Merge branch 'jk/ansi-color'

The output coloring scheme learned two new attributes, italic and
strike, in addition to existing bold, reverse, etc.

* jk/ansi-color:
  color: support strike-through attribute
  color: support "italic" attribute
  color: allow "no-" for negating attributes
  color: refactor parse_attr
  add skip_prefix_mem helper
  doc: refactor description of color format
  color: fix max-size comment

5 files changed, 86 insertions, 39 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e208af118d..db05dec743 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -150,27 +150,34 @@ integer::
        1024", "by 1024x1024", etc.
 
 color::
-       The value for a variables that takes a color is a list of
-       colors (at most two) and attributes (at most one), separated
-       by spaces.  The colors accepted are `normal`, `black`,
-       `red`, `green`, `yellow`, `blue`, `magenta`, `cyan` and
-       `white`; the attributes are `bold`, `dim`, `ul`, `blink` and
-       `reverse`.  The first color given is the foreground; the
-       second is the background.  The position of the attribute, if
-       any, doesn't matter. Attributes may be turned off specifically
-       by prefixing them with `no` (e.g., `noreverse`, `noul`, etc).
-+
-Colors (foreground and background) may also be given as numbers between
-0 and 255; these use ANSI 256-color mode (but note that not all
-terminals may support this).  If your terminal supports it, you may also
-specify 24-bit RGB values as hex, like `#ff0ab3`.
-+
-The attributes are meant to be reset at the beginning of each item
-in the colored output, so setting color.decorate.branch to `black`
-will paint that branch name in a plain `black`, even if the previous
-thing on the same output line (e.g. opening parenthesis before the
-list of branch names in `log --decorate` output) is set to be
-painted with `bold` or some other attribute.
+       The value for a variable that takes a color is a list of
+       colors (at most two, one for foreground and one for background)
+       and attributes (as many as you want), separated by spaces.
++
+The basic colors accepted are `normal`, `black`, `red`, `green`, `yellow`,
+`blue`, `magenta`, `cyan` and `white`.  The first color given is the
+foreground; the second is the background.
++
+Colors may also be given as numbers between 0 and 255; these use ANSI
+256-color mode (but note that not all terminals may support this).  If
+your terminal supports it, you may also specify 24-bit RGB values as
+hex, like `#ff0ab3`.
++
+The accepted attributes are `bold`, `dim`, `ul`, `blink`, `reverse`,
+`italic`, and `strike` (for crossed-out or "strikethrough" letters).
+The position of any attributes with respect to the colors
+(before, after, or in between), doesn't matter. Specific attributes may
+be turned off by prefixing them with `no` or `no-` (e.g., `noreverse`,
+`no-ul`, etc).
++
+For git's pre-defined color slots, the attributes are meant to be reset
+at the beginning of each item in the colored output. So setting
+`color.decorate.branch` to `black` will paint that branch name in a
+plain `black`, even if the previous thing on the same output line (e.g.
+opening parenthesis before the list of branch names in `log --decorate`
+output) is set to be painted with `bold` or some other attribute.
+However, custom log formats may do more complicated and layered
+coloring, and the negated forms may be useful there.
 
 pathname::
 	A variable that takes a pathname value can be given a
diff --git a/color.c b/color.c
index 8f85153d0d..81c2676723 100644
--- a/color.c
+++ b/color.c
@@ -123,19 +123,34 @@ static int parse_color(struct color *out, const char *name, int len)
 	return -1;
 }
 
-static int parse_attr(const char *name, int len)
+static int parse_attr(const char *name, size_t len)
 {
-	static const int attr_values[] = { 1, 2, 4, 5, 7,
-					   22, 22, 24, 25, 27 };
-	static const char * const attr_names[] = {
-		"bold", "dim", "ul", "blink", "reverse",
-		"nobold", "nodim", "noul", "noblink", "noreverse"
+	static const struct {
+		const char *name;
+		size_t len;
+		int val, neg;
+	} attrs[] = {
+#define ATTR(x, val, neg) { (x), sizeof(x)-1, (val), (neg) }
+		ATTR("bold",      1, 22),
+		ATTR("dim",       2, 22),
+		ATTR("italic",    3, 23),
+		ATTR("ul",        4, 24),
+		ATTR("blink",     5, 25),
+		ATTR("reverse",   7, 27),
+		ATTR("strike",    9, 29)
+#undef ATTR
 	};
+	int negate = 0;
 	int i;
-	for (i = 0; i < ARRAY_SIZE(attr_names); i++) {
-		const char *str = attr_names[i];
-		if (!strncasecmp(name, str, len) && !str[len])
-			return attr_values[i];
+
+	if (skip_prefix_mem(name, len, "no", &name, &len)) {
+		skip_prefix_mem(name, len, "-", &name, &len);
+		negate = 1;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(attrs); i++) {
+		if (attrs[i].len == len && !memcmp(attrs[i].name, name, len))
+			return negate ? attrs[i].neg : attrs[i].val;
 	}
 	return -1;
 }
diff --git a/color.h b/color.h
index e155d13f78..6cae166c2b 100644
--- a/color.h
+++ b/color.h
@@ -3,20 +3,23 @@
 
