treewide: custom reasons for expanding index

These cases that call ensure_full_index() are likely to be due to a data
shape issue on a user's machine, so take the extra time to format a
message that can be placed in their trace2 output and hopefully identify
the problem that is leading to this slow behavior.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: derrickstolee

builtin/update-index.c

@@ -714,7 +714,9 @@ static int do_reupdate(const char **paths,
 		 * to process each path individually
 		 */
 		if (S_ISSPARSEDIR(ce->ce_mode)) {
-			ensure_full_index(the_repository->index);
+			const char *fmt = "update-index:modified sparse dir '%s'";
+			ensure_full_index_with_reason(the_repository->index,
+						      fmt, ce->name);
 			goto redo;
 		}
 

merge-ort.c

@@ -4569,7 +4569,8 @@ static int record_conflicted_index_entries(struct merge_options *opt)
 	 */
 	strmap_for_each_entry(&opt->priv->conflicted, &iter, e) {
 		if (!path_in_sparse_checkout(e->key, index)) {
-			ensure_full_index(index);
+			const char *fmt = "merge-ort: path outside sparse checkout (%s)";
+			ensure_full_index_with_reason(index, fmt, e->key);
 			break;
 		}
 	}

read-cache.c

@@ -555,7 +555,9 @@ static int index_name_stage_pos(struct index_state *istate,
 		if (S_ISSPARSEDIR(ce->ce_mode) &&
 		    ce_namelen(ce) < namelen &&
 		    !strncmp(name, ce->name, ce_namelen(ce))) {
-			ensure_full_index(istate);
+			const char *fmt = "searching for '%s' and found parent dir '%s'";
+			ensure_full_index_with_reason(istate, fmt,
+						      name, ce->name);
 			return index_name_stage_pos(istate, name, namelen, stage, search_mode);
 		}
 	}

sparse-index.c

@@ -758,7 +758,9 @@ void expand_to_path(struct index_state *istate,
 			 * in the index, perhaps it exists within this
 			 * sparse-directory.  Expand accordingly.
 			 */
-			ensure_full_index(istate);
+			const char *fmt = "found index entry for '%s'";
+			ensure_full_index_with_reason(istate, fmt,
+						      path_mutable.buf);
 			break;
 		}
 

t/t1092-sparse-checkout-compatibility.sh

@@ -2654,7 +2654,15 @@ test_expect_success 'ensure_full_index_with_reason' '
 
 	GIT_TRACE2_EVENT="$(pwd)/ls-files-trace" \
 		git -C sparse-index ls-files --no-sparse HEAD &&
-	test_trace2_data "sparse-index" "expansion-reason" "ls-files" <ls-files-trace
+	test_trace2_data "sparse-index" "expansion-reason" "ls-files" <ls-files-trace &&
+
+	mkdir -p sparse-index/folder2 &&
+	echo >sparse-index/folder2/a &&
+	GIT_TRACE2_EVENT="$(pwd)/status-trace" \
+		git -C sparse-index status &&
+	test_trace2_data "sparse-index" "skip-worktree sparsedir" "folder2/" <status-trace &&
+	test_trace2_data "sparse-index" "expansion-reason" \
+		"failed to clear skip-worktree while sparse" <status-trace
 '
 
 test_done

unpack-trees.c

@@ -1893,8 +1893,10 @@ static void update_sparsity_for_prefix(const char *prefix,
 	 *   the 'ensure_full_index(...)' below.
 	 */
 	if (!path_in_cone_mode_sparse_checkout(ce_prefix.buf, istate) &&
-	    index_name_pos(istate, ce_prefix.buf, ce_prefix.len) >= 0)
-		ensure_full_index(istate);
+	    index_name_pos(istate, ce_prefix.buf, ce_prefix.len) >= 0) {
+		const char *fmt = "could not find '%s' in index";
+		ensure_full_index_with_reason(istate, fmt, ce_prefix.buf);
+	}
 
 	strbuf_release(&ce_prefix);
 }