Re: [PATCH] grep: fix match highlighting for combined patterns with context lines

Zoltan Klinger [off-list ref] writes:

When git grep is run with combined patterns such as '-e p1 --and -e p2'
and surrounding context lines are requested, the output contains
incorrectly highlighted matches.

Consider the following output (highlighted matches are surrounded by '*'
characters):
    $ cat testfile
    foo a
    foo b
    foo bar
    baz bar foo
    bar x
    bar y
    $ git grep -n -C2 -e foo --and -e bar testfile
    testfile-1-*foo* a
    testfile-2-*foo* b
    testfile:3:*foo* *bar*
    testfile:4:baz *bar* *foo*
    testfile-5-*bar* x
    testfile-6-*bar* y

Lines 1, 2, 5 and 6 do not match the combined patterns, they only
contain incorrectly highlighted 'false positives'.

Modify the show_line() function in grep.c to highlight matches only on
lines that match the combined pattern. Do not highlight matches on lines
that provide only context or contain only the function name of the match.

The output of the same command after the change:
    $ git grep -n -C2 -e foo --and -e bar testfile
    testfile-1-foo a
    testfile-2-foo b
    testfile:3:*foo* *bar*
    testfile:4:baz *bar* *foo*
    testfile-5-bar x
    testfile-6-bar y

If your goal is to stop colouring words on context and other kinds
of lines, do you still need the "while (next_match(...))" loop for
them?  Can't you make the resulting code clearer by restructuring
the inside of the whole "if (opt->color)" block further, something
along the lines of...

	if (sign != ':') {
		regmatch_t match; ...
		enum grep_context ctx = GREP_CONTEXT_BODY;
                ...
        	while (next_match(...)) {
                	... the "word-by-word" loop ...
		}
	} else {
        	switch (sign) {
		case '-':
                       	line_color = opt->color_context;
                        break;
		case ':':
                       	line_color = opt->color_function;
                        break;
		}
                output_color(opt, bol, ..., line_color);
	}

Hmm?