Implement autofix for F541 (#1577)

resources/test/fixtures/pyflakes/F541.py

@@ -9,6 +9,14 @@ e = (
     f"def" +
     "ghi"
 )
+f = (
+    f"a"
+    F"b"
+    "c"
+    rf"d"
+    fr"e"
+)
+g = f""
 
 # OK
 g = f"ghi{123:{45}}"

src/ast/helpers.rs

@@ -9,6 +9,7 @@ use rustpython_ast::{
 };
 use rustpython_parser::lexer;
 use rustpython_parser::lexer::Tok;
+use rustpython_parser::token::StringKind;
 
 use crate::ast::types::Range;
 use crate::SourceCodeLocator;
@@ -470,6 +471,43 @@ pub fn except_range(handler: &Excepthandler, locator: &SourceCodeLocator) -> Ran
     range
 }
 
+/// Find f-strings that don't contain any formatted values in a `JoinedStr`.
+pub fn find_useless_f_strings(expr: &Expr, locator: &SourceCodeLocator) -> Vec<(Range, Range)> {
+    let contents = locator.slice_source_code_range(&Range::from_located(expr));
+    lexer::make_tokenizer_located(&contents, expr.location)
+        .flatten()
+        .filter_map(|(location, tok, end_location)| match tok {
+            Tok::String {
+                kind: StringKind::FString | StringKind::RawFString,
+                ..
+            } => {
+                let first_char = locator.slice_source_code_range(&Range {
+                    location,
+                    end_location: Location::new(location.row(), location.column() + 1),
+                });
+                // f"..."  => f_position = 0
+                // fr"..." => f_position = 0
+                // rf"..." => f_position = 1
+                let f_position = usize::from(!(first_char == "f" || first_char == "F"));
+                Some((
+                    Range {
+                        location: Location::new(location.row(), location.column() + f_position),
+                        end_location: Location::new(
+                            location.row(),
+                            location.column() + f_position + 1,
+                        ),
+                    },
+                    Range {
+                        location,
+                        end_location,
+                    },
+                ))
+            }
+            _ => None,
+        })
+        .collect()
+}
+
 /// Return the `Range` of `else` in `For`, `AsyncFor`, and `While` statements.
 pub fn else_range(stmt: &Stmt, locator: &SourceCodeLocator) -> Option<Range> {
     match &stmt.node {

src/checkers/ast.rs

@@ -2280,15 +2280,7 @@ where
             }
             ExprKind::JoinedStr { values } => {
                 if self.settings.enabled.contains(&CheckCode::F541) {
-                    if !values
-                        .iter()
-                        .any(|value| matches!(value.node, ExprKind::FormattedValue { .. }))
-                    {
-                        self.add_check(Check::new(
-                            CheckKind::FStringMissingPlaceholders,
-                            Range::from_located(expr),
-                        ));
-                    }
+                    pyflakes::plugins::f_string_missing_placeholders(expr, values, self);
                 }
             }
             ExprKind::BinOp {

src/pyflakes/plugins/f_string_missing_placeholders.rs

@@ -0,0 +1,25 @@
+use rustpython_ast::{Expr, ExprKind};
+
+use crate::ast::helpers::find_useless_f_strings;
+use crate::autofix::Fix;
+use crate::checkers::ast::Checker;
+use crate::registry::{Check, CheckCode, CheckKind};
+
+/// F541
+pub fn f_string_missing_placeholders(expr: &Expr, values: &[Expr], checker: &mut Checker) {
+    if !values
+        .iter()
+        .any(|value| matches!(value.node, ExprKind::FormattedValue { .. }))
+    {
+        for (prefix_range, tok_range) in find_useless_f_strings(expr, checker.locator) {
+            let mut check = Check::new(CheckKind::FStringMissingPlaceholders, tok_range);
+            if checker.patch(&CheckCode::F541) {
+                check.amend(Fix::deletion(
+                    prefix_range.location,
+                    prefix_range.end_location,
+                ));
+            }
+            checker.add_check(check);
+        }
+    }
+}

