[PATCH/RFC v1 1/1] convert.c: Escape sequences only for a tty in trace_encoding()

[tboegi@web.de]

From: Torsten Bögershausen <tboegi@web.de>

The content of a buffer can be dumped using trace_encoding()
before and after the encoding is converted.
The current function trace_encoding() in convert.c tries to
make the output easier to read:
The byte position and the character itself are dimmed, allowing
the eye to focus on the hex values in the byte stream.

ANSI escape sequences are used to "dim" the display temporally,
and to restore the normal brightness.

When stdout is re-directed into a file, those sequences are not
working as expected (but shown in the editor) which is disturbing.
rather then helpful.

Disable them, if stdout is not a tty.

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
---
 I am temped to remove the "dim" functionality all together,
 or to remove the printout of the values which are now dimmed,
 what do others think ?

convert.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/convert.c b/convert.c
index 5d0307fc10..70e58f1413 100644
--- a/convert.c
+++ b/convert.c
@@ -42,6 +42,9 @@ struct text_stat {
 	unsigned printable, nonprintable;
 };

+static const char *terminal_half_bright;
+static const char *terminal_reset_normal;
+
 static void gather_stats(const char *buf, unsigned long size, struct text_stat *stats)
 {
 	unsigned long i;
@@ -330,14 +333,23 @@ static void trace_encoding(const char *context, const char *path,
 	static struct trace_key coe = TRACE_KEY_INIT(WORKING_TREE_ENCODING);
 	struct strbuf trace = STRBUF_INIT;
 	int i;
-
+	if (!terminal_half_bright || !terminal_reset_normal) {
+		if (isatty(1)) {
+			terminal_half_bright  = "\033[2m";
+			terminal_reset_normal = "\033[0m";
+		} else {
+			terminal_half_bright = "";
+			terminal_reset_normal = "";
+		}
+	}
 	strbuf_addf(&trace, "%s (%s, considered %s):\n", context, path, encoding);
 	for (i = 0; i < len && buf; ++i) {
+		char c = buf[i] > 32 && buf[i] < 127 ? buf[i] : ' ';
 		strbuf_addf(
-			&trace, "| \033[2m%2i:\033[0m %2x \033[2m%c\033[0m%c",
-			i,
+			&trace, "| %s%2i:%s %2x %s%c%s%c",
+			terminal_half_bright, i, terminal_reset_normal,
 			(unsigned char) buf[i],
-			(buf[i] > 32 && buf[i] < 127 ? buf[i] : ' '),
+			terminal_half_bright, c, terminal_reset_normal,
 			((i+1) % 8 && (i+1) < len ? ' ' : '\n')
 		);
 	}
--
2.21.0.135.g6e0cc67761