[pyupgrade] Automatically rewrite format-strings to f-strings (#1905)

README.md

@@ -725,6 +725,7 @@ For more, see [pyupgrade](https://pypi.org/project/pyupgrade/3.2.0/) on PyPI.
 | UP028 | RewriteYieldFrom | Replace `yield` over `for` loop with `yield from` | 🛠 |
 | UP029 | UnnecessaryBuiltinImport | Unnecessary builtin import: `...` | 🛠 |
 | UP030 | FormatLiterals | Use implicit references for positional format fields | 🛠 |
+| UP032 | FString | Use f-string instead of `format` call | 🛠 |
 
 ### pep8-naming (N)
 

resources/test/fixtures/pyupgrade/UP032.py

@@ -0,0 +1,86 @@
+###
+# Errors
+###
+
+"{} {}".format(a, b)
+
+"{1} {0}".format(a, b)
+
+"{x.y}".format(x=z)
+
+"{.x} {.y}".format(a, b)
+
+"{} {}".format(a.b, c.d)
+
+"{}".format(a())
+
+"{}".format(a.b())
+
+"{}".format(a.b().c())
+
+"hello {}!".format(name)
+
+"{}{b}{}".format(a, c, b=b)
+
+"{}".format(0x0)
+
+"{} {}".format(a, b)
+
+"""{} {}""".format(a, b)
+
+"foo{}".format(1)
+
+r"foo{}".format(1)
+
+x = "{a}".format(a=1)
+
+print("foo {} ".format(x))
+
+"{a[b]}".format(a=a)
+
+"{a.a[b]}".format(a=a)
+
+"{}{{}}{}".format(escaped, y)
+
+"{}".format(a)
+
+###
+# Non-errors
+###
+
+# False-negative: RustPython doesn't parse the `\N{snowman}`.
+"\N{snowman} {}".format(a)
+
+"{".format(a)
+
+"}".format(a)
+
+"{} {}".format(*a)
+
+"{0} {0}".format(arg)
+
+"{x} {x}".format(arg)
+
+"{x.y} {x.z}".format(arg)
+
+b"{} {}".format(a, b)
+
+"{:{}}".format(x, y)
+
+"{}{}".format(a)
+
+"" "{}".format(a["\\"])
+
+"{}".format(a["b"])
+
+r'"\N{snowman} {}".format(a)'
+
+"{a}" "{b}".format(a=1, b=1)
+
+
+async def c():
+    return "{}".format(await 3)
+
+
+async def c():
+    return "{}".format(1 + await 3)

ruff.schema.json

@@ -1687,6 +1687,7 @@
         "UP029",
         "UP03",
         "UP030",
+        "UP032",
         "W",
         "W2",
         "W29",

src/checkers/ast.rs

@@ -1867,6 +1867,7 @@ where
                     || self.settings.enabled.contains(&RuleCode::F525)
                     // pyupgrade
                     || self.settings.enabled.contains(&RuleCode::UP030)
+                    || self.settings.enabled.contains(&RuleCode::UP032)
                 {
                     if let ExprKind::Attribute { value, attr, .. } = &func.node {
                         if let ExprKind::Constant {
@@ -1890,8 +1891,8 @@ where
                                     }
                                     Ok(summary) => {
                                         if self.settings.enabled.contains(&RuleCode::F522) {
-                                            pyflakes::rules::string_dot_format_extra_named_arguments(self,
-                                                                                                     &summary, keywords, location,
+                                            pyflakes::rules::string_dot_format_extra_named_arguments(
+                                                self, &summary, keywords, location,
                                             );
                                         }
 
@@ -1917,6 +1918,10 @@ where
                                         if self.settings.enabled.contains(&RuleCode::UP030) {
                                             pyupgrade::rules::format_literals(self, &summary, expr);
                                         }
+
+                                        if self.settings.enabled.contains(&RuleCode::UP032) {
+                                            pyupgrade::rules::f_strings(self, &summary, expr);
+                                        }
                                     }
                                 }
                             }

src/docstrings/constants.rs

@@ -7,3 +7,7 @@ pub const TRIPLE_QUOTE_PREFIXES: &[&str] = &[
 pub const SINGLE_QUOTE_PREFIXES: &[&str] = &[
     "u\"", "u'", "r\"", "r'", "u\"", "u'", "r\"", "r'", "U\"", "U'", "R\"", "R'", "\"", "'",
 ];
+
+pub const TRIPLE_QUOTE_SUFFIXES: &[&str] = &["\"\"\"", "'''"];
+
+pub const SINGLE_QUOTE_SUFFIXES: &[&str] = &["\"", "'"];

src/registry.rs

@@ -254,6 +254,7 @@ ruff_macros::define_rule_mapping!(
     UP028 => violations::RewriteYieldFrom,
     UP029 => violations::UnnecessaryBuiltinImport,
     UP030 => violations::FormatLiterals,
+    UP032 => violations::FString,
     // pydocstyle
     D100 => violations::PublicModule,
     D101 => violations::PublicClass,

src/rules/pydocstyle/helpers.rs

@@ -30,6 +30,14 @@ pub fn leading_quote(content: &str) -> Option<&str> {
     None
 }
 
+/// Return the trailing quote string for a docstring (e.g., `"""`).
+pub fn trailing_quote(content: &str) -> Option<&&str> {
+    constants::TRIPLE_QUOTE_SUFFIXES
+        .iter()
+        .chain(constants::SINGLE_QUOTE_SUFFIXES)
+        .find(|&pattern| content.ends_with(pattern))
+}
+
 /// Return the index of the first logical line in a string.
 pub fn logical_line(content: &str) -> Option<usize> {
     // Find the first logical line.

src/rules/pyupgrade/mod.rs

@@ -53,6 +53,7 @@ mod tests {
     #[test_case(RuleCode::UP029, Path::new("UP029.py"); "UP029")]
     #[test_case(RuleCode::UP030, Path::new("UP030_0.py"); "UP030_0")]
     #[test_case(RuleCode::UP030, Path::new("UP030_1.py"); "UP030_1")]
+    #[test_case(RuleCode::UP032, Path::new("UP032.py"); "UP032")]
     fn rules(rule_code: RuleCode, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.as_ref(), path.to_string_lossy());
         let diagnostics = test_path(

src/rules/pyupgrade/rules/f_strings.rs

@@ -0,0 +1,274 @@
+use rustc_hash::FxHashMap;
+use rