trace: avoid unnecessary quoting

Trace output which contains arbitrary strings (e.g., the
arguments to commands which we are running) is always passed
through sq_quote_buf(). That function always adds
single-quotes, even if the output consists of vanilla
characters. This can make the output a bit hard to read.

Let's avoid the quoting if there are no characters which a
shell would interpret. Trace output doesn't necessarily need
to be shell-compatible, but:

  - the shell language is a good ballpark for what humans
    consider readable (well, humans versed in command line
    tools)

  - the run_command bits can be cut-and-pasted to a shell,
    and we'll keep that property

  - it covers any cases which would make the output
    visually ambiguous (e.g., embedded whitespace or quotes)

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

quote.c

@@ -43,6 +43,22 @@ void sq_quote_buf(struct strbuf *dst, const char *src)
 	free(to_free);
 }
 
+void sq_quote_buf_pretty(struct strbuf *dst, const char *src)
+{
+	static const char ok_punct[] = "+,-./:=@_^";
+	const char *p;
+
+	for (p = src; *p; p++) {
+		if (!isalpha(*p) && !isdigit(*p) && !strchr(ok_punct, *p)) {
+			sq_quote_buf(dst, src);
+			return;
+		}
+	}
+
+	/* if we get here, we did not need quoting */
+	strbuf_addstr(dst, src);
+}
+
 void sq_quotef(struct strbuf *dst, const char *fmt, ...)
 {
 	struct strbuf src = STRBUF_INIT;
@@ -68,6 +84,16 @@ void sq_quote_argv(struct strbuf *dst, const char **argv)
 	}
 }
 
+void sq_quote_argv_pretty(struct strbuf *dst, const char **argv)
+{
+	int i;
+
+	for (i = 0; argv[i]; i++) {
+		strbuf_addch(dst, ' ');
+		sq_quote_buf_pretty(dst, argv[i]);
+	}
+}
+
 static char *sq_dequote_step(char *arg, char **next)
 {
 	char *dst = arg;

quote.h

@@ -33,6 +33,14 @@ extern void sq_quote_buf(struct strbuf *, const char *src);
 extern void sq_quote_argv(struct strbuf *, const char **argv);
 extern void sq_quotef(struct strbuf *, const char *fmt, ...);
 
+/*
+ * These match their non-pretty variants, except that they avoid
+ * quoting when there are no exotic characters. These should only be used for
+ * human-readable output, as sq_dequote() is not smart enough to dequote it.
+ */
+void sq_quote_buf_pretty(struct strbuf *, const char *src);
+void sq_quote_argv_pretty(struct strbuf *, const char **argv);
+
 /* This unwraps what sq_quote() produces in place, but returns
  * NULL if the input does not look like what sq_quote would have
  * produced.

trace.c

@@ -157,7 +157,7 @@ static void trace_argv_vprintf_fl(const char *file, int line,
 
 	strbuf_vaddf(&buf, format, ap);
 
-	sq_quote_argv(&buf, argv);
+	sq_quote_argv_pretty(&buf, argv);
 	print_trace_line(&trace_default_key, &buf);
 }
 
@@ -426,6 +426,6 @@ void trace_command_performance(const char **argv)
 		atexit(print_command_performance_atexit);
 
 	strbuf_reset(&command_line);
-	sq_quote_argv(&command_line, argv);
+	sq_quote_argv_pretty(&command_line, argv);
 	command_start_time = getnanotime();
 }