[PATCH] Introducing software archaeologist's tool "pickaxe".

This steals the "pickaxe" feature from JIT and make it available
to the bare Plumbing layer.  From the command line, the user
gives a string he is intersted in.

Using the diff-core infrastructure previously introduced, it
filters the differences to limit the output only to the diffs
between <src> and <dst> where the string appears only in one but
not in the other.  For example:

 $ ./git-rev-list HEAD | ./git-diff-tree -Sdiff-tree-helper --stdin -M

would show the diffs that touch the string "diff-tree-helper".

In real software-archaeologist application, you would typically
look for a few to several lines of code and see where that code
came from.

The "pickaxe" module runs after "rename/copy detection" module,
so it even crosses the file rename boundary, as the above
example demonstrates.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

4 files changed, 19 insertions, 4 deletions

diff --git a/Documentation/git-diff-cache.txt b/Documentation/git-diff-cache.txt
index e3ed7131a..2cfdffd87 100644
--- a/Documentation/git-diff-cache.txt
+++ b/Documentation/git-diff-cache.txt
@@ -9,7 +9,7 @@ git-diff-cache - Compares content and mode of blobs between the cache and reposi
 
 SYNOPSIS
 --------
-'git-diff-cache' [-p] [-r] [-z] [-m] [-M] [-R] [-C] [--cached] <tree-ish>
+'git-diff-cache' [-p] [-r] [-z] [-m] [-M] [-R] [-C] [-S<string>] [--cached] <tree-ish>
 
 DESCRIPTION
 -----------
@@ -39,6 +39,10 @@ OPTIONS
 -C::
 	Detect copies as well as renames; implies -p.
 
+-S<string>::
+	Look for differences that contains the change in <string>.
+
+
 -R::
 	Output diff in reverse.
 
diff --git a/Documentation/git-diff-files.txt b/Documentation/git-diff-files.txt
index 1eae3d033..51a3d0fcd 100644
--- a/Documentation/git-diff-files.txt
+++ b/Documentation/git-diff-files.txt
@@ -9,7 +9,7 @@ git-diff-files - Compares files in the working tree and the cache
 
 SYNOPSIS
 --------
-'git-diff-files' [-p] [-q] [-r] [-z] [-M] [-C] [-R] [<pattern>...]
+'git-diff-files' [-p] [-q] [-r] [-z] [-M] [-C] [-R] [-S<string>] [<pattern>...]
 
 DESCRIPTION
 -----------
@@ -35,6 +35,10 @@ OPTIONS
 -C::
 	Detect copies as well as renames; implies -p.
 
+-S<string>::
+	Look for differences that contains the change in <string>.
+
+
 -r::
 	This flag does not mean anything.  It is there only to match
 	git-diff-tree.  Unlike git-diff-tree, git-diff-files always looks
diff --git a/Documentation/git-diff-helper.txt b/Documentation/git-diff-helper.txt
index 302789e9d..2036c6cc1 100644
--- a/Documentation/git-diff-helper.txt
+++ b/Documentation/git-diff-helper.txt
@@ -9,7 +9,7 @@ git-diff-helper - Generates patch format output for git-diff-*
 
 SYNOPSIS
 --------
-'git-diff-helper' [-z] [-R] [-M] [-C]
+'git-diff-helper' [-z] [-R] [-M] [-C] [-S<string>]
 
 DESCRIPTION
 -----------
@@ -37,6 +37,10 @@ OPTIONS
 -C::
 	Detect copies as well as renames.
 
+-S<string>::
+	Look for differences that contains the change in <string>.
+
+
 See Also
 --------
 The section on generating patches in link:git-diff-cache.html[git-diff-cache]
diff --git a/Documentation/git-diff-tree.txt b/Documentation/git-diff-tree.txt
index f4e95a97c..bdc8d5a53 100644
--- a/Documentation/git-diff-tree.txt
+++ b/Documentation/git-diff-tree.txt
@@ -9,7 +9,7 @@ git-diff-tree - Compares the content and mode of blobs found via two tree object
 
 SYNOPSIS
 --------
-'git-diff-tree' [-p] [-r] [-z] [--stdin] [-M] [-R] [-C] [-m] [-s] [-v] <tree-ish> <tree-ish> [<pattern>]\*
+'git-diff-tree' [-p] [-r] [-z] [--stdin] [-M] [-R] [-C] [-S<string>] [-m] [-s] [-v] <tree-ish> <tree-ish> [<pattern>]\*
 
 DESCRIPTION
 -----------
@@ -43,6 +43,9 @@ OPTIONS
 -R::
 	Output diff in reverse.
 
+-S<string>::
+	Look for differences that contains the change in <string>.
+
 -r::
 	recurse