Allow replacement fields in format specs

Author: fanninpm

parser/src/fstring.rs

@@ -100,16 +100,19 @@ impl<'a> FStringParser<'a> {
                             '{' if in_nested => return Err(ExpressionNestedTooDeeply),
                             '}' if in_nested => {
                                 in_nested = false;
-                                spec_constructor.push(self.expr(ExprKind::FormattedValue {
-                                    value:
-                                        Box::new(
-                                            parse_fstring_expr(&formatted_value_piece).map_err(
-                                                |e| InvalidExpression(Box::new(e.error)),
-                                            )?,
+                                spec_constructor.push(
+                                    self.expr(ExprKind::FormattedValue {
+                                        value: Box::new(
+                                            FStringParser::new(
+                                                &format!("{{{}}}", formatted_value_piece),
+                                                Location::default(),
+                                            )
+                                            .parse()?,
                                         ),
-                                    conversion: None,
-                                    format_spec: None,
-                                }));
+                                        conversion: None,
+                                        format_spec: None,
+                                    }),
+                                );
                                 formatted_value_piece.clear();
                             }
                             _ if in_nested => {

parser/src/snapshots/rustpython_parser__fstring__tests__parse_fstring_nested_spec.snap

@@ -61,13 +61,35 @@ Located {
                                         node: FormattedValue {
                                             value: Located {
                                                 location: Location {
-                                                    row: 1,
-                                                    column: 2,
+                                                    row: 0,
+                                                    column: 0,
                                                 },
                                                 custom: (),
-                                                node: Name {
-                                                    id: "spec",
-                                                    ctx: Load,
+                                                node: JoinedStr {
+                                                    values: [
+                                                        Located {
+                                                            location: Location {
+                                                                row: 0,
+                                                                column: 0,
+                                                            },
+                                                            custom: (),
+                                                            node: FormattedValue {
+                                                                value: Located {
+                                                                    location: Location {
+                                                                        row: 1,
+                                                                        column: 2,
+                                                                    },
+                                                                    custom: (),
+                                                                    node: Name {
+                                                                        id: "spec",
+                                                                        ctx: Load,
+                                                                    },
+                                                                },
+                                                                conversion: None,
+                                                                format_spec: None,
+                                                            },
+                                                        },
+                                                    ],
                                                 },
                                             },
                                             conversion: None,