Re: [PATCH v2 08/14] commit-graph: implement git-commit-graph --clear

[SZEDER Gábor]

> Teach Git to delete the current 'graph_head' file and the commit graph
> it references.

And will it leave other, non-important graph files behind?  Looking at
the code it indeed does.  What is the use case for keeping the
non-important graph files?

> This is a good safety valve if somehow the file is
> corrupted and needs to be recalculated. Since the commit graph is a
> summary of contents already in the ODB, it can be regenerated.

Wouldn't a simple 'git commit-graph --write --update-head' regenerate
it on it's own, without cleaning first?  It appears, after running a
few tests, that a corrupt graph file can be recreated without
cleaning, which is great.  However, if graph-head is corrupt, then the
command errors out with 'failed to read graph-head'.  I don't
understand the rationale behind this, it would be overwritten anyway,
and its content is not necessary for recreating the graph.  And
indeed, after commenting out that get_graph_head_hash() call in
cmd_commit_graph() it doesn't want to read my corrupted graph-head
file, and recreates both the graph and graph-head files just fine.

I think the requirement for explicitly cleaning a corrupt graph-head
before re-writing it is just unnecessary complication.

On second thought, what's the point of '--write' without
'--update-head', when consumers (thinking 'log --topo-order...) will
need the graph-head anyway?  I think '--write' should create a
graph-head without requiring an additional option.

Hmph, another second thought: the word 'head' has a rather specific
meaning in Git, although it's usually capitalized.  Using this word in
options and filenames may lead to confusion, especially the option
'--update-head'.


> Signed-off-by: Derrick Stolee 
> ---
>  Documentation/git-commit-graph.txt | 16 ++--
>  builtin/commit-graph.c | 32 +++-
>  t/t5318-commit-graph.sh|  7 ++-
>  3 files changed, 51 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/git-commit-graph.txt 
> b/Documentation/git-commit-graph.txt
> index 99ced16ddc..33d6567f11 100644
> --- a/Documentation/git-commit-graph.txt
> +++ b/Documentation/git-commit-graph.txt
> @@ -11,6 +11,7 @@ SYNOPSIS
>  [verse]
>  'git commit-graph' --write  [--pack-dir ]
>  'git commit-graph' --read  [--pack-dir ]
> +'git commit-graph' --clear [--pack-dir ]
>  
>  OPTIONS
>  ---
> @@ -18,16 +19,21 @@ OPTIONS
>   Use given directory for the location of packfiles, graph-head,
>   and graph files.
>  
> +--clear::
> + Delete the graph-head file and the graph file it references.
> + (Cannot be combined with --read or --write.)
> +
>  --read::
>   Read a graph file given by the graph-head file and output basic
> - details about the graph file. (Cannot be combined with --write.)
> + details about the graph file. (Cannot be combined with --clear
> + or --write.)
>  
>  --graph-id::
>   When used with --read, consider the graph file graph-.graph.
>  
>  --write::
>   Write a new graph file to the pack directory. (Cannot be combined
> - with --read.)
> + with --clear or --read.)

All these "cannot be combined with --this and --that" remarks make
subcommands more and more appealing.

>  
>  --update-head::
>   When used with --write, update the graph-head file to point to
> @@ -61,6 +67,12 @@ $ git commit-graph --write --update-head
>  $ git commit-graph --read --graph-hash=
>  
>  
> +* Delete /graph-head and the file it references.
> ++
> +
> +$ git commit-graph --clear --pack-dir=
> +
> +
>  GIT
>  ---
>  Part of the linkgit:git[1] suite
> diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
> index d73cbc907d..4970dec133 100644
> --- a/builtin/commit-graph.c
> +++ b/builtin/commit-graph.c
> @@ -10,6 +10,7 @@
>  
>  static char const * const builtin_commit_graph_usage[] = {
>   N_("git commit-graph [--pack-dir ]"),
> + N_("git commit-graph --clear [--pack-dir ]"),
>   N_("git commit-graph --read [--graph-hash=]"),
>   N_("git commit-graph --write [--pack-dir ] [--update-head]"),
>   NULL
> @@ -17,6 +18,7 @@ static char const * const builtin_commit_graph_usage[] = {
>  
>  static struct opts_commit_graph {
>   const char *pack_dir;
> + int clear;
>   int read;
>   const char *graph_hash;
>   int write;
> @@ -25,6 +27,30 @@ static struct opts_commit_graph {
>   struct object_id old_graph_hash;
>  } opts;
>  
> +static int graph_clear(void)
> +{
> + struct strbuf head_path = STRBUF_INIT;
> + char *old_path;
> +
> + if (!opts.has_existing)
> + return 0;
> +
> + strbuf_addstr(_path, opts.pack_dir);
> + strbuf_addstr(_path, "/");
> + strbuf_addstr(_path, "graph-head");

strbuf_addstr(_path, "/graph-head")

Although, considering that this is 

[PATCH v2 08/14] commit-graph: implement git-commit-graph --clear

[Derrick Stolee]

Teach Git to delete the current 'graph_head' file and the commit graph
it references. This is a good safety valve if somehow the file is
corrupted and needs to be recalculated. Since the commit graph is a
summary of contents already in the ODB, it can be regenerated.

