Fix [ed29806baf] by introducing TclUCS4Complete(). All other calls of Tcl_UtfToUniChar() are suspicious, because those cannot handle 4-byte UTF-8 sequences reliable.

So, there's more work to do, but this part can already be backported to Tcl 8.6 and see where we get.

3 files changed, 12 insertions, 9 deletions

diff --git a/generic/tclDecls.h b/generic/tclDecls.h
index 4531be3..c713469 100644
--- a/generic/tclDecls.h
+++ b/generic/tclDecls.h
@@ -4181,7 +4181,7 @@ extern const TclStubs *tclStubsPtr;
 #if defined(USE_TCL_STUBS) && (TCL_UTF_MAX > 3)
 #   undef Tcl_UtfCharComplete
 #   define Tcl_UtfCharComplete(src, length) (((unsigned)((unsigned char)*(src) - 0xF0) < 5) \
-	    ? 4 : tclStubsPtr->tcl_UtfCharComplete((src), (length)))
+	    ? ((length) >= 4) : tclStubsPtr->tcl_UtfCharComplete((src), (length)))
 #endif
 
 #endif /* _TCLDECLS */
diff --git a/generic/tclEncoding.c b/generic/tclEncoding.c
index 4789b7f..422627b 100644
--- a/generic/tclEncoding.c
+++ b/generic/tclEncoding.c
@@ -2300,7 +2300,7 @@ UtfToUtfProc(
     const char *srcStart, *srcEnd, *srcClose;
     const char *dstStart, *dstEnd;
     int result, numChars, charLimit = INT_MAX;
-    Tcl_UniChar *chPtr = (Tcl_UniChar *) statePtr;
+    int *chPtr = (int *) statePtr;
 
     if (flags & TCL_ENCODING_START) {
     	*statePtr = 0;
@@ -2321,7 +2321,7 @@ UtfToUtfProc(
     dstEnd = dst + dstLen - TCL_UTF_MAX;
 
     for (numChars = 0; src < srcEnd && numChars <= charLimit; numChars++) {
-	if ((src > srcClose) && (!Tcl_UtfCharComplete(src, srcEnd - src))) {
+	if ((src > srcClose) && (!TclUCS4Complete(src, srcEnd - src))) {
 	    /*
 	     * If there is more string to follow, this will ensure that the
 	     * last UTF-8 character in the source buffer hasn't been cut off.
@@ -2349,9 +2349,9 @@ UtfToUtfProc(
 
 	    *dst++ = 0;
 	    src += 2;
-	} else if (!Tcl_UtfCharComplete(src, srcEnd - src)) {
+	} else if (!TclUCS4Complete(src, srcEnd - src)) {
 	    /*
-	     * Always check before using TclUtfToUniChar. Not doing can so
+	     * Always check before using TclUtfToUCS4. Not doing can so
 	     * cause it run beyond the end of the buffer! If we happen such an
 	     * incomplete char its bytes are made to represent themselves.
 	     */
@@ -2360,11 +2360,11 @@ UtfToUtfProc(
 	    src += 1;
 	    dst += Tcl_UniCharToUtf(*chPtr, dst);
 	} else {
-	    src += TclUtfToUniChar(src, chPtr);
+	    src += TclUtfToUCS4(src, chPtr);
 	    if ((*chPtr | 0x7FF) == 0xDFFF) {
 		/* A surrogate character is detected, handle especially */
-		Tcl_UniChar low = *chPtr;
-		size_t len = (src <= srcEnd-3) ? Tcl_UtfToUniChar(src, &low) : 0;
+		int low = *chPtr;
+		size_t len = (src <= srcEnd-3) ? TclUtfToUCS4(src, &low) : 0;
 		if (((low | 0x3FF) != 0xDFFF) || (*chPtr & 0x400)) {
 			*dst++ = (char) (((*chPtr >> 12) | 0xE0) & 0xEF);
 			*dst++ = (char) (((*chPtr >> 6) | 0x80) & 0xBF);
diff --git a/generic/tclInt.h b/generic/tclInt.h
index 2ff644e..5f660e3 100644
--- a/generic/tclInt.h
+++ b/generic/tclInt.h
@@ -3252,8 +3252,11 @@ MODULE_SCOPE int	TclUtfCasecmp(const char *cs, const char *ct);
 MODULE_SCOPE int	TclUtfCount(int ch);
 #if TCL_UTF_MAX > 3
 #   define TclUtfToUCS4 Tcl_UtfToUniChar
+#   define TclUCS4Complete Tcl_UtfCharComplete
 #else
-   MODULE_SCOPE int	TclUtfToUCS4(const char *src, int *ucs4Ptr);
+    MODULE_SCOPE int	TclUtfToUCS4(const char *src, int *ucs4Ptr);
+#   define TclUCS4Complete(src, length) (((unsigned)((unsigned char)*(src) - 0xF0) < 5) \
+	    ? ((length) >= 4) : Tcl_UtfCharComplete((src), (length)))
 #endif
 MODULE_SCOPE Tcl_Obj *	TclpNativeToNormalized(ClientData clientData);
 MODULE_SCOPE Tcl_Obj *	TclpFilesystemPathType(Tcl_Obj *pathPtr);