[PATCH v3 01/11] Start to implement a built-in version of `git add --interactive`

From: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Date: Jul 16, 2019, 14:58 UTC
Message-ID: <0a5ec9345d2f9cc6cd348231219d4af428a28e94.1563289115.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.170.v3.git.gitgitgadget@gmail.com>

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

This is hardly the first conversion of a Git command that is implemented as a script to a built-in. So far, the most successful strategy for such conversions has been to add a built-in helper and call that for more and more functionality from the script, as more and more parts are converted.

With the interactive add, we choose a different strategy. The sole reason for this is that on Windows (where such a conversion has the most benefits in terms of speed and robustness) we face the very specific problem that a `system()` call in Perl seems to close `stdin` in the parent process when the spawned process consumes even one character from `stdin`. And that just does not work for us here, as it would stop the main loop as soon as any interactive command was performed by the helper. Which is almost all of the commands in `git add -i`.

It is almost as if Perl told us once again that it does not want us to use it on Windows.

Instead, we follow the opposite route where we start with a bare-bones version of the built-in interactive add, guarded by the new `add.interactive.useBuiltin` config variable, and then add more and more functionality to it, until it is feature complete.

At this point, the built-in version of `git add -i` only states that it cannot do anything yet ;-)

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 Documentation/config/add.txt |  5 +++++
 Makefile                     |  1 +
 add-interactive.c            |  7 +++++++
 add-interactive.h            |  8 ++++++++
 builtin/add.c                | 10 ++++++++++
 t/README                     |  4 ++++
 6 files changed, 35 insertions(+)
 create mode 100644 add-interactive.c
 create mode 100644 add-interactive.h

diff --git a/Documentation/config/add.txt b/Documentation/config/add.txt
index 4d753f006e..c9f748f81c 100644
--- a/Documentation/config/add.txt
+++ b/Documentation/config/add.txt
@@ -5,3 +5,8 @@ add.ignore-errors (deprecated)::
 	option of linkgit:git-add[1].  `add.ignore-errors` is deprecated,
 	as it does not follow the usual naming convention for configuration
 	variables.
+
+add.interactive.useBuiltin::
+	[EXPERIMENTAL] Set to `true` to use the experimental built-in
+	implementation of the interactive version of linkgit:git-add[1]
+	instead of the Perl script version. Is `false` by default.
diff --git a/Makefile b/Makefile
index 98a0588416..0a47200f47 100644
--- a/Makefile
+++ b/Makefile
@@ -824,6 +824,7 @@ LIB_H := $(sort $(shell git ls-files '*.h' ':!t/' ':!Documentation/' 2>/dev/null
 	-name '*.h' -print))
 
 LIB_OBJS += abspath.o
+LIB_OBJS += add-interactive.o
 LIB_OBJS += advice.o
 LIB_OBJS += alias.o
 LIB_OBJS += alloc.o
diff --git a/add-interactive.c b/add-interactive.c
new file mode 100644
index 0000000000..482e458dc6
--- /dev/null
+++ b/add-interactive.c
@@ -0,0 +1,7 @@
+#include "cache.h"
+#include "add-interactive.h"
+
+int run_add_i(struct repository *r, const struct pathspec *ps)
+{
+	die(_("No commands are available in the built-in `git add -i` yet!"));
+}
diff --git a/add-interactive.h b/add-interactive.h
new file mode 100644
index 0000000000..7043b8741d
--- /dev/null
+++ b/add-interactive.h
@@ -0,0 +1,8 @@
+#ifndef ADD_INTERACTIVE_H
+#define ADD_INTERACTIVE_H
+
+struct repository;
+struct pathspec;
+int run_add_i(struct repository *r, const struct pathspec *ps);
+
+#endif
diff --git a/builtin/add.c b/builtin/add.c
index dd18e5c9b6..4f625691b5 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -20,6 +20,7 @@
 #include "bulk-checkin.h"
 #include "argv-array.h"
 #include "submodule.h"
+#include "add-interactive.h"
 
 static const char * const builtin_add_usage[] = {
 	N_("git add [<options>] [--] <pathspec>..."),
@@ -185,6 +186,14 @@ int run_add_interactive(const char *revision, const char *patch_mode,
 {
 	int status, i;
 	struct argv_array argv = ARGV_ARRAY_INIT;
+	int use_builtin_add_i =
+		git_env_bool("GIT_TEST_ADD_I_USE_BUILTIN", -1);
+	if (use_builtin_add_i < 0)
+		git_config_get_bool("add.interactive.usebuiltin",
+				    &use_builtin_add_i);
+
+	if (use_builtin_add_i == 1 && !patch_mode)
+		return !!run_add_i(the_repository, pathspec);
 
 	argv_array_push(&argv, "add--interactive");
 	if (patch_mode)
@@ -319,6 +328,7 @@ static int add_config(const char *var, const char *value, void *cb)
 		ignore_add_errors = git_config_bool(var, value);
 		return 0;
 	}
+
 	return git_default_config(var, value, cb);
 }
 
diff --git a/t/README b/t/README
index 9747971d58..28999cebd3 100644
--- a/t/README
+++ b/t/README
@@ -397,6 +397,10 @@ GIT_TEST_STASH_USE_BUILTIN=<boolean>, when false, disables the
 built-in version of git-stash. See 'stash.useBuiltin' in
 git-config(1).
 
+GIT_TEST_ADD_I_USE_BUILTIN=<boolean>, when true, enables the
+builtin version of git add -i. See 'add.interactive.useBuiltin' in
+git-config(1).
+
 GIT_TEST_INDEX_THREADS=<n> enables exercising the multi-threaded loading
 of the index for the whole test suite by bypassing the default number of
 cache entries and thread minimums. Setting this to 1 will make the

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