[PATCH v4 0/2] Improve diffcore-pickaxe documentation

[PATCH v4 0/2] Improve diffcore-pickaxe documentation

[Ramkumar Ramachandra]

Junio had some suggestions in the previous round.  The inter-diff
follows.

Yeah, word-diff is a bit messy.  Which brings me to: is it possible to
turn on word-diff only where heuristically appropriate?  word-diff
applied on the rewrite of the first paragraph of gitdiffcore.txt is a
disaster, but okay everywhere else.

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index efb5dfe..a85288f 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -387,11 +387,11 @@ ifndef::git-format-patch[]
	the specified string (i.e. addition/deletion) in a file.
	Intended for the scripter's use.
+
It is[-especially-] useful when you're looking for an exact block of code (like a
struct), and want to know the history of that block since it first
came into being: use the feature iteratively to feed the interesting
block in the preimage back into `-S`, and keep going until you get the
very first version of the block.

-G<regex>::
	Look for differences whose patch text contains added/removed
diff --git a/Documentation/gitdiffcore.txt b/Documentation/gitdiffcore.txt
index ef4c04a..c8b3e51 100644
--- a/Documentation/gitdiffcore.txt
+++ b/Documentation/gitdiffcore.txt
@@ -222,25 +222,27 @@ version prefixed with '+'.
diffcore-pickaxe: For Detecting Addition/Deletion of Specified String
---------------------------------------------------------------------

[-There are two kinds of pickaxe:-]{+This transformation limits+} the [-S kind (corresponding-]{+set of filepairs+} to [-'git log-]
[--S')-]{+those that change+}
{+specified strings between the preimage+} and the [-G kind (mnemonic: grep; corresponding-]{+postimage in a certain+}
{+way.  -S<block of text> and -G<regular expression> options are used+} to
[-'git log -G').-]{+specify different ways these strings are sought.+}

"-S<block of text>" detects filepairs whose preimage and postimage
have different number of occurrences of the specified block of text.
By definition, it will not detect in-file moves.  Also, when a
changeset moves a file wholesale without affecting the interesting
string, [-rename detection-]{+diffcore-rename+} kicks in as usual, and `-S` omits the filepair
(since the number of occurrences of that string didn't change in that
rename-detected filepair).[-The implementation essentially-]
[-runs a count, and is significantly cheaper than the G kind.-]  When used with `--pickaxe-regex`, treat
the <block of text> as an extended POSIX regular expression to match,
instead of a literal string.

"-G<regular expression>" {+(mnemonic: grep)+} detects filepairs whose
textual diff has an added or a deleted line that matches the given
regular expression.  This means that it [-can-]{+will+} detect in-file (or what
rename-detection considers the same file) [-moves.-]{+moves, which is noise.+}  The
implementation runs diff twice and greps, and this can be quite
expensive.

When `-S` or `-G` are used without `--pickaxe-all`, only filepairs
that match their respective criterion are kept in the output.  When


Ramkumar Ramachandra (2):
  diffcore-pickaxe: make error messages more consistent
  diffcore-pickaxe doc: document -S and -G properly

 Documentation/diff-options.txt | 38 +++++++++++++++++++++++++++--------
 Documentation/gitdiffcore.txt  | 45 +++++++++++++++++++++++++-----------------
 diffcore-pickaxe.c             |  4 ++--
 3 files changed, 59 insertions(+), 28 deletions(-)

-- 
1.8.3.114.gcd03571

[PATCH 1/2] diffcore-pickaxe: make error messages more consistent

[Ramkumar Ramachandra]

Currently, diffcore-pickaxe reports two distinct errors for the same
user error:

    $ git log --pickaxe-regex -S'\1'
    fatal: invalid pickaxe regex: Invalid back reference

    $ git log -G'\1' # --pickaxe-regex is implied
    fatal: invalid log-grep regex: Invalid back reference

Since the error has nothing to do with "log-grep", change the -G and -S
error messages to say "invalid regex".

