Re: [PATCH v2 1/3] patch-id: make it stable against hunk reordering

Junio C Hamano [off-list ref] writes:

quoted

@@ -99,6 +116,18 @@ static int get_one_patchid(unsigned char *next_sha1, git_SHA_CTX *ctx, struct st
 			if (!memcmp(line, "@@ -", 4)) {
 				/* Parse next hunk, but ignore line numbers.  */
 				scan_hunk_header(line, &before, &after);
+				if (stable) {
+					if (hunks) {
+						flush_one_hunk(result, &ctx);
+						memcpy(&ctx, &header_ctx,
+						       sizeof ctx);
+					} else {
+						/* Save ctx for next hunk.  */
+						memcpy(&header_ctx, &ctx,
+						       sizeof ctx);
+					}
+				}
+				hunks++;
 				continue;
 			}
 

@@ -107,7 +136,10 @@ static int get_one_patchid(unsigned char *next_sha1, git_SHA_CTX *ctx, struct st
 				break;
 
 			/* Else we're parsing another header.  */
+			if (stable && hunks)
+				flush_one_hunk(result, &ctx);
 			before = after = -1;
+			hunks = 0;
 		}
 
 		/* If we get here, we're inside a hunk.  */

@@ -119,39 +151,46 @@ static int get_one_patchid(unsigned char *next_sha1, git_SHA_CTX *ctx, struct st
 		/* Compute the sha without whitespace */
 		len = remove_space(line);
 		patchlen += len;
-		git_SHA1_Update(ctx, line, len);
+		git_SHA1_Update(&ctx, line, len);
 	}
 
 	if (!found_next)
 		hashclr(next_sha1);
 
+	flush_one_hunk(result, &ctx);

What I read from these changes is that you do not do anything
special about the per-file header, so two no overlapping patches
with a single hunk each that touches the same path concatenated
together would not result in the same patch-id as a single-patch
that has the same two hunks.  Which would break your earlier 'Yes,
reordering only the hunks will not make sense, but before each hunk
you could insert the same "diff --git a/... b/..." to make them a
concatenation of patches that touch the same file', I would think.

Is that what we want to happen?  Or is my reading mistaken?

Heh, I was blind---copying into header_ctx and then restoring that
in preparation for the next round is exactly for duplicating the
per-file header sum to each and every hunk, so you are already doing
that.