sideband: highlight keywords in remote sideband output

The colorization is controlled with the config setting "color.remote".

Supported keywords are "error", "warning", "hint" and "success". They
are highlighted if they appear at the start of the line, which is
common in error messages, eg.

   ERROR: commit is missing Change-Id

The Git push process itself prints lots of non-actionable messages
(eg. bandwidth statistics, object counters for different phases of the
process). This obscures actionable error messages that servers may
send back. Highlighting keywords in the sideband draws more attention
to those messages.

The background for this change is that Gerrit does server-side
processing to create or update code reviews, and actionable error
messages (eg. missing Change-Id) must be communicated back to the user
during the push. User research has shown that new users have trouble
seeing these messages.

The highlighting is done on the client rather than server side, so
servers don't have to grow capabilities to understand terminal escape
codes and terminal state. It also consistent with the current state
where Git is control of the local display (eg. prefixing messages with
"remote: ").

The highlighting can be configured using color.remote.<KEYWORD>
configuration settings. Since the keys are matched case insensitively,
we match the keywords case insensitively too.

Finally, this solution is backwards compatible: many servers already
prefix their messages with "error", and they will benefit from this
change without requiring a server update. By contrast, a server-side
solution would likely require plumbing the TERM variable through the
git protocol, so it would require changes to both server and client.

Helped-by: Duy Nguyen <pclouds@gmail.com>
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

5 files changed, 217 insertions, 9 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 63365dcf3d..9a38dd2cbb 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1263,6 +1263,18 @@ color.push::
 color.push.error::
 	Use customized color for push errors.
 
+color.remote::
+	If set, keywords at the start of the line are highlighted. The
+	keywords are "error", "warning", "hint" and "success", and are
+	matched case-insensitively. May be set to `always`, `false` (or
+	`never`) or `auto` (or `true`). If unset, then the value of
+	`color.ui` is used (`auto` by default).
+
+color.remote.<slot>::
+	Use customized color for each remote keyword. `<slot>` may be
+	`hint`, `warning`, `success` or `error` which match the
+	corresponding keyword.
+
 color.showBranch::
 	A boolean to enable/disable color in the output of
 	linkgit:git-show-branch[1]. May be set to `always`,
diff --git a/help.c b/help.c
index 3ebf0568db..b6cafcfc0a 100644
--- a/help.c
+++ b/help.c
@@ -425,6 +425,7 @@ void list_config_help(int for_human)
 		{ "color.diff", "<slot>", list_config_color_diff_slots },
 		{ "color.grep", "<slot>", list_config_color_grep_slots },
 		{ "color.interactive", "<slot>", list_config_color_interactive_slots },
+		{ "color.remote", "<slot>", list_config_color_sideband_slots },
 		{ "color.status", "<slot>", list_config_color_status_slots },
 		{ "fsck", "<msg-id>", list_config_fsck_msg_ids },
 		{ "receive.fsck", "<msg-id>", list_config_fsck_msg_ids },
diff --git a/help.h b/help.h
index f8b15323a6..9eab6a3f89 100644
--- a/help.h
+++ b/help.h
@@ -83,6 +83,7 @@ void list_config_color_diff_slots(struct string_list *list, const char *prefix);
 void list_config_color_grep_slots(struct string_list *list, const char *prefix);
 void list_config_color_interactive_slots(struct string_list *list, const char *prefix);
 void list_config_color_status_slots(struct string_list *list, const char *prefix);
+void list_config_color_sideband_slots(struct string_list *list, const char *prefix);
 void list_config_fsck_msg_ids(struct string_list *list, const char *prefix);
 