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 diffcore-pickaxe.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index 63722f8..c97ac9b 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -122,7 +122,7 @@ static void diffcore_pickaxe_grep(struct diff_options *o)
 		char errbuf[1024];
 		regerror(err, &regex, errbuf, 1024);
 		regfree(&regex);
-		die("invalid log-grep regex: %s", errbuf);
+		die("invalid regex: %s", errbuf);
 	}
 
 	pickaxe(&diff_queued_diff, o, &regex, NULL, diff_grep);
@@ -246,7 +246,7 @@ static void diffcore_pickaxe_count(struct diff_options *o)
 			char errbuf[1024];
 			regerror(err, &regex, errbuf, 1024);
 			regfree(&regex);
-			die("invalid pickaxe regex: %s", errbuf);
+			die("invalid regex: %s", errbuf);
 		}
 		regexp = &regex;
 	} else {
-- 
1.8.3.114.gcd03571

[PATCH 2/2] diffcore-pickaxe doc: document -S and -G properly

[Ramkumar Ramachandra]

The documentation of -S and -G is very sketchy.  Completely rewrite the
sections in Documentation/diff-options.txt and
Documentation/gitdiffcore.txt.

References:
52e9578 ([PATCH] Introducing software archaeologist's tool "pickaxe".)
f506b8e (git log/diff: add -G<regexp> that greps in the patch text)

Inputs-from: Phil Hord <phil.hord@gmail.com>
Co-authored-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 Documentation/diff-options.txt | 38 +++++++++++++++++++++++++++--------
 Documentation/gitdiffcore.txt  | 45 +++++++++++++++++++++++++-----------------
 2 files changed, 57 insertions(+), 26 deletions(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index b8a9b86..a85288f 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -383,14 +383,36 @@ ifndef::git-format-patch[]
 	that matches other criteria, nothing is selected.
 
 -S<string>::
-	Look for differences that introduce or remove an instance of
-	<string>. Note that this is different than the string simply
-	appearing in diff output; see the 'pickaxe' entry in
-	linkgit:gitdiffcore[7] for more details.
+	Look for differences that change the number of occurrences of
+	the specified string (i.e. addition/deletion) in a file.
+	Intended for the scripter's use.
++
+It is useful when you're looking for an exact block of code (like a
+struct), and want to know the history of that block since it first
+came into being: use the feature iteratively to feed the interesting
+block in the preimage back into `-S`, and keep going until you get the
+very first version of the block.
 
 -G<regex>::
-	Look for differences whose added or removed line matches
-	the given <regex>.
+	Look for differences whose patch text contains added/removed
+	lines that match <regex>.
++
+To illustrate the difference between `-S<regex> --pickaxe-regex` and
+`-G<regex>`, consider a commit with the following diff in the same
+file:
++
+----
++    return !regexec(regexp, two->ptr, 1, &regmatch, 0);
+...
+-    hit = !regexec(regexp, mf2.ptr, 1, &regmatch, 0);
+----
++
+While `git log -G"regexec\(regexp"` will show this commit, `git log
+-S"regexec\(regexp" --pickaxe-regex` will not (because the number of
+occurrences of that string did not change).
++
+See the 'pickaxe' entry in linkgit:gitdiffcore[7] for more
+information.
 
 --pickaxe-all::
 	When `-S` or `-G` finds a change, show all the changes in that
@@ -398,8 +420,8 @@ ifndef::git-format-patch[]
 	in <string>.
 
 --pickaxe-regex::
-	Make the <string> not a plain string but an extended POSIX
-	regex to match.
+	Treat the <string> given to `-S` as an extended POSIX regular
+	expression to match.
 endif::git-format-patch[]
 
 -O<orderfile>::
diff --git a/Documentation/gitdiffcore.txt b/Documentation/gitdiffcore.txt
index 568d757..c8b3e51 100644
--- a/Documentation/gitdiffcore.txt
+++ b/Documentation/gitdiffcore.txt
@@ -222,26 +222,35 @@ version prefixed with '+'.
 diffcore-pickaxe: For Detecting Addition/Deletion of Specified String
 ---------------------------------------------------------------------
 
