utf8.c: print warning about disabled iconvmk/utf8-no-iconv-warn

It is an allowed compile-time option to build git without iconv
support. Resulting build almost always functions correctly, and
never displays that it is missing anything, but reencode_string_len()
just never modifies its input. This gives undesirable result that
returned data or even data written into repository is incorrect
and user is not aware about it.

Show warning there is non-trivial reencoding requested. Show it only once
during program run.

Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 15 insertions, 3 deletions

diff --git a/utf8.c b/utf8.c
index 28e6d76a42..85fa2cd03f 100644
--- a/utf8.c
+++ b/utf8.c
@@ -521,6 +521,19 @@ char *reencode_string_len(const char *in, int insz,
 	iconv_close(conv);
 	return out;
 }
+#else
+static int noiconv_warning_shown = 0;
+
+char *reencode_string_len(const char *in, int insz,
+			  const char *out_encoding, const char *in_encoding,
+			  int *outsz)
+{
+	if (!same_encoding(in_encoding, out_encoding) && !noiconv_warning_shown) {
+		warning("Iconv support is disabled at compile time. It is likely that\nincorrect data will be printed or stored in repository.\nConsider using other build for this task.");
+		noiconv_warning_shown = 1;
+	}
+	return NULL;
+}
 #endif
 
 /*
diff --git a/utf8.h b/utf8.h
index e7b2aa4168..c72998b152 100644
--- a/utf8.h
+++ b/utf8.h
@@ -26,13 +26,12 @@ void strbuf_utf8_replace(struct strbuf *sb, int pos, int width,
 #ifndef NO_ICONV
 char *reencode_string_iconv(const char *in, size_t insz,
 			    iconv_t conv, int *outsz);
+#endif
+
 char *reencode_string_len(const char *in, int insz,
 			  const char *out_encoding,
 			  const char *in_encoding,
 			  int *outsz);
-#else
-#define reencode_string_len(a,b,c,d,e) NULL
-#endif
 
 static inline char *reencode_string(const char *in,
 				    const char *out_encoding,