[PATCH] Teach for-each-ref about a little language called Tcl.

Love it or hate it, some people actually still program in Tcl.  Some
of those programs are meant for interfacing with Git.  Programs such as
gitk and git-gui.  It may be useful to have Tcl-safe output available
from for-each-ref, just like shell, Perl and Python already enjoy.

Signed-off-by: Shawn O. Pearce <redacted>
---
 Documentation/git-for-each-ref.txt |    4 ++--
 builtin-for-each-ref.c             |   10 ++++++++++
 quote.c                            |   16 ++++++++++++++++
 quote.h                            |    1 +
 4 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt
index 06e7ab1..da52eba 100644
--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt

@@ -7,7 +7,7 @@ git-for-each-ref - Output information on each ref
 
 SYNOPSIS
 --------
-'git-for-each-ref' [--count=<count>]\* [--shell|--perl|--python] [--sort=<key>]\* [--format=<format>] [<pattern>]
+'git-for-each-ref' [--count=<count>]\* [--shell|--perl|--python|--tcl] [--sort=<key>]\* [--format=<format>] [<pattern>]
 
 DESCRIPTION
 -----------

@@ -49,7 +49,7 @@ OPTIONS
 	using fnmatch(3).  Refs that do not match the pattern
 	are not shown.
 
---shell, --perl, --python::
+--shell, --perl, --python, --tcl::
 	If given, strings that substitute `%(fieldname)`
 	placeholders are quoted as string literals suitable for
 	the specified host language.  This is meant to produce

diff --git a/builtin-for-each-ref.c b/builtin-for-each-ref.c
index af72a12..9d5f266 100644
--- a/builtin-for-each-ref.c
+++ b/builtin-for-each-ref.c

@@ -12,6 +12,7 @@
 #define QUOTE_SHELL 1
 #define QUOTE_PERL 2
 #define QUOTE_PYTHON 3
+#define QUOTE_TCL 4
 
 typedef enum { FIELD_STR, FIELD_ULONG, FIELD_TIME } cmp_type;
 

@@ -723,6 +724,9 @@ static void print_value(struct refinfo *ref, int atom, int quote_style)
 	case QUOTE_PYTHON:
 		python_quote_print(stdout, v->s);
 		break;
+	case QUOTE_TCL:
+		tcl_quote_print(stdout, v->s);
+		break;
 	}
 }
 

@@ -834,6 +838,12 @@ int cmd_for_each_ref(int ac, const char **av, char *prefix)
 			quote_style = QUOTE_PYTHON;
 			continue;
 		}
+		if (!strcmp(arg, "--tcl") ) {
+			if (0 <= quote_style)
+				die("more than one quoting style?");
+			quote_style = QUOTE_TCL;
+			continue;
+		}
 		if (!strncmp(arg, "--count=", 8)) {
 			if (maxcount)
 				die("more than one --count?");

diff --git a/quote.c b/quote.c
index a418a0f..ab0e971 100644
--- a/quote.c
+++ b/quote.c

@@ -387,3 +387,19 @@ void python_quote_print(FILE *stream, const char *src)
 	}
 	fputc(sq, stream);
 }
+
+void tcl_quote_print(FILE *stream, const char *src)
+{
+	const char lb = '{';
+	const char rb = '}';
+	const char bq = '\\';
+	char c;
+
+	fputc(lb, stream);
+	while ((c = *src++)) {
+		if (c == lb || c == rb || c == bq)
+			fputc(bq, stream);
+		fputc(c, stream);
+	}
+	fputc(rb, stream);
+}

diff --git a/quote.h b/quote.h
index b55e699..bdc3610 100644
--- a/quote.h
+++ b/quote.h

@@ -55,5 +55,6 @@ extern void write_name_quoted(const char *prefix, int prefix_len,
 /* quoting as a string literal for other languages */
 extern void perl_quote_print(FILE *stream, const char *src);
 extern void python_quote_print(FILE *stream, const char *src);
+extern void tcl_quote_print(FILE *stream, const char *src);
 
 #endif

-- 
1.5.0.rc2.g8a816

On Sat, 27 Jan 2007 02:22:58 -0500 Shawn O. Pearce wrote:

Love it or hate it, some people actually still program in Tcl.  Some
of those programs are meant for interfacing with Git.  Programs such as
gitk and git-gui.  It may be useful to have Tcl-safe output available
from for-each-ref, just like shell, Perl and Python already enjoy.

[...]

+void tcl_quote_print(FILE *stream, const char *src)
+{
+	const char lb = '{';
+	const char rb = '}';
+	const char bq = '\\';
+	char c;
+
+	fputc(lb, stream);
+	while ((c = *src++)) {
+		if (c == lb || c == rb || c == bq)
+			fputc(bq, stream);
+		fputc(c, stream);
+	}
+	fputc(rb, stream);
+}

No, this is broken - backslashes cannot be used to quote special
characters in braces.

      If  the  first character of a word is an open brace (``{'') then
      the word is terminated by  the  matching  close  brace  (``}'').
      Braces  nest  within  the  word:  for each additional open brace
      there must be an additional close brace  (however,  if  an  open
      brace  or close brace within the word is quoted with a backslash
      then it is not counted in locating the  matching  close  brace).
      No  substitutions  are  performed  on the characters between the
      braces  except  for  backslash-newline  substitutions  described
      below,  nor  do  semi-colons, newlines, close brackets, or white
      space receive any special interpretation.  The word will consist
      of  exactly the characters between the outer braces, not includ-
      ing the braces themselves.

The problem is that using '\{' will protect from nonmatching braces,
but the backslash will stay in the resulting string - it will not be
removed.  Similarly for '\}' and '\\'.

Tcl itself checks whether using braces is safe (it could be safe if
the text does not have nonmatching braces and does not have an odd
number of backslash characters at end of line), and uses just
backslashes if braces cannot be used.  See tclUtil.c,
Tcl_ScanCountedElement() and Tcl_ConvertCountedElement().
This code adds a backslash before ']', '[', '$', ';', ' ', '\\', '"',
'{', '}', and also converts special characters '\f', '\n', '\r', '\t',
'\v' to C-style escape sequences.

Untested code (output will not look very nice, but it is not intended
for human consumption anyway):

void tcl_quote_print(FILE *stream, const char *src)
{
	char c;

	while ((c = *src++)) {
		switch (c) {
		case ']':
		case '[':
		case '$':
		case ';':
		case ' ':
		case '\\':
		case '"':
		case '{':
		case '}':
			fputc('\\', stream);
		default:
			fputc(c, stream);
			break;

		case '\f':
			fputs("\\f", stream);
			break;
		case '\n':
			fputs("\\n", stream);
			break;
		case '\r':
			fputs("\\r", stream);
			break;
		case '\t':
			fputs("\\t", stream);
			break;
		case '\v':
			fputs("\\v", stream);
			break;
		}
	}
}