-This transformation is used to find filepairs that represent
-changes that touch a specified string, and is controlled by the
--S option and the `--pickaxe-all` option to the 'git diff-*'
-commands.
-
-When diffcore-pickaxe is in use, it checks if there are
-filepairs whose "result" side and whose "origin" side have
-different number of specified string.  Such a filepair represents
-"the string appeared in this changeset".  It also checks for the
-opposite case that loses the specified string.
-
-When `--pickaxe-all` is not in effect, diffcore-pickaxe leaves
-only such filepairs that touch the specified string in its
-output.  When `--pickaxe-all` is used, diffcore-pickaxe leaves all
-filepairs intact if there is such a filepair, or makes the
-output empty otherwise.  The latter behaviour is designed to
-make reviewing of the changes in the context of the whole
+This transformation limits the set of filepairs to those that change
+specified strings between the preimage and the postimage in a certain
+way.  -S<block of text> and -G<regular expression> options are used to
+specify different ways these strings are sought.
+
+"-S<block of text>" detects filepairs whose preimage and postimage
+have different number of occurrences of the specified block of text.
+By definition, it will not detect in-file moves.  Also, when a
+changeset moves a file wholesale without affecting the interesting
+string, diffcore-rename kicks in as usual, and `-S` omits the filepair
+(since the number of occurrences of that string didn't change in that
+rename-detected filepair).  When used with `--pickaxe-regex`, treat
+the <block of text> as an extended POSIX regular expression to match,
+instead of a literal string.
+
+"-G<regular expression>" (mnemonic: grep) detects filepairs whose
+textual diff has an added or a deleted line that matches the given
+regular expression.  This means that it will detect in-file (or what
+rename-detection considers the same file) moves, which is noise.  The
+implementation runs diff twice and greps, and this can be quite
+expensive.
+
+When `-S` or `-G` are used without `--pickaxe-all`, only filepairs
+that match their respective criterion are kept in the output.  When
+`--pickaxe-all` is used, if even one filepair matches their respective
+criterion in a changeset, the entire changeset is kept.  This behavior
+is designed to make reviewing changes in the context of the whole
 changeset easier.
 
-
 diffcore-order: For Sorting the Output Based on Filenames
 ---------------------------------------------------------
 
-- 
1.8.3.114.gcd03571

Re: [PATCH 1/2] diffcore-pickaxe: make error messages more consistent

[Junio C Hamano]

Ramkumar Ramachandra <artagnon@gmail.com> writes:

> Currently, diffcore-pickaxe reports two distinct errors for the same
> user error:
>
>     $ git log --pickaxe-regex -S'\1'
>     fatal: invalid pickaxe regex: Invalid back reference
>
>     $ git log -G'\1' # --pickaxe-regex is implied
>     fatal: invalid log-grep regex: Invalid back reference
>
> Since the error has nothing to do with "log-grep", change the -G and -S
> error messages to say "invalid regex".

I'll reword the above somewhat; as I repeatedly explained, -G does
*not* imply pickaxe-regex at all.

While -G was being developed, it was internally called log-grep (no
relation to "git log --grep=<pattern>"), and that seeped through to
the error message.  Removing that is a good idea.

Thanks, will queue.



>
> Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
> ---
>  diffcore-pickaxe.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
> index 63722f8..c97ac9b 100644
> --- a/diffcore-pickaxe.c
> +++ b/diffcore-pickaxe.c
> @@ -122,7 +122,7 @@ static void diffcore_pickaxe_grep(struct diff_options *o)
>  		char errbuf[1024];
>  		regerror(err, &regex, errbuf, 1024);
>  		regfree(&regex);
> -		die("invalid log-grep regex: %s", errbuf);
> +		die("invalid regex: %s", errbuf);
>  	}
>  
>  	pickaxe(&diff_queued_diff, o, &regex, NULL, diff_grep);
> @@ -246,7 +246,7 @@ static void diffcore_pickaxe_count(struct diff_options *o)
>  			char errbuf[1024];
>  			regerror(err, &regex, errbuf, 1024);
>  			regfree(&regex);
> -			die("invalid pickaxe regex: %s", errbuf);
> +			die("invalid regex: %s", errbuf);
>  		}
>  		regexp = &regex;
>  	} else {

Re: [PATCH 2/2] diffcore-pickaxe doc: document -S and -G properly

[Junio C Hamano]

Ramkumar Ramachandra <artagnon@gmail.com> writes:

> The documentation of -S and -G is very sketchy.  Completely rewrite the
> sections in Documentation/diff-options.txt and
> Documentation/gitdiffcore.txt.

Will queue; thanks.