[Python-checkins] gh-105375: Improve error handling in compiler_enter_scope() (#105494)

[erlend-aasland]

https://github.com/python/cpython/commit/6c832ddcf28187f86100c790afb16a0223d945d0
commit: 6c832ddcf28187f86100c790afb16a0223d945d0
branch: main
author: Erlend E. Aasland <erlend.aasland at protonmail.com>
committer: erlend-aasland <erlend.aasland at protonmail.com>
date: 2023-06-09T18:55:53+02:00
summary:

gh-105375: Improve error handling in compiler_enter_scope() (#105494)

files:
A Misc/NEWS.d/next/Core and Builtins/2023-06-08-09-54-37.gh-issue-105375.kqKT3E.rst
M Python/compile.c

diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-06-08-09-54-37.gh-issue-105375.kqKT3E.rst b/Misc/NEWS.d/next/Core and Builtins/2023-06-08-09-54-37.gh-issue-105375.kqKT3E.rst
new file mode 100644
index 0000000000000..b4d3a1a5a3ced
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-06-08-09-54-37.gh-issue-105375.kqKT3E.rst	
@@ -0,0 +1 @@
+Fix bug in the compiler where an exception could end up being overwritten.
diff --git a/Python/compile.c b/Python/compile.c
index 3243172842276..e3a76236f5723 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -1228,8 +1228,12 @@ compiler_enter_scope(struct compiler *c, identifier name,
     }
     u->u_metadata.u_name = Py_NewRef(name);
     u->u_metadata.u_varnames = list2dict(u->u_ste->ste_varnames);
+    if (!u->u_metadata.u_varnames) {
+        compiler_unit_free(u);
+        return ERROR;
+    }
     u->u_metadata.u_cellvars = dictbytype(u->u_ste->ste_symbols, CELL, DEF_COMP_CELL, 0);
-    if (!u->u_metadata.u_varnames || !u->u_metadata.u_cellvars) {
+    if (!u->u_metadata.u_cellvars) {
         compiler_unit_free(u);
         return ERROR;
     }