"log --author=me --grep=it" should find intersection, not union

Historically, any grep filter in "git log" family of commands were taken
as restricting to commits with any of the words in the commit log message.
However, the user almost always want to find commits "done by this person
on that topic".  With "--all-match" option, a series of grep patterns can
be turned into a requirement that all of them must produce a match, but
that makes it impossible to ask for "done by me, on either this or that"
with:

	log --author=me --committer=him --grep=this --grep=that

because it will require both "this" and "that" to appear.

Change the "header" parser of grep library to treat the headers specially,
and parse it as:

	(all-match-OR (HEADER-AUTHOR me)
		      (HEADER-COMMITTER him)
		      (OR
		      	(PATTERN this)
			(PATTERN that) ) )

Even though the "log" command line parser doesn't give direct access to
the extended grep syntax to group terms with parentheses, this change will
cover the majority of the case the users would want.

This incidentally revealed that one test in t7002 was bogus.  It ran:

	log --author=Thor --grep=Thu --format='%s'

and expected (wrongly) "Thu" to match "Thursday" in the author/committer
date, but that would never match, as the timestamp in raw commit buffer
does not have the name of the day-of-the-week.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 40 insertions, 6 deletions

diff --git a/grep.c b/grep.c
index bdadf2c0cc..eee99f31f1 100644
--- a/grep.c
+++ b/grep.c
@@ -11,8 +11,8 @@ void append_header_grep_pattern(struct grep_opt *opt, enum grep_header_field fie
 	p->no = 0;
 	p->token = GREP_PATTERN_HEAD;
 	p->field = field;
-	*opt->pattern_tail = p;
-	opt->pattern_tail = &p->next;
+	*opt->header_tail = p;
+	opt->header_tail = &p->next;
 	p->next = NULL;
 }
 
@@ -172,9 +172,26 @@ static struct grep_expr *compile_pattern_expr(struct grep_pat **list)
 void compile_grep_patterns(struct grep_opt *opt)
 {
 	struct grep_pat *p;
-
-	if (opt->all_match)
-		opt->extended = 1;
+	struct grep_expr *header_expr = NULL;
+
+	if (opt->header_list) {
+		p = opt->header_list;
+		header_expr = compile_pattern_expr(&p);
+		if (p)
+			die("incomplete pattern expression: %s", p->pattern);
+		for (p = opt->header_list; p; p = p->next) {
+			switch (p->token) {
+			case GREP_PATTERN: /* atom */
+			case GREP_PATTERN_HEAD:
+			case GREP_PATTERN_BODY:
+				compile_regexp(p, opt);
+				break;
+			default:
+				opt->extended = 1;
+				break;
+			}
+		}
+	}
 
 	for (p = opt->pattern_list; p; p = p->next) {
 		switch (p->token) {
@@ -189,7 +206,9 @@ void compile_grep_patterns(struct grep_opt *opt)
 		}
 	}
 
-	if (!opt->extended)
+	if (opt->all_match || header_expr)
+		opt->extended = 1;
+	else if (!opt->extended)
 		return;
 
 	/* Then bundle them up in an expression.
@@ -200,6 +219,21 @@ void compile_grep_patterns(struct grep_opt *opt)
 		opt->pattern_expression = compile_pattern_expr(&p);
 	if (p)
 		die("incomplete pattern expression: %s", p->pattern);
+
+	if (!header_expr)
+		return;
+
+	if (opt->pattern_expression) {
+		struct grep_expr *z;
+		z = xcalloc(1, sizeof(*z));
+		z->node = GREP_NODE_OR;
+		z->u.binary.left = opt->pattern_expression;
+		z->u.binary.right = header_expr;
+		opt->pattern_expression = z;
+	} else {
+		opt->pattern_expression = header_expr;
+	}
+	opt->all_match = 1;
 }
 
 static void free_pattern_expr(struct grep_expr *x)