Canonicalize f-string field spacing in annotations (#9077)

Ignore incidental formatted-value whitespace while retaining brace-leading safeguards and literal/debug text. Include compile-only annotation-constant coverage.

Assisted-by: OpenAI Codex:model identifier unavailable

crates/codegen/src/unparse.rs

@@ -628,19 +628,7 @@ impl<'a, 'b, 'c> Unparser<'a, 'b, 'c> {
             // put a space to avoid escaping the bracket
             "{ "
         } else {
-            // Preserve leading whitespace between '{' and the expression
-            let source_text = self.source.source_text();
-            let start = val.range().start().to_usize();
-            if start > 0
-                && source_text
-                    .as_bytes()
-                    .get(start - 1)
-                    .is_some_and(|b| b.is_ascii_whitespace())
-            {
-                "{ "
-            } else {
-                "{"
-            }
+            "{"
         };
         self.p(brace)?;
         self.p(&buffered)?;

extra_tests/snippets/syntax_annotations.py

@@ -1,5 +1,18 @@
 from typing import get_type_hints
 
+# Future f-string annotations canonicalize fields, not their literal padding.
+for formatted, expected in (
+    ("f'{ value }'", "f'{value}'"),
+    ("f'{ value = }'", "f' value = {value!r}'"),
+    ("f'{ value : >8}'", "f'{value: >8}'"),
+    ("f'{ {1, 2} }'", "f'{ {1, 2}}'"),
+):
+    formatted_code = compile(
+        "from __future__ import annotations\nx: " + formatted, "<test>", "exec"
+    )
+    assert expected in formatted_code.co_consts
+
+
 def func(s: str) -> int:
     return int(s)