 #endif /* HELP_H */
diff --git a/sideband.c b/sideband.c
index 325bf0e974..1c6bb0e25b 100644
--- a/sideband.c
+++ b/sideband.c
@@ -1,6 +1,109 @@
 #include "cache.h"
+#include "color.h"
+#include "config.h"
 #include "pkt-line.h"
 #include "sideband.h"
+#include "help.h"
+
+struct keyword_entry {
+	/*
+	 * We use keyword as config key so it should be a single alphanumeric word.
+	 */
+	const char *keyword;
+	char color[COLOR_MAXLEN];
+};
+
+static struct keyword_entry keywords[] = {
+	{ "hint",	GIT_COLOR_YELLOW },
+	{ "warning",	GIT_COLOR_BOLD_YELLOW },
+	{ "success",	GIT_COLOR_BOLD_GREEN },
+	{ "error",	GIT_COLOR_BOLD_RED },
+};
+
+/* Returns a color setting (GIT_COLOR_NEVER, etc). */
+static int use_sideband_colors(void)
+{
+	static int use_sideband_colors_cached = -1;
+
+	const char *key = "color.remote";
+	struct strbuf sb = STRBUF_INIT;
+	char *value;
+	int i;
+
+	if (use_sideband_colors_cached >= 0)
+		return use_sideband_colors_cached;
+
+	if (!git_config_get_string(key, &value)) {
+		use_sideband_colors_cached = git_config_colorbool(key, value);
+	} else if (!git_config_get_string("color.ui", &value)) {
+		use_sideband_colors_cached = git_config_colorbool("color.ui", value);
+	} else {
+		use_sideband_colors_cached = GIT_COLOR_AUTO;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(keywords); i++) {
+		strbuf_reset(&sb);
+		strbuf_addf(&sb, "%s.%s", key, keywords[i].keyword);
+		if (git_config_get_string(sb.buf, &value))
+			continue;
+		if (color_parse(value, keywords[i].color))
+			continue;
+	}
+	strbuf_release(&sb);
+	return use_sideband_colors_cached;
+}
+
+void list_config_color_sideband_slots(struct string_list *list, const char *prefix)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(keywords); i++)
+		list_config_item(list, prefix, keywords[i].keyword);
+}
+
+/*
+ * Optionally highlight one keyword in remote output if it appears at the start
+ * of the line. This should be called for a single line only, which is
+ * passed as the first N characters of the SRC array.
+ */
+static void maybe_colorize_sideband(struct strbuf *dest, const char *src, int n)
+{
+	int i;
+
+	if (!want_color_stderr(use_sideband_colors())) {
+		strbuf_add(dest, src, n);
+		return;
+	}
+
+	while (isspace(*src)) {
+		strbuf_addch(dest, *src);
+		src++;
+		n--;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(keywords); i++) {
+		struct keyword_entry *p = keywords + i;
+		int len = strlen(p->keyword);
+		/*
+		 * Match case insensitively, so we colorize output from existing
+		 * servers regardless of the case that they use for their
+		 * messages. We only highlight the word precisely, so
+		 * "successful" stays uncolored.
+		 */
+		if (!strncasecmp(p->keyword, src, len) && !isalnum(src[len])) {
+			strbuf_addstr(dest, p->color);
+			strbuf_add(dest, src, len);
+			strbuf_addstr(dest, GIT_COLOR_RESET);
+			n -= len;
+			src += len;
+			break;
+		}
+	}
+
+	strbuf_add(dest, src, n);
+
+}
+
 
 /*
  * Receive multiplexed output stream over git native protocol.
@@ -48,8 +151,10 @@ int recv_sideband(const char *me, int in_stream, int out)
 		len--;
 		switch (band) {
 		case 3:
-			strbuf_addf(&outbuf, "%s%s%s", outbuf.len ? "\n" : "",
-				    DISPLAY_PREFIX, buf + 1);
+			strbuf_addf(&outbuf, "%s%s", outbuf.len ? "\n" : "",
+				    DISPLAY_PREFIX);
+			maybe_colorize_sideband(&outbuf, buf + 1, len);
+
 			retval = SIDEBAND_REMOTE_ERROR;
 			break;
 		case 2:
@@ -69,20 +174,22 @@ int recv_sideband(const char *me, int in_stream, int out)
 				if (!outbuf.len)
 					strbuf_addstr(&outbuf, DISPLAY_PREFIX);
 				if (linelen > 0) {
-					strbuf_addf(&outbuf, "%.*s%s%c",
-						    linelen, b, suffix, *brk);
-				} else {
-					strbuf_addch(&outbuf, *brk);
+					maybe_colorize_sideband(&outbuf, b, linelen);
+					strbuf_addstr(&outbuf, suffix);
 				}
+
+				strbuf_addch(&outbuf, *brk);
 				xwrite(2, outbuf.buf, outbuf.len);
 				strbuf_reset(&outbuf);
 
 				b = brk + 1;
 			}
 
-			if (*b)
-				strbuf_addf(&outbuf, "%s%s", outbuf.len ?
-					    "" : DISPLAY_PREFIX, b);
+			if (*b) {
+				strbuf_addstr(&outbuf, outbuf.len ?
+					    "" : DISPLAY_PREFIX);
+				maybe_colorize_sideband(&outbuf, b, strlen(b));
+			}
 			break;
 		case 1:
 			write_or_die(out, buf + 1, len);
diff --git a/t/t5409-colorize-remote-messages.sh b/t/t5409-colorize-remote-messages.sh
new file mode 100755
index 0000000000..eb1b8aa05d
--- /dev/null
+++ b/t/t5409-colorize-remote-messages.sh
@@ -0,0 +1,87 @@
+#!/bin/sh
+
+test_description='remote messages are colorized on the client'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	mkdir .git/hooks &&
+	write_script .git/hooks/update <<-\EOF &&
+	echo error: error
+	echo ERROR: also highlighted
+	echo hint: hint
+	echo hinting: not highlighted
+	echo success: success
+	echo warning: warning
+	echo prefixerror: error
+	echo " " "error: leading space"
+	exit 0
+	EOF
+	echo 1 >file &&
+	git add file &&
+	git commit -m 1 &&
+	git clone . child &&
+	(
+		cd child &&
+		test_commit message2 file content2
+	)
+'
+
+test_expect_success 'keywords' '
+	git --git-dir child/.git -c color.remote=always push -f origin HEAD:refs/heads/keywords 2>output &&
+	test_decode_color <output >decoded &&
+	grep "<BOLD;RED>error<RESET>: error" decoded &&
+	grep "<YELLOW>hint<RESET>:" decoded &&
+	grep "<BOLD;GREEN>success<RESET>:" decoded &&
+	grep "<BOLD;YELLOW>warning<RESET>:" decoded
+'
+
+test_expect_success 'whole words at line start' '
+	git --git-dir child/.git -c color.remote=always push -f origin HEAD:refs/heads/whole-words 2>output &&
+	test_decode_color <output >decoded &&
+	grep "<YELLOW>hint<RESET>:" decoded &&
+	grep "hinting: not highlighted" decoded &&
+	grep "prefixerror: error" decoded
+'
+
+test_expect_success 'case-insensitive' '
+	git --git-dir child/.git -c color.remote=always push -f origin HEAD:refs/heads/case-insensitive 2>output &&
+	cat output &&
+	test_decode_color <output >decoded &&
+	grep "<BOLD;RED>error<RESET>: error" decoded &&
+	grep "<BOLD;RED>ERROR<RESET>: also highlighted" decoded
+'
+
+test_expect_success 'leading space' '
+	git --git-dir child/.git -c color.remote=always push -f origin HEAD:refs/heads/leading-space 2>output &&        cat output &&
+	test_decode_color <output >decoded &&
+	grep "  <BOLD;RED>error<RESET>: leading space" decoded
+'
+
+test_expect_success 'no coloring for redirected output' '
+	git --git-dir child/.git push -f origin HEAD:refs/heads/redirected-output 2>output &&
+	test_decode_color <output >decoded &&
+	grep "error: error" decoded
+'
+
+test_expect_success 'push with customized color' '
+	git --git-dir child/.git -c color.remote=always -c color.remote.error=blue push -f origin HEAD:refs/heads/customized-color 2>output &&
+	test_decode_color <output >decoded &&
+	grep "<BLUE>error<RESET>:" decoded &&
+	grep "<BOLD;GREEN>success<RESET>:" decoded
+'
+
+
+test_expect_success 'error in customized color' '
+	git --git-dir child/.git -c color.remote=always -c color.remote.error=i-am-not-a-color push -f origin HEAD:refs/heads/error-customized-color 2>output &&
+	test_decode_color <output >decoded &&
+	grep "<BOLD;GREEN>success<RESET>:" decoded
+'
+
+test_expect_success 'fallback to color.ui' '
+	git --git-dir child/.git -c color.ui=always push -f origin HEAD:refs/heads/fallback-color-ui 2>output &&
+	test_decode_color <output >decoded &&
+	grep "<BOLD;RED>error<RESET>: error" decoded
+'
+
+test_done