Signed-off-by: Derrick Stolee 
---
 Documentation/git-commit-graph.txt | 16 ++--
 builtin/commit-graph.c | 32 +++-
 t/t5318-commit-graph.sh|  7 ++-
 3 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-commit-graph.txt 
b/Documentation/git-commit-graph.txt
index 99ced16ddc..33d6567f11 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git commit-graph' --write  [--pack-dir ]
 'git commit-graph' --read  [--pack-dir ]
+'git commit-graph' --clear [--pack-dir ]
 
 OPTIONS
 ---
@@ -18,16 +19,21 @@ OPTIONS
Use given directory for the location of packfiles, graph-head,
and graph files.
 
+--clear::
+   Delete the graph-head file and the graph file it references.
+   (Cannot be combined with --read or --write.)
+
 --read::
Read a graph file given by the graph-head file and output basic
-   details about the graph file. (Cannot be combined with --write.)
+   details about the graph file. (Cannot be combined with --clear
+   or --write.)
 
 --graph-id::
When used with --read, consider the graph file graph-.graph.
 
 --write::
Write a new graph file to the pack directory. (Cannot be combined
-   with --read.)
+   with --clear or --read.)
 
 --update-head::
When used with --write, update the graph-head file to point to
@@ -61,6 +67,12 @@ $ git commit-graph --write --update-head
 $ git commit-graph --read --graph-hash=
 
 
+* Delete /graph-head and the file it references.
++
+
+$ git commit-graph --clear --pack-dir=
+
+
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index d73cbc907d..4970dec133 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -10,6 +10,7 @@
 
 static char const * const builtin_commit_graph_usage[] = {
N_("git commit-graph [--pack-dir ]"),
+   N_("git commit-graph --clear [--pack-dir ]"),
N_("git commit-graph --read [--graph-hash=]"),
N_("git commit-graph --write [--pack-dir ] [--update-head]"),
NULL
@@ -17,6 +18,7 @@ static char const * const builtin_commit_graph_usage[] = {
 
 static struct opts_commit_graph {
const char *pack_dir;
+   int clear;
int read;
const char *graph_hash;
int write;
@@ -25,6 +27,30 @@ static struct opts_commit_graph {
struct object_id old_graph_hash;
 } opts;
 
+static int graph_clear(void)
+{
+   struct strbuf head_path = STRBUF_INIT;
+   char *old_path;
+
+   if (!opts.has_existing)
+   return 0;
+
+   strbuf_addstr(_path, opts.pack_dir);
+   strbuf_addstr(_path, "/");
+   strbuf_addstr(_path, "graph-head");
+   if (remove_path(head_path.buf))
+   die("failed to remove path %s", head_path.buf);
+   strbuf_release(_path);
+
+   old_path = get_commit_graph_filename_hash(opts.pack_dir,
+ _graph_hash);
+   if (remove_path(old_path))
+   die("failed to remove path %s", old_path);
+   free(old_path);
+
+   return 0;
+}
+
 static int graph_read(void)
 {
struct object_id graph_hash;
@@ -105,6 +131,8 @@ int cmd_commit_graph(int argc, const char **argv, const 
char *prefix)
{ OPTION_STRING, 'p', "pack-dir", _dir,
N_("dir"),
N_("The pack directory to store the graph") },
+   OPT_BOOL('c', "clear", ,
+   N_("clear graph file and graph-head")),
OPT_BOOL('r', "read", ,
N_("read graph file")),
OPT_BOOL('w', "write", ,
@@ -126,7 +154,7 @@ int cmd_commit_graph(int argc, const char **argv, const 
char *prefix)
 builtin_commit_graph_options,
 builtin_commit_graph_usage, 0);
 
-   if (opts.write + opts.read > 1)
+   if (opts.write + opts.read + opts.clear > 1)
usage_with_options(builtin_commit_graph_usage,
   builtin_commit_graph_options);
 
@@ -139,6 +167,8 @@ int cmd_commit_graph(int argc, const char **argv, const 
char *prefix)
 
opts.has_existing = !!get_graph_head_hash(opts.pack_dir, 
_graph_hash);
 
+   if (opts.clear)
+   return graph_clear();
if (opts.read)
return graph_read();
if (opts.write)
diff --git