Make 'got status' compare the file size recorded in the file index to
the size of the on-disk file, before running a full content comparison.
Skip the full content comparison loop if the sizes differ.

Speeds up 'got status' in work trees that contain large modified files.
This speed-up is not very significant because we still compute diffs in
order to detect conflicts (by looking for conflict markers on newly added
lines). Which means large files will still be read anyway in order to
compare them to their base blob. But at least this avoids reading such
files twice in a row.

More interestingly, this change exposes bugs in 'got revert' which manifest
as test failures.
One bug where the size recorded in the file index is not updated during
revert, and another where a wrong base commit is recorded in the file
index entry during revert. Fix those bugs, too.
To see the relevant test failures run 'make regress' without the changes
to the revert_file() function below.

ok?

M  lib/worktree.c  |  25+  9-

1 file changed, 25 insertions(+), 9 deletions(-)

commit - 34b2702155c3b2f22d92d76d2f807e818ad5789f
commit + f6dff504a5361205afd9d92e015dd00dd8b8da60
blob - df89f493b283c3c8957846b5f60994c98756d8ae
blob + 71a215359b98caf08ed6fafa8841fdd8dbd4caac
--- lib/worktree.c
+++ lib/worktree.c
@@ -1839,8 +1839,22 @@ get_file_status(unsigned char *status, struct stat *sb
 		goto done;
 	}
 	fd = -1;
+
+	if (staged_status == GOT_STATUS_NO_CHANGE &&
+	    S_ISREG(sb->st_mode) &&
+	    got_fileindex_entry_filetype_get(ie) ==
+	    GOT_FILEIDX_MODE_REGULAR_FILE &&
+	    ie->size != (sb->st_size & 0xffffffff)) {
+		/*
+		 * The size of regular files differs. We can skip the full
+		 * content comparison loop below but still need to check
+		 * for conflict markers.
+		 */
+		*status = GOT_STATUS_MODIFY;
+	}
+
 	hdrlen = got_object_blob_get_hdrlen(blob);
-	for (;;) {
+	while (*status == GOT_STATUS_NO_CHANGE) {
 		const uint8_t *bbuf = got_object_blob_get_read_buf(blob);
 		err = got_object_blob_read_block(&blen, blob);
 		if (err)
@@ -5355,6 +5369,11 @@ revert_file(void *arg, unsigned char status, unsigned 
 					goto done;
 				}
 			}
+			err = got_fileindex_entry_update(ie,
+			    a->worktree->root_fd, relpath,
+			    &blob->id, &ie->commit, 0);
+			if (err)
+				goto done;
 		} else {
 			int is_bad_symlink = 0;
 			if (te && S_ISLNK(te->mode)) {
@@ -5372,14 +5391,11 @@ revert_file(void *arg, unsigned char status, unsigned 
 			}
 			if (err)
 				goto done;
-			if (status == GOT_STATUS_DELETE ||
-			    status == GOT_STATUS_MODE_CHANGE) {
-				err = got_fileindex_entry_update(ie,
-				    a->worktree->root_fd, relpath,
-				    &blob->id, a->worktree->base_commit_id, 1);
-				if (err)
-					goto done;
-			}
+			err = got_fileindex_entry_update(ie,
+			    a->worktree->root_fd, relpath,
+			    &blob->id, &ie->commit, 0);
+			if (err)
+				goto done;
 			if (is_bad_symlink) {
 				got_fileindex_entry_filetype_set(ie,
 				    GOT_FILEIDX_MODE_BAD_SYMLINK);