Re: [PATCH 2/5] rebase: start implementing it as a builtin

[Stefan Beller <sbeller@google.com>]

On Thu, Jun 28, 2018 at 12:48 AM Pratik Karki <predatoramigo@gmail.com> wrote:
>
> This commit imitates the strategy that was used to convert the
> difftool to a builtin, see be8a90e (difftool: add a skeleton for the
> upcoming builtin, 2017-01-17) for details: This commit renames the
> shell script `git-rebase.sh` to `git-legacy-rebase.sh` and hands off to
> it by default.

That is a good way to start, imitating Johannes approach on rewriting
the difftool. Thanks for pointing this out.

> The current version of the builtin rebase does not, however, make full
> use of the internals but instead chooses to spawn a couple of Git
> processes to find out if we run the builtin or legacy rebase as that
> keeps the directory that we are in correct. There remains a lot
> of room for improvement, left for a later date. The following commits
> will recreate the functionality of the shell script, in pure C.
>
> We intentionally avoid reading the config directly to avoid
> messing up the GIT_* environment variables when we need to fall back to
> exec()ing the shell script.

Thanks for calling this out!

The test of builtin rebase can be done by
> `git -c rebase.useBuiltin=true rebase ...`
>
> Signed-off-by: Pratik Karki <predatoramigo@gmail.com>
> ---
>  .gitignore                            |  1 +
>  Makefile                              |  3 +-
>  builtin.h                             |  1 +
>  builtin/rebase.c                      | 55 +++++++++++++++++++++++++++
>  git-rebase.sh => git-legacy-rebase.sh |  0
>  git.c                                 |  6 +++
>  6 files changed, 65 insertions(+), 1 deletion(-)
>  create mode 100644 builtin/rebase.c
>  rename git-rebase.sh => git-legacy-rebase.sh (100%)
>
> diff --git a/.gitignore b/.gitignore
> index 3284a1e9b..ec2395901 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -78,6 +78,7 @@
>  /git-init-db
>  /git-interpret-trailers
>  /git-instaweb
> +/git-legacy-rebase
>  /git-log
>  /git-ls-files
>  /git-ls-remote
> diff --git a/Makefile b/Makefile
> index 0cb6590f2..e88fe2e5f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -609,7 +609,7 @@ SCRIPT_SH += git-merge-one-file.sh
>  SCRIPT_SH += git-merge-resolve.sh
>  SCRIPT_SH += git-mergetool.sh
>  SCRIPT_SH += git-quiltimport.sh
> -SCRIPT_SH += git-rebase.sh
> +SCRIPT_SH += git-legacy-rebase.sh
>  SCRIPT_SH += git-remote-testgit.sh
>  SCRIPT_SH += git-request-pull.sh
>  SCRIPT_SH += git-stash.sh
> @@ -1059,6 +1059,7 @@ BUILTIN_OBJS += builtin/prune.o
>  BUILTIN_OBJS += builtin/pull.o
>  BUILTIN_OBJS += builtin/push.o
>  BUILTIN_OBJS += builtin/read-tree.o
> +BUILTIN_OBJS += builtin/rebase.o
>  BUILTIN_OBJS += builtin/rebase--helper.o
>  BUILTIN_OBJS += builtin/receive-pack.o
>  BUILTIN_OBJS += builtin/reflog.o
> diff --git a/builtin.h b/builtin.h
> index 0362f1ce2..44651a447 100644
> --- a/builtin.h
> +++ b/builtin.h
> @@ -202,6 +202,7 @@ extern int cmd_prune_packed(int argc, const char **argv, const char *prefix);
>  extern int cmd_pull(int argc, const char **argv, const char *prefix);
>  extern int cmd_push(int argc, const char **argv, const char *prefix);
>  extern int cmd_read_tree(int argc, const char **argv, const char *prefix);
> +extern int cmd_rebase(int argc, const char **argv, const char *prefix);
>  extern int cmd_rebase__helper(int argc, const char **argv, const char *prefix);
>  extern int cmd_receive_pack(int argc, const char **argv, const char *prefix);
>  extern int cmd_reflog(int argc, const char **argv, const char *prefix);
> diff --git a/builtin/rebase.c b/builtin/rebase.c
> new file mode 100644
> index 000000000..1152b7229
> --- /dev/null
> +++ b/builtin/rebase.c
> @@ -0,0 +1,55 @@
> +/*
> + * "git rebase" builtin command
> + *
> + * Copyright (c) 2018 Pratik Karki
> + */
> +
> +#include "builtin.h"
> +#include "run-command.h"
> +#include "exec-cmd.h"
> +#include "argv-array.h"
> +#include "dir.h"
> +
> +static int use_builtin_rebase(void)
> +{
> +       struct child_process cp = CHILD_PROCESS_INIT;
> +       struct strbuf out = STRBUF_INIT;
> +       int ret;
> +
> +       argv_array_pushl(&cp.args,
> +                        "config", "--bool", "rebase.usebuiltin", NULL);

--bool is documented as "Historical options for selecting
a type specifier. Prefer instead --type, (see: above)." in the
man page of git-config. But as this code will go away once
the conversion is done, this is not kept around for long.
So we should be fine using the --bool option.

> +       cp.git_cmd = 1;
> +       if (capture_command(&cp, &out, 6))
> +               return 0;
> +
> +       strbuf_trim(&out);
> +       ret = !strcmp("true", out.buf);

As --bool will make sure that the config command
prints "true" or "false", even when the user configured
0 or 1 instead, this is fine.

> +       if (argc != 2)
> +               die("Usage: %s <base>", argv[0]);
> +       prefix = setup_git_directory();
> +       trace_repo_setup(prefix);
> +       setup_work_tree();
> +
> +       die("TODO");

When reading the last sentence in the commit message
("This can be tested ...") I shortly wondered how we adapt the tests
but as this is really just the skeleton, there is no need to adapt any tests.

This patch looks fine to me except for the nit that Christian points out.

Thanks!
Stefan