 struct strbuf;
 
-/*  2 + (2 * num_attrs) + 8 + 1 + 8 + 'm' + NUL */
-/* "\033[1;2;4;5;7;38;5;2xx;48;5;2xxm\0" */
 /*
  * The maximum length of ANSI color sequence we would generate:
  * - leading ESC '['            2
- * - attr + ';'                 3 * 10 (e.g. "1;")
+ * - attr + ';'                 2 * num_attr (e.g. "1;")
+ * - no-attr + ';'              3 * num_attr (e.g. "22;")
  * - fg color + ';'             17 (e.g. "38;2;255;255;255;")
  * - bg color + ';'             17 (e.g. "48;2;255;255;255;")
  * - terminating 'm' NUL        2
  *
- * The above overcounts attr (we only use 5 not 8) and one semicolon
- * but it is close enough.
+ * The above overcounts by one semicolon but it is close enough.
+ *
+ * The space for attributes is also slightly overallocated, as
+ * the negation for some attributes is the same (e.g., nobold and nodim).
+ *
+ * We allocate space for 7 attributes.
  */
-#define COLOR_MAXLEN 70
+#define COLOR_MAXLEN 75
 
 /*
  * IMPORTANT: Due to the way these color codes are emulated on Windows,
diff --git a/git-compat-util.h b/git-compat-util.h
index 49d4029b8d..c99cddc54b 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -474,6 +474,23 @@ static inline int skip_prefix(const char *str, const char *prefix,
 }
 
 /*
+ * Like skip_prefix, but promises never to read past "len" bytes of the input
+ * buffer, and returns the remaining number of bytes in "out" via "outlen".
+ */
+static inline int skip_prefix_mem(const char *buf, size_t len,
+				  const char *prefix,
+				  const char **out, size_t *outlen)
+{
+	size_t prefix_len = strlen(prefix);
+	if (prefix_len <= len && !memcmp(buf, prefix, prefix_len)) {
+		*out = buf + prefix_len;
+		*outlen = len - prefix_len;
+		return 1;
+	}
+	return 0;
+}
+
+/*
  * If buf ends with suffix, return 1 and subtract the length of the suffix
  * from *len. Otherwise, return 0 and leave *len untouched.
  */
diff --git a/t/t4026-color.sh b/t/t4026-color.sh
index 2b32c4fbe6..ec78c5e3ac 100755
--- a/t/t4026-color.sh
+++ b/t/t4026-color.sh
@@ -50,14 +50,19 @@ test_expect_success 'attr negation' '
 	color "nobold nodim noul noblink noreverse" "[22;24;25;27m"
 '
 
+test_expect_success '"no-" variant of negation' '
+	color "no-bold no-blink" "[22;25m"
+'
+
 test_expect_success 'long color specification' '
 	color "254 255 bold dim ul blink reverse" "[1;2;4;5;7;38;5;254;48;5;255m"
 '
 
 test_expect_success 'absurdly long color specification' '
 	color \
-	  "#ffffff #ffffff bold nobold dim nodim ul noul blink noblink reverse noreverse" \
-	  "[1;2;4;5;7;22;24;25;27;38;2;255;255;255;48;2;255;255;255m"
+	  "#ffffff #ffffff bold nobold dim nodim italic noitalic
+	   ul noul blink noblink reverse noreverse strike nostrike" \
+	  "[1;2;3;4;5;7;9;22;23;24;25;27;29;38;2;255;255;255;48;2;255;255;255m"
 '
 
 test_expect_success '0-7 are aliases for basic ANSI color names' '