Fix mishandling of $Id$ expanded in the repository copy in convert.c

If the repository contained an expanded ident keyword (i.e. $Id:XXXX$),
then the wrong bytes were discarded, and the Id keyword was not
expanded.  The fault was in convert.c:ident_to_worktree().

Previously, when a "$Id:" was found in the repository version,
ident_to_worktree() would search for the next "$" after this, and
discarded everything it found until then.  That was done with the loop:

    do {
        ch = *cp++;
        if (ch == '$')
            break;
        rem--;
    } while (rem);

The above loop left cp pointing one character _after_ the final "$"
(because of ch = *cp++).  This was different from the non-expanded case,
were cp is left pointing at the "$", and was different from the comment
which stated "discard up to but not including the closing $".  This
patch fixes that by making the loop:

    do {
        ch = *cp;
        if (ch == '$')
            break;
        cp++;
        rem--;
    } while (rem);

That is, cp is tested _then_ incremented.

This loop exits if it finds a "$" or if it runs out of bytes in the
source.  After this loop, if there was no closing "$" the expansion is
skipped, and the outer loop is allowed to continue leaving this
non-keyword as it was.  However, when the "$" is found, size is
corrected, before running the expansion:

    size -= (cp - src);

This is wrong; size is going to be corrected anyway after the expansion,
so there is no need to do it here.  This patch removes that redundant
correction.

To help find this bug, I heavily commented the routine; those comments
are included here as a bonus.

Signed-off-by: Andy Parkins <andyparkins@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/convert.c b/convert.c
index 4b26b1a9b9979c2a7753afdad107c73f3e1aae4c..21908b10398492c0b07f705ed3b1ce7a06ac6b44 100644 (file)
--- a/convert.c
+++ b/convert.c
@@ -509,36 +509,71 @@ static char *ident_to_worktree(const char *path, const char *src, unsigned long
 
        for (dst = buf; size; size--) {
                const char *cp;
+               /* Fetch next source character, move the pointer on */
                char ch = *src++;
+               /* Copy the current character to the destination */
                *dst++ = ch;
+               /* If the current character is "$" or there are less than three
+                * remaining bytes or the two bytes following this one are not
+                * "Id", then simply read the next character */
                if ((ch != '$') || (size < 3) || memcmp("Id", src, 2))
                        continue;
+               /*
+                * Here when
+                *  - There are more than 2 bytes remaining
+                *  - The current three bytes are "$Id"
+                * with
+                *  - ch == "$"
+                *  - src[0] == "I"
+                */
 
+               /*
+                * It's possible that an expanded Id has crept its way into the
+                * repository, we cope with that by stripping the expansion out
+                */
                if (src[2] == ':') {
+                       /* Expanded keywords have "$Id:" at the front */
+
                        /* discard up to but not including the closing $ */
                        unsigned long rem = size - 3;
+                       /* Point at first byte after the ":" */
                        cp = src + 3;
+                       /*
+                        * Throw away characters until either
+                        *  - we reach a "$"
+                        *  - we run out of bytes (rem == 0)
+                        */
                        do {
-                               ch = *cp++;
+                               ch = *cp;
                                if (ch == '$')
                                        break;
+                               cp++;
                                rem--;
                        } while (rem);
+                       /* If the above finished because it ran out of characters, then
+                        * this is an incomplete keyword, so don't run the expansion */
                        if (!rem)
                                continue;
-                       size -= (cp - src);
                } else if (src[2] == '$')
                        cp = src + 2;
                else
+                       /* Anything other than "$Id:XXX$" or $Id$ and we skip the
+                        * expansion */
                        continue;
 
+               /* cp is now pointing at the last $ of the keyword */
+
                memcpy(dst, "Id: ", 4);
                dst += 4;
                memcpy(dst, sha1_to_hex(sha1), 40);
                dst += 40;
                *dst++ = ' ';
+
+               /* Adjust for the characters we've discarded */
                size -= (cp - src);
                src = cp;
+
+               /* Copy the final "$" */
                *dst++ = *src++;
                size--;
        }