 	 */
 	rev.diffopt.ita_invisible_in_index = 1;
 
-	precompose_argv(argc, argv);
+	prefix = precompose_argv_prefix(argc, argv, prefix);
 
 	argc = setup_revisions(argc, argv, &rev, NULL);
 	while (1 < argc && argv[1][0] == '-') {
diff --git a/builtin/diff-index.c b/builtin/diff-index.c
index 7f5281c461..c33d7af478 100644
--- a/builtin/diff-index.c
+++ b/builtin/diff-index.c
@@ -25,7 +25,7 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
 	repo_init_revisions(the_repository, &rev, prefix);
 	rev.abbrev = 0;
-	precompose_argv(argc, argv);
+	prefix = precompose_argv_prefix(argc, argv, prefix);
 
 	argc = setup_revisions(argc, argv, &rev, NULL);
 	for (i = 1; i < argc; i++) {
diff --git a/builtin/diff-tree.c b/builtin/diff-tree.c
index 9fc95e959f..178d12f07f 100644
--- a/builtin/diff-tree.c
+++ b/builtin/diff-tree.c
@@ -126,7 +126,7 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 	memset(&s_r_opt, 0, sizeof(s_r_opt));
 	s_r_opt.tweak = diff_tree_tweak_rev;
 
-	precompose_argv(argc, argv);
+	prefix = precompose_argv_prefix(argc, argv, prefix);
 	argc = setup_revisions(argc, argv, opt, &s_r_opt);
 
 	memset(&w, 0, sizeof(w));
diff --git a/builtin/diff.c b/builtin/diff.c
index 780c33877f..3c87c95967 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -452,7 +452,7 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 
 	init_diff_ui_defaults();
 	git_config(git_diff_ui_config, NULL);
-	precompose_argv(argc, argv);
+	prefix = precompose_argv_prefix(argc, argv, prefix);
 
 	repo_init_revisions(the_repository, &rev, prefix);
 
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index c30896c897..7fbad8a206 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -1257,7 +1257,7 @@ static int compute_summary_module_list(struct object_id *head_oid,
 	git_config(git_diff_basic_config, NULL);
 	init_revisions(&rev, info->prefix);
 	rev.abbrev = 0;
-	precompose_argv(diff_args.nr, diff_args.v);
+	precompose_argv_prefix(diff_args.nr, diff_args.v, NULL);
 	setup_revisions(diff_args.nr, diff_args.v, &rev, NULL);
 	rev.diffopt.output_format = DIFF_FORMAT_NO_OUTPUT | DIFF_FORMAT_CALLBACK;
 	rev.diffopt.format_callback = submodule_summary_callback;