1 files changed, 58 insertions, 18 deletions

diff --git a/Parser/lexer/lexer.c b/Parser/lexer/lexer.c
index 98adf7447c5..0a078dd5941 100644
--- a/Parser/lexer/lexer.c
+++ b/Parser/lexer/lexer.c
@@ -405,6 +405,51 @@ tok_continuation_line(struct tok_state *tok) {
 }
 
 static int
+maybe_raise_syntax_error_for_string_prefixes(struct tok_state *tok,
+                                             int saw_b, int saw_r, int saw_u,
+                                             int saw_f, int saw_t) {
+    // Supported: rb, rf, rt (in any order)
+    // Unsupported: ub, ur, uf, ut, bf, bt, ft (in any order)
+
+#define RETURN_SYNTAX_ERROR(PREFIX1, PREFIX2)                             \
+    do {                                                                  \
+        (void)_PyTokenizer_syntaxerror_known_range(                       \
+            tok, (int)(tok->start + 1 - tok->line_start),                 \
+            (int)(tok->cur - tok->line_start),                            \
+            "'" PREFIX1 "' and '" PREFIX2 "' prefixes are incompatible"); \
+        return -1;                                                        \
+    } while (0)
+
+    if (saw_u && saw_b) {
+        RETURN_SYNTAX_ERROR("u", "b");
+    }
+    if (saw_u && saw_r) {
+        RETURN_SYNTAX_ERROR("u", "r");
+    }
+    if (saw_u && saw_f) {
+        RETURN_SYNTAX_ERROR("u", "f");
+    }
+    if (saw_u && saw_t) {
+        RETURN_SYNTAX_ERROR("u", "t");
+    }
+
+    if (saw_b && saw_f) {
+        RETURN_SYNTAX_ERROR("b", "f");
+    }
+    if (saw_b && saw_t) {
+        RETURN_SYNTAX_ERROR("b", "t");
+    }
+
+    if (saw_f && saw_t) {
+        RETURN_SYNTAX_ERROR("f", "t");
+    }
+
+#undef RETURN_SYNTAX_ERROR
+
+    return 0;
+}
+
+static int
 tok_get_normal_mode(struct tok_state *tok, tokenizer_mode* current_tok, struct token *token)
 {
     int c;
@@ -648,22 +693,22 @@ tok_get_normal_mode(struct tok_state *tok, tokenizer_mode* current_tok, struct t
         /* Process the various legal combinations of b"", r"", u"", and f"". */
         int saw_b = 0, saw_r = 0, saw_u = 0, saw_f = 0, saw_t = 0;
         while (1) {
-            if (!(saw_b || saw_u || saw_f) && (c == 'b' || c == 'B'))
+            if (!saw_b && (c == 'b' || c == 'B')) {
                 saw_b = 1;
+            }
             /* Since this is a backwards compatibility support literal we don't
                want to support it in arbitrary order like byte literals. */
-            else if (!(saw_b || saw_u || saw_r || saw_f || saw_t)
-                     && (c == 'u'|| c == 'U')) {
+            else if (!saw_u && (c == 'u'|| c == 'U')) {
                 saw_u = 1;
             }
             /* ur"" and ru"" are not supported */
-            else if (!(saw_r || saw_u) && (c == 'r' || c == 'R')) {
+            else if (!saw_r && (c == 'r' || c == 'R')) {
                 saw_r = 1;
             }
-            else if (!(saw_f || saw_b || saw_u) && (c == 'f' || c == 'F')) {
+            else if (!saw_f && (c == 'f' || c == 'F')) {
                 saw_f = 1;
             }
-            else if (!(saw_t || saw_u) && (c == 't' || c == 'T')) {
+            else if (!saw_t && (c == 't' || c == 'T')) {
                 saw_t = 1;
             }
             else {
@@ -671,17 +716,11 @@ tok_get_normal_mode(struct tok_state *tok, tokenizer_mode* current_tok, struct t
             }
             c = tok_nextc(tok);
             if (c == '"' || c == '\'') {
-                if (saw_b && saw_t) {
-                    return MAKE_TOKEN(_PyTokenizer_syntaxerror_known_range(
-                        tok, (int)(tok->start + 1 - tok->line_start),
-                        (int)(tok->cur - tok->line_start),
-                        "can't use 'b' and 't' string prefixes together"));
-                }
-                if (saw_f && saw_t) {
-                    return MAKE_TOKEN(_PyTokenizer_syntaxerror_known_range(
-                        tok, (int)(tok->start + 1 - tok->line_start),
-                        (int)(tok->cur - tok->line_start),
-                        "can't use 'f' and 't' string prefixes together"));
+                // Raise error on incompatible string prefixes:
+                int status = maybe_raise_syntax_error_for_string_prefixes(
+                    tok, saw_b, saw_r, saw_u, saw_f, saw_t);
+                if (status < 0) {
+                    return MAKE_TOKEN(ERRORTOKEN);
                 }
 
                 // Handle valid f or t string creation:
@@ -1382,7 +1421,8 @@ f_string_middle:
                     return MAKE_TOKEN(
                         _PyTokenizer_syntaxerror(
                             tok,
-                            "f-string: newlines are not allowed in format specifiers for single quoted f-strings"
+                            "%c-string: newlines are not allowed in format specifiers for single quoted %c-strings",
+                            TOK_GET_STRING_PREFIX(tok), TOK_GET_STRING_PREFIX(tok)
                         )
                     );
                 }