Fix for F541 unescape f-string (#2971)

crates/ruff/resources/test/fixtures/pyflakes/F541.py

@@ -33,3 +33,11 @@ f"{f'{v:0.2f}'}"
 # Errors
 f"{v:{f'0.2f'}}"
 f"{f''}"
+f"{{test}}"
+f'{{ 40 }}'
+f"{{a {{x}}"
+f"{{{{x}}}}"
+
+# To be fixed
+# Error: f-string: single '}' is not allowed at line 41 column 8
+# f"\{{x}}"  

crates/ruff/src/rules/pyflakes/rules/f_string_missing_placeholders.rs

@@ -2,6 +2,7 @@ use ruff_macros::{define_violation, derive_message_formats};
 use rustpython_parser::ast::{Expr, ExprKind};
 
 use crate::ast::helpers::find_useless_f_strings;
+use crate::ast::types::Range;
 use crate::checkers::ast::Checker;
 use crate::fix::Fix;
 use crate::registry::Diagnostic;
@@ -46,6 +47,26 @@ impl AlwaysAutofixableViolation for FStringMissingPlaceholders {
     }
 }
 
+fn unescape_f_string(content: &str) -> String {
+    content.replace("{{", "{").replace("}}", "}")
+}
+
+fn fix_f_string_missing_placeholders(
+    prefix_range: &Range,
+    tok_range: &Range,
+    checker: &mut Checker,
+) -> Fix {
+    let content = checker.locator.slice(&Range::new(
+        prefix_range.end_location,
+        tok_range.end_location,
+    ));
+    Fix::replacement(
+        unescape_f_string(content),
+        prefix_range.location,
+        tok_range.end_location,
+    )
+}
+
 /// F541
 pub fn f_string_missing_placeholders(expr: &Expr, values: &[Expr], checker: &mut Checker) {
     if !values
@@ -55,9 +76,10 @@ pub fn f_string_missing_placeholders(expr: &Expr, values: &[Expr], checker: &mut
         for (prefix_range, tok_range) in find_useless_f_strings(expr, checker.locator) {
             let mut diagnostic = Diagnostic::new(FStringMissingPlaceholders, tok_range);
             if checker.patch(diagnostic.kind.rule()) {
-                diagnostic.amend(Fix::deletion(
-                    prefix_range.location,
-                    prefix_range.end_location,
+                diagnostic.amend(fix_f_string_missing_placeholders(
+                    &prefix_range,
+                    &tok_range,
+                    checker,
                 ));
             }
             checker.diagnostics.push(diagnostic);

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F541_F541.py.snap

@@ -1,5 +1,5 @@
 ---
-source: src/rules/pyflakes/mod.rs
+source: crates/ruff/src/rules/pyflakes/mod.rs
 expression: diagnostics
 ---
 - kind:
@@ -12,13 +12,13 @@ expression: diagnostics
     column: 10
   fix:
     content:
-      - ""
+      - "\"def\""
     location:
       row: 6
       column: 4
     end_location:
       row: 6
-      column: 5
+      column: 10
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -30,13 +30,13 @@ expression: diagnostics
     column: 10
   fix:
     content:
-      - ""
+      - "\"def\""
     location:
       row: 7
       column: 4
     end_location:
       row: 7
-      column: 5
+      column: 10
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -48,13 +48,13 @@ expression: diagnostics
     column: 10
   fix:
     content:
-      - ""
+      - "\"def\""
     location:
       row: 9
       column: 4
     end_location:
       row: 9
-      column: 5
+      column: 10
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -66,13 +66,13 @@ expression: diagnostics
     column: 8
   fix:
     content:
-      - ""
+      - "\"a\""
     location:
       row: 13
       column: 4
     end_location:
       row: 13
-      column: 5
+      column: 8
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -84,13 +84,13 @@ expression: diagnostics
     column: 8
   fix:
     content:
-      - ""
+      - "\"b\""
     location:
       row: 14
       column: 4
     end_location:
       row: 14
-      column: 5
+      column: 8
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -102,13 +102,13 @@ expression: diagnostics
     column: 9
   fix:
     content:
-      - ""
+      - "\"d\""
     location:
       row: 16
       column: 5
     end_location:
       row: 16
-      column: 6
+      column: 9
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -120,13 +120,13 @@ expression: diagnostics
     column: 9
   fix:
     content:
-      - ""
+      - "r\"e\""
     location:
       row: 17
       column: 4
     end_location:
       row: 17
-      column: 5
+      column: 9
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -138,13 +138,13 @@ expression: diagnostics
     column: 7
   fix:
     content:
-      - ""
+      - "\"\""
     location:
       row: 19
       column: 4
     end_location:
       row: 19
-      column: 5
+      column: 7
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -156,13 +156,13 @@ expression: diagnostics
     column: 16
   fix:
     content:
-      - ""
+      - "\"z\""
     location:
       row: 25
       column: 12
     end_location:
       row: 25
-      column: 13
+      column: 16
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -174,13 +174,13 @@ expression: diagnostics
     column: 13
   fix:
     content:
-      - ""
+      - "'0.2f'"
     location:
       row: 34
       column: 6
     end_location:
       row: 34
-      column: 7
+      column: 13
   parent: ~
 - kind:
     FStringMissingPlaceholders: ~
@@ -192,12 +192,84 @@ expression: diagnostics
     column: 6
   fix:
     content:
-      - ""
+      - "''"
     location:
       row: 35
       column: 3
     end_location:
       row: 35
-      column: 4
+      column: 6
+  parent: ~
+- kind:
+    FStringMissingPlaceholders: ~
+  location:
+    row: 36
+    column: 0
+  end_location:
+    row: 36
+    column: 11
+  fix:
+    content:
+      - "\"{test}\""
+    location:
+      row: 36
+      column: 0
+    end_location:
+      row: 36
+      column: 11
+  parent: ~
+- kind:
+    FStringMissingPlaceholders: ~
+  location:
+    row: 37
+    column: 0
+  end_location:
+    row: 37
+    column: 11
+  fix:
+    content:
+      - "'{ 40 }'"
+    location:
+      row: 37
+      column: 0
+    end_location:
+      row: 37
+      column: 11
+  parent: ~
+- kind:
+    FStringMissingPlaceholders: ~
+  location:
+    row: 38
+    column: 0
+  end_location:
+    row: 38
+    column: 12
+  fix:
+    content:
+      - "\"{a {x}\""
+    location:
+      row: 38
+      column: 0
+    end_location:
+      row: 38
+      column: 12
+  parent: ~
+- kind:
+    FStringMissingPlaceholders: ~
+  location:
+    row: 39
+    column: 0
+  end_location:
+    row: 39
+    column: 12
+  fix:
+    content:
+      - "\"{{x}}\""
+    location:
+      row: 39
+      column: 0
+    end_location:
+      row: 39
+      column: 12
   parent: ~