Merge branch 'tb/macos-iconv-workarounds' into jch

The iconv library on macOS fails to correctly handle stateful
ISO/IEC 2022 encoded strings.  Work it around instead of replacing
it wholesale from homebrew.

RFC.
needs to be debased from older rs/macos-iconv-workaround topic.

* tb/macos-iconv-workarounds:
  utf8.c: Enable workaround for iconv under macOS 14/15
  utf8.c: Prepare workaround for iconv under macOS 14/15

Makefile

@@ -1693,6 +1693,7 @@ ifeq ($(uname_S),Darwin)
                 ifeq ($(shell test -d /opt/local/lib && echo y),y)
 			BASIC_CFLAGS += -I/opt/local/include
 			BASIC_LDFLAGS += -L/opt/local/lib
+			HAS_GOOD_LIBICONV = Yes
                 endif
         endif
         ifndef NO_APPLE_COMMON_CRYPTO
@@ -1715,6 +1716,7 @@ endif
 ifdef USE_HOMEBREW_LIBICONV
 ifeq ($(shell test -d $(HOMEBREW_PREFIX)/opt/libiconv && echo y),y)
 	ICONVDIR ?= $(HOMEBREW_PREFIX)/opt/libiconv
+	HAS_GOOD_LIBICONV = Yes
 endif
 endif
 endif
@@ -1860,6 +1862,11 @@ ifndef NO_ICONV
                 endif
 		EXTLIBS += $(ICONV_LINK) -liconv
         endif
+        ifdef NEEDS_GOOD_LIBICONV
+        ifndef HAS_GOOD_LIBICONV
+                BASIC_CFLAGS += -DICONV_RESTART_RESET
+        endif
+        endif
 endif
 ifdef ICONV_OMITS_BOM
 	BASIC_CFLAGS += -DICONV_OMITS_BOM

config.mak.uname

@@ -157,6 +157,7 @@ ifeq ($(uname_S),Darwin)
         endif
         ifeq ($(shell test "$(DARWIN_MAJOR_VERSION)" -ge 24 && echo 1),1)
 		USE_HOMEBREW_LIBICONV = UnfortunatelyYes
+		NEEDS_GOOD_LIBICONV = UnfortunatelyYes
         endif
 
 	# The builtin FSMonitor on MacOS builds upon Simple-IPC.  Both require

utf8.c

@@ -515,6 +515,19 @@ char *reencode_string_iconv(const char *in, size_t insz, iconv_t conv,
 			out = xrealloc(out, outalloc);
 			outpos = out + sofar;
 			outsz = outalloc - sofar - 1;
+#ifdef ICONV_RESTART_RESET
+			/*
+			 * If iconv(3) messes up piecemeal conversions
+			 * then restore the original pointers, sizes,
+			 * and converter state, then retry converting
+			 * the full string using the reallocated buffer.
+			 */
+			insz += cp - (iconv_ibp)in; /* Restore insz */
+			cp = (iconv_ibp)in;         /* original start value */
+			outpos = out + bom_len;     /* original start value */
+			outsz = outalloc - bom_len - 1; /* new len */
+			iconv(conv, NULL, NULL, NULL, NULL); /* reset iconv machinery */
+#endif
 		}
 		else {
 			*outpos = '\0';