convert: add tracing for checkout-encoding

Add the GIT_TRACE_CHECKOUT_ENCODING environment variable to enable
tracing for content that is reencoded with the checkout-encoding
attribute.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>

convert.c

@@ -257,6 +257,29 @@ static int will_convert_lf_to_crlf(size_t len, struct text_stat *stats,
 
 }
 
+static void trace_encoding(const char *context, const char *path,
+			   const char *encoding, const char *buf, size_t len)
+{
+	static struct trace_key coe = TRACE_KEY_INIT(CHECKOUT_ENCODING);
+	struct strbuf trace = STRBUF_INIT;
+	int i;
+
+	strbuf_addf(&trace, "%s (%s, considered %s):\n", context, path, encoding);
+	for (i = 0; i < len && buf; ++i) {
+		strbuf_addf(
+			&trace,"| \e[2m%2i:\e[0m %2x \e[2m%c\e[0m%c",
+			i,
+			(unsigned char) buf[i],
+			(buf[i] > 32 && buf[i] < 127 ? buf[i] : ' '),
+			((i+1) % 8 && (i+1) < len ? ' ' : '\n')
+		);
+	}
+	strbuf_addchars(&trace, '\n', 1);
+
+	trace_strbuf(&coe, &trace);
+	strbuf_release(&trace);
+}
+
 static struct encoding {
 	const char *name;
 	struct encoding *next;
@@ -316,6 +339,7 @@ static int encode_to_git(const char *path, const char *src, size_t src_len,
 			error(error_msg, path, enc->name);
 	}
 
+	trace_encoding("source", path, enc->name, src, src_len);
 	dst = reencode_string_len(src, src_len, default_encoding, enc->name,
 				  &dst_len);
 	if (!dst) {
@@ -331,6 +355,7 @@ static int encode_to_git(const char *path, const char *src, size_t src_len,
 		else
 			error(msg, path, enc->name, default_encoding);
 	}
+	trace_encoding("destination", path, default_encoding, dst, dst_len);
 
 	/*
 	 * UTF supports lossless round tripping [1]. UTF to other encoding are
@@ -356,6 +381,9 @@ static int encode_to_git(const char *path, const char *src, size_t src_len,
 					     enc->name, default_encoding,
 					     &re_src_len);
 
+		trace_encoding("reencoded source", path, enc->name,
+			       re_src, re_src_len);
+
 		if (!re_src || src_len != re_src_len ||
 		    memcmp(src, re_src, src_len)) {
 			const char* msg = _("encoding '%s' from %s to %s and "

t/t0028-checkout-encoding.sh

@@ -4,6 +4,8 @@ test_description='checkout-encoding conversion via gitattributes'
 
 . ./test-lib.sh
 
+GIT_TRACE_CHECKOUT_ENCODING=1 && export GIT_TRACE_CHECKOUT_ENCODING
+
 test_expect_success 'setup test repo' '
 
 	text="hallo there!\ncan you read me?" &&