feat: support constant folding in ExpressionChecker.check_str_format_call [1/1] (#19977)

This PR implements constant folding in
`ExpressionChecker.check_str_format_call`

Author: BobTheBuidler

mypy/checkexpr.py

@@ -18,6 +18,7 @@
 from mypy.checker_shared import ExpressionCheckerSharedApi
 from mypy.checkmember import analyze_member_access, has_operator
 from mypy.checkstrformat import StringFormatterChecker
+from mypy.constant_fold import constant_fold_expr
 from mypy.erasetype import erase_type, remove_instance_last_known_values, replace_meta_vars
 from mypy.errors import ErrorInfo, ErrorWatcher, report_internal_error
 from mypy.expandtype import (
@@ -656,11 +657,12 @@ def visit_call_expr_inner(self, e: CallExpr, allow_none_return: bool = False) ->
         return ret_type
 
     def check_str_format_call(self, e: CallExpr) -> None:
-        """More precise type checking for str.format() calls on literals."""
+        """More precise type checking for str.format() calls on literals and folded constants."""
         assert isinstance(e.callee, MemberExpr)
         format_value = None
-        if isinstance(e.callee.expr, StrExpr):
-            format_value = e.callee.expr.value
+        folded_callee_expr = constant_fold_expr(e.callee.expr, "<unused>")
+        if isinstance(folded_callee_expr, str):
+            format_value = folded_callee_expr
         elif self.chk.has_type(e.callee.expr):
             typ = get_proper_type(self.chk.lookup_type(e.callee.expr))
             if (