Re: [PATCH] revision: replace "struct cmdline_pathspec" with argv_array

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Sep 21, 2017, 04:41 UTC
Message-ID: <20170921044112.GB91069@aiede.mtv.corp.google.com>
In-Reply-To: <20170921030424.akqaou7tqj2updgr@sigill.intra.peff.net>

Jeff King wrote:

> On Wed, Sep 20, 2017 at 03:48:26PM -0700, Jonathan Nieder wrote:
>> Jeff King wrote:

Show 10 quoted lines

>>> Subject: [PATCH] revision: replace "struct cmdline_pathspec" with argv_array
>>>
>>> We assemble an array of strings in a custom struct,
>>> NULL-terminate the result, and then pass it to
>>> parse_pathspec().
>>>
>>> But then we never free the array or the individual strings
>>> (nor can we do the latter, as they are heap-allocated when
>>> they come from stdin but not when they come from the
>>> passed-in argv).

[...]

Show 7 quoted lines

>> Except... is the idea that this allows the strings from stdin to be
>> freed sooner, as soon as they have been parsed into a "struct
>> pathspec"?
>
> Well, no...the idea is that this is a function which leaks a bunch of
> memory, and we shouldn't have to think hard about how often its leak can
> be triggered or how severe it is. We should just fix it.

I forgot to say: thanks for writing such a pleasant patch.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>

[...]

> I certainly agree that the pathspec interface could use better
> documentation. Patches welcome? :)

Here's such a patch.

-- 8< --
Subject: pathspec doc: parse_pathspec does not maintain references to args

The command line arguments passed to main() are valid for the life of a program, but the same is not true for all other argv-style arrays (e.g. when a caller creates an argv_array). Clarify that parse_pathspec does not rely on the argv passed to it to remain valid.

This makes it easier to tell that callers like "git rev-list --stdin" are safe and ensures that that is more likely to remain true as the implementation of parse_pathspec evolves.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 pathspec.c | 4 ----
 pathspec.h | 7 +++++++
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/pathspec.c b/pathspec.c
index e2a23ebc96..cdefdc7cc0 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -526,10 +526,6 @@ static void NORETURN unsupported_magic(const char *pattern,
 	    pattern, sb.buf);
 }
 
-/*
- * Given command line arguments and a prefix, convert the input to
- * pathspec. die() if any magic in magic_mask is used.
- */
 void parse_pathspec(struct pathspec *pathspec,
 		    unsigned magic_mask, unsigned flags,
 		    const char *prefix, const char **argv)
diff --git a/pathspec.h b/pathspec.h
index 60e6500401..6420d1080a 100644
--- a/pathspec.h
+++ b/pathspec.h
@@ -70,6 +70,13 @@ struct pathspec {
  */
 #define PATHSPEC_LITERAL_PATH (1<<6)
 
+/*
+ * Given command line arguments and a prefix, convert the input to
+ * pathspec. die() if any magic in magic_mask is used.
+ *
+ * Any arguments used are copied. It is safe for the caller to modify
+ * or free 'prefix' and 'args' after calling this function.
+ */
 extern void parse_pathspec(struct pathspec *pathspec,
 			   unsigned magic_mask,
 			   unsigned flags,

-- 
2.14.1.821.g8fa685d3b7