Don't just accept git-forbidden tags

[eyalroz]

Some tags which are acceptable in CVS, are unacceptable in git. See this StackOverflow answer for a list of disallowed character sequences in tag names.

crap doesn't check tag names against these restrictions, and just goes ahead and accepts them into the tag database in read_file_versions(). Now, when it later encounters such a tag in going over the commit / tagging history, something fails/crashes (perhaps cvs-fast-export? git-fast-import?) and the process is terminated.

I'm not exactly sure what the solution should be, since I'm having trouble following to code to realize exactly where the tag name is used later on.

A (poor) workaround which I've somehow managed to hack together is simply not inserting problematic tag into the tag DB within read_file_versions(); but it's not the right thing to do. What is the right thing to do?

Option 1:

• Keep the tag in the tag DB, but mark it as git-unacceptable
• Whenever we see the tag used/applied, emit a warning message, and skip its use.

Option 2:

• Keep the tag in the tag DB, but "escape" it somehow, e.g. badtag/ becomes crap_escaped_badtag_slash. (Perhaps it's a good idea to ensure that no such tag already exists in the repository)
• Whenever we see the tag used/applied, apply instead the escaped tag.

Option 3:

Support both options 1 and 2, and let a command-line switch choose between them. Default to escaping rather than deleting, I would say.

[eyalroz]

I'm not offering a PR this time (probably), but here is a bit of code:

bool tag_name_is_valid(const char* restrict str, size_t len)
{
	// Rules as appear here:
	// https://stackoverflow.com/a/26382358/1593077

	// rule 1
	if (str[0] == '.') { return false; }
	if (strstr(str, "/.")) { return false; }
	if (strstr(str, ".lock/")) { return false; }
	if (strcmp(str + len - 5, ".lock") == 0) { return false; }
	// rule 2 - unused, since theoretically we could have "allow-onelevel"
	// if (strchr(str, '/') == NULL) { return false; }
	// rule 3
	if (strstr(str, "..")) { return false; }
	// rule 4
	for(size_t i; i < len; i++) {
		char c = str[i];
		bool is_ascii_control_char = (c < 0x20) || (c == 0x7F /* DEL */);
		if (is_ascii_control_char || c == ' ' || c == '~' || c == '^' || c ==':' ) return false;
	}
	// rule 4
	if ( (strpbrk(str, "?*[") != NULL) ) { return false; }
	// rule 5
	if ( (strpbrk(str, "?*[") != NULL) ) { return false; }
	// rule 6
	if ( (str[0]) || (str[len - 1] == '/') || (strstr(str, "//") != NULL) ) { return false; }
	// rule 7
	if (str[len - 1] == '.') { return false; }
	// rule 8
	if (strchr(str,"@{") != NULL) { return false; }
	// rule 9
	if (str[0] == '@' && len == 1) { return false; }
	// rule 10
	if (strchr(str, '\\') != NULL) { return false; }
	return true;
}