[PATCH 1/3] merge: allow reading the merge commit message from a file

[Johannes Schindelin via GitGitGadget]

From: Johannes Schindelin <johannes.schinde...@gmx.de>

This is consistent with `git commit` which, like `git merge`, supports
passing the commit message via `-m <msg>` and, unlike `git merge` before
this patch, via `-F <file>`.

It is useful to allow this for scripted use, or for the upcoming patch
to allow (re-)creating octopus merges in `git rebase --rebase-merges`.

Signed-off-by: Johannes Schindelin <johannes.schinde...@gmx.de>
---
 Documentation/git-merge.txt | 10 +++++++++-
 builtin/merge.c             | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-merge.txt b/Documentation/git-merge.txt
index 6a5c00e2c..537dca7fa 100644
--- a/Documentation/git-merge.txt
+++ b/Documentation/git-merge.txt
@@ -12,7 +12,7 @@ SYNOPSIS
 'git merge' [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
        [-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
        [--[no-]allow-unrelated-histories]
-       [--[no-]rerere-autoupdate] [-m <msg>] [<commit>...]
+       [--[no-]rerere-autoupdate] [-m <msg>] [-F <file>] [<commit>...]
 'git merge' --abort
 'git merge' --continue
 
@@ -75,6 +75,14 @@ The 'git fmt-merge-msg' command can be
 used to give a good default for automated 'git merge'
 invocations. The automated message can include the branch description.
 
+-F <file>::
+--file=<file>::
+       Read the commit message to be used for the merge commit (in
+       case one is created).
++
+If `--log` is specified, a shortlog of the commits being merged
+will be appended to the specified message.
+
 --[no-]rerere-autoupdate::
        Allow the rerere mechanism to update the index with the
        result of auto-conflict resolution if possible.
diff --git a/builtin/merge.c b/builtin/merge.c
index 4a4c09496..b0e907751 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -111,6 +111,35 @@ static int option_parse_message(const struct option *opt,
        return 0;
 }
 
+static int option_read_message(struct parse_opt_ctx_t *ctx,
+                              const struct option *opt, int unset)
+{
+       struct strbuf *buf = opt->value;
+       const char *arg;
+
+       if (unset)
+               BUG("-F cannot be negated");
+
+       if (ctx->opt) {
+               arg = ctx->opt;
+               ctx->opt = NULL;
+       } else if (ctx->argc > 1) {
+               ctx->argc--;
+               arg = *++ctx->argv;
+       } else
+               return opterror(opt, "requires a value", 0);
+
+       if (buf->len)
+               strbuf_addch(buf, '\n');
+       if (ctx->prefix && !is_absolute_path(arg))
+               arg = prefix_filename(ctx->prefix, arg);
+       if (strbuf_read_file(buf, arg, 0) < 0)
+               return error(_("could not read file '%s'"), arg);
+       have_message = 1;
+
+       return 0;
+}
+
 static struct strategy *get_strategy(const char *name)
 {
        int i;
@@ -228,6 +257,9 @@ static struct option builtin_merge_options[] = {
        OPT_CALLBACK('m', "message", &merge_msg, N_("message"),
                N_("merge commit message (for a non-fast-forward merge)"),
                option_parse_message),
+       { OPTION_LOWLEVEL_CALLBACK, 'F', "file", &merge_msg, N_("path"),
+               N_("read message from file"), PARSE_OPT_NONEG,
+               (parse_opt_cb *) option_read_message },
        OPT__VERBOSITY(&verbosity),
        OPT_BOOL(0, "abort", &abort_current_merge,
                N_("abort the current in-progress merge")),
-- 
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