Merge branch 'dg/myfirstobjectwalk-updates'

Update a more recent tutorial doc.

* dg/myfirstobjectwalk-updates:
  MyFirstObjectWalk: add stderr to pipe processing
  MyFirstObjectWalk: fix description for counting omitted objects
  MyFirstObjectWalk: fix filtered object walk
  MyFirstObjectWalk: fix misspelled "builtins/"
  MyFirstObjectWalk: use additional arg in config_fn_t

Author: gitster

Documentation/MyFirstObjectWalk.txt

@@ -210,13 +210,14 @@ We'll also need to include the `config.h` header:
 
 ...
 
-static int git_walken_config(const char *var, const char *value, void *cb)
+static int git_walken_config(const char *var, const char *value,
+			     const struct config_context *ctx, void *cb)
 {
 	/*
 	 * For now, we don't have any custom configuration, so fall back to
 	 * the default config.
 	 */
-	return git_default_config(var, value, cb);
+	return git_default_config(var, value, ctx, cb);
 }
 ----
 
@@ -389,10 +390,11 @@ modifying `rev_info.grep_filter`, which is a `struct grep_opt`.
 First some setup. Add `grep_config()` to `git_walken_config()`:
 
 ----
-static int git_walken_config(const char *var, const char *value, void *cb)
+static int git_walken_config(const char *var, const char *value,
+			     const struct config_context *ctx, void *cb)
 {
-	grep_config(var, value, cb);
-	return git_default_config(var, value, cb);
+	grep_config(var, value, ctx, cb);
+	return git_default_config(var, value, ctx, cb);
 }
 ----
 
@@ -523,7 +525,7 @@ about each one.
 
 We can base our work on an example. `git pack-objects` prepares all kinds of
 objects for packing into a bitmap or packfile. The work we are interested in
-resides in `builtins/pack-objects.c:get_object_list()`; examination of that
+resides in `builtin/pack-objects.c:get_object_list()`; examination of that
 function shows that the all-object walk is being performed by
 `traverse_commit_list()` or `traverse_commit_list_filtered()`. Those two
 functions reside in `list-objects.c`; examining the source shows that, despite
@@ -732,8 +734,8 @@ walk we've just performed:
 	} else {
 		trace_printf(
 			_("Filtered object walk with filterspec 'tree:1'.\n"));
-		CALLOC_ARRAY(rev->filter, 1);
-		parse_list_objects_filter(rev->filter, "tree:1");
+
+		parse_list_objects_filter(&rev->filter, "tree:1");
 	}
 	traverse_commit_list(rev, walken_show_commit,
 			     walken_show_object, NULL);
@@ -752,10 +754,12 @@ points to the same tree object as its grandparent.)
 === Counting Omitted Objects
 
 We also have the capability to enumerate all objects which were omitted by a
-filter, like with `git log --filter=<spec> --filter-print-omitted`. Asking
-`traverse_commit_list_filtered()` to populate the `omitted` list means that our
-object walk does not perform any better than an unfiltered object walk; all
-reachable objects are walked in order to populate the list.
+filter, like with `git log --filter=<spec> --filter-print-omitted`. To do this,
+change `traverse_commit_list()` to `traverse_commit_list_filtered()`, which is
+able to populate an `omitted` list.  Asking for this list of filtered objects
+may cause performance degradations, however, because in this case, despite
+filtering objects, the possibly much larger set of all reachable objects must
+be processed in order to populate that list.
 
 First, add the `struct oidset` and related items we will use to iterate it:
 
@@ -776,8 +780,9 @@ static void walken_object_walk(
 	...
 ----
 
-Modify the call to `traverse_commit_list_filtered()` to include your `omitted`
-object:
+Replace the call to `traverse_commit_list()` with
+`traverse_commit_list_filtered()` and pass a pointer to the `omitted` oidset
+defined and initialized above:
 
 ----
 	...
@@ -843,7 +848,7 @@ those lines without having to recompile.
 With only that change, run again (but save yourself some scrollback):
 
 ----
-$ GIT_TRACE=1 ./bin-wrappers/git walken | head -n 10
+$ GIT_TRACE=1 ./bin-wrappers/git walken 2>&1 | head -n 10
 ----
 
 Take a look at the top commit with `git show` and the object ID you printed; it
@@ -871,7 +876,7 @@ of the first handful:
 
 ----
 $ make
-$ GIT_TRACE=1 ./bin-wrappers git walken | tail -n 10
+$ GIT_TRACE=1 ./bin-wrappers/git walken 2>&1 | tail -n 10
 ----
 
 The last commit object given should have the same OID as the one we saw at the