Fix optimisation of aligned '%' formats ('%05s', '%-5s') into the correct...

Fix optimisation of aligned '%' formats ('%05s', '%-5s') into the correct f-string alignment format.
Closes https://github.com/cython/cython/issues/3476

Cython/Compiler/Optimize.py

@@ -4292,10 +4292,10 @@ class ConstantFolding(Visitor.VisitorTransform, SkipDeclarations):
         return self.visit_BinopNode(node)
 
     _parse_string_format_regex = (
-        u'(%(?:'            # %...
-        u'(?:[0-9]+|[ ])?'  # width (optional) or space prefix fill character (optional)
-        u'(?:[.][0-9]+)?'   # precision (optional)
-        u')?.)'             # format type (or something different for unsupported formats)
+        u'(%(?:'              # %...
+        u'(?:[-0-9]+|[ ])?'   # width (optional) or space prefix fill character (optional)
+        u'(?:[.][0-9]+)?'     # precision (optional)
+        u')?.)'               # format type (or something different for unsupported formats)
     )
 
     def _build_fstring(self, pos, ustring, format_args):
@@ -4334,9 +4334,15 @@ class ConstantFolding(Visitor.VisitorTransform, SkipDeclarations):
                 elif format_type in u'ars':
                     format_spec = format_spec[:-1]
                     conversion_char = format_type
+                    if format_spec.startswith('0'):
+                        format_spec = '>' + format_spec[1:]  # right-alignment '%05s' spells '{:>5}'
                 elif format_type == u'd':
                     # '%d' formatting supports float, but '{obj:d}' does not => convert to int first.
                     conversion_char = 'd'
+
+                if format_spec.startswith('-'):
+                    format_spec = '<' + format_spec[1:]  # left-alignment '%-5s' spells '{:<5}'
+
                 substrings.append(ExprNodes.FormattedValueNode(
                     arg.pos, value=arg,
                     conversion_char=conversion_char,

tests/run/fstring.pyx

@@ -478,29 +478,29 @@ def generated_fstring(int i, float f, unicode u not None, o):
     """
     >>> i, f, u, o = 11, 1.3125, u'xyz', [1]
     >>> print(((
-    ...     u"(i) %s-%.3s-%r-%.3r-%d-%3d-%o-%04o-%x-%4x-%X-%03X-%.1f-%04.2f %% "
-    ...     u"(u) %s-%.2s-%r-%.7r %% "
+    ...     u"(i) %s-%.3s-%r-%.3r-%d-%3d-%-3d-%o-%04o-%x-%4x-%X-%03X-%.1f-%04.2f %% "
+    ...     u"(u) %s-%.2s-%r-%.7r-%05s-%-5s %% "
     ...     u"(o) %s-%.2s-%r-%.2r %% "
     ...     u"(f) %.2f-%d"
     ... ) % (
-    ...     i, i, i, i, i, i, i, i, i, i, i, i, i, i,
-    ...     u, u, u, u,
+    ...     i, i, i, i, i, i, i, i, i, i, i, i, i, i, i,
+    ...     u, u, u, u, u, u,
     ...     o, o, o, o,
     ...     f, f,
     ... )).replace("-u'xyz'", "-'xyz'"))
-    (i) 11-11-11-11-11- 11-13-0013-b-   b-B-00B-11.0-11.00 % (u) xyz-xy-'xyz'-'xyz' % (o) [1]-[1-[1]-[1 % (f) 1.31-1
+    (i) 11-11-11-11-11- 11-11 -13-0013-b-   b-B-00B-11.0-11.00 % (u) xyz-xy-'xyz'-'xyz'-  xyz-xyz   % (o) [1]-[1-[1]-[1 % (f) 1.31-1
 
     >>> print(generated_fstring(i, f, u, o).replace("-u'xyz'", "-'xyz'"))
-    (i) 11-11-11-11-11- 11-13-0013-b-   b-B-00B-11.0-11.00 % (u) xyz-xy-'xyz'-'xyz' % (o) [1]-[1-[1]-[1 % (f) 1.31-1
+    (i) 11-11-11-11-11- 11-11 -13-0013-b-   b-B-00B-11.0-11.00 % (u) xyz-xy-'xyz'-'xyz'-  xyz-xyz   % (o) [1]-[1-[1]-[1 % (f) 1.31-1
     """
     return (
-        u"(i) %s-%.3s-%r-%.3r-%d-%3d-%o-%04o-%x-%4x-%X-%03X-%.1f-%04.2f %% "
-        u"(u) %s-%.2s-%r-%.7r %% "
+        u"(i) %s-%.3s-%r-%.3r-%d-%3d-%-3d-%o-%04o-%x-%4x-%X-%03X-%.1f-%04.2f %% "
+        u"(u) %s-%.2s-%r-%.7r-%05s-%-5s %% "
         u"(o) %s-%.2s-%r-%.2r %% "
         u"(f) %.2f-%d"
     ) % (
-        i, i, i, i, i, i, i, i, i, i, i, i, i, i,
-        u, u, u, u,
+        i, i, i, i, i, i, i, i, i, i, i, i, i, i, i,
+        u, u, u, u, u, u,
         o, o, o, o,
         f, f,
     )