make too many nested blocks be a SyntaxError instead of a SystemError (closes #27514)

Patch by Ammar Askar.

Author: benjaminp

Lib/test/test_syntax.py

@@ -342,7 +342,9 @@
      ...
    SyntaxError: 'break' outside loop
 
-This should probably raise a better error than a SystemError (or none at all).
+This raises a SyntaxError, it used to raise a SystemError.
+Context for this change can be found on issue #27514
+
 In 2.5 there was a missing exception and an assert was triggered in a debug
 build.  The number of blocks must be greater than CO_MAXBLOCKS.  SF #1565514
 
@@ -370,7 +372,7 @@
    ...                      break
    Traceback (most recent call last):
      ...
-   SystemError: too many statically nested blocks
+   SyntaxError: too many statically nested blocks
 
 Misuse of the nonlocal statement can lead to a few unique syntax errors.
 

Misc/NEWS

@@ -10,6 +10,9 @@ Release date: TBA
 Core and Builtins
 -----------------
 
+- Issue #27514: Make having too many statically nested blocks a SyntaxError
+  instead of SystemError.
+
 - Issue #27473: Fixed possible integer overflow in bytes and bytearray
   concatenations.  Patch by Xiang Zhang.
 

Python/compile.c

@@ -3980,7 +3980,7 @@ compiler_push_fblock(struct compiler *c, enum fblocktype t, basicblock *b)
 {
     struct fblockinfo *f;
     if (c->u->u_nfblocks >= CO_MAXBLOCKS) {
-        PyErr_SetString(PyExc_SystemError,
+        PyErr_SetString(PyExc_SyntaxError,
                         "too many statically nested blocks");
         return 0;
     }