src/pyflakes/plugins/mod.rs

@@ -1,4 +1,5 @@
 pub use assert_tuple::assert_tuple;
+pub use f_string_missing_placeholders::f_string_missing_placeholders;
 pub use if_tuple::if_tuple;
 pub use invalid_literal_comparisons::invalid_literal_comparison;
 pub use invalid_print_syntax::invalid_print_syntax;
@@ -13,6 +14,7 @@ pub(crate) use strings::{
 };
 
 mod assert_tuple;
+mod f_string_missing_placeholders;
 mod if_tuple;
 mod invalid_literal_comparisons;
 mod invalid_print_syntax;

src/pyflakes/snapshots/ruff__pyflakes__tests__F541_F541.py.snap

@@ -9,7 +9,14 @@ expression: checks
   end_location:
     row: 6
     column: 10
-  fix: ~
+  fix:
+    content: ""
+    location:
+      row: 6
+      column: 4
+    end_location:
+      row: 6
+      column: 5
   parent: ~
 - kind: FStringMissingPlaceholders
   location:
@@ -18,7 +25,14 @@ expression: checks
   end_location:
     row: 7
     column: 10
-  fix: ~
+  fix:
+    content: ""
+    location:
+      row: 7
+      column: 4
+    end_location:
+      row: 7
+      column: 5
   parent: ~
 - kind: FStringMissingPlaceholders
   location:
@@ -27,7 +41,62 @@ expression: checks
   end_location:
     row: 9
     column: 10
-  fix: ~
+  fix:
+    content: ""
+    location:
+      row: 9
+      column: 4
+    end_location:
+      row: 9
+      column: 5
+  parent: ~
+- kind: FStringMissingPlaceholders
+  location:
+    row: 13
+    column: 4
+  end_location:
+    row: 13
+    column: 8
+  fix:
+    content: ""
+    location:
+      row: 13
+      column: 4
+    end_location:
+      row: 13
+      column: 5
+  parent: ~
+- kind: FStringMissingPlaceholders
+  location:
+    row: 14
+    column: 4
+  end_location:
+    row: 14
+    column: 8
+  fix:
+    content: ""
+    location:
+      row: 14
+      column: 4
+    end_location:
+      row: 14
+      column: 5
+  parent: ~
+- kind: FStringMissingPlaceholders
+  location:
+    row: 16
+    column: 4
+  end_location:
+    row: 16
+    column: 9
+  fix:
+    content: ""
+    location:
+      row: 16
+      column: 5
+    end_location:
+      row: 16
+      column: 6
   parent: ~
 - kind: FStringMissingPlaceholders
   location:
@@ -35,25 +104,78 @@ expression: checks
     column: 4
   end_location:
     row: 17
+    column: 9
+  fix:
+    content: ""
+    location:
+      row: 17
+      column: 4
+    end_location:
+      row: 17
+      column: 5
+  parent: ~
+- kind: FStringMissingPlaceholders
+  location:
+    row: 19
+    column: 4
+  end_location:
+    row: 19
+    column: 7
+  fix:
+    content: ""
+    location:
+      row: 19
+      column: 4
+    end_location:
+      row: 19
+      column: 5
+  parent: ~
+- kind: FStringMissingPlaceholders
+  location:
+    row: 25
+    column: 12
+  end_location:
+    row: 25
     column: 16
-  fix: ~
+  fix:
+    content: ""
+    location:
+      row: 25
+      column: 12
+    end_location:
+      row: 25
+      column: 13
   parent: ~
 - kind: FStringMissingPlaceholders
   location:
-    row: 26
+    row: 34
     column: 6
   end_location:
-    row: 26
+    row: 34
     column: 13
-  fix: ~
+  fix:
+    content: ""
+    location:
+      row: 34
+      column: 6
+    end_location:
+      row: 34
+      column: 7
   parent: ~
 - kind: FStringMissingPlaceholders
   location:
-    row: 27
+    row: 35
     column: 3
   end_location:
-    row: 27
+    row: 35
     column: 6
-  fix: ~
+  fix:
+    content: ""
+    location:
+      row: 35
+      column: 3
+    end_location:
+      row: 35
+      column: 4
   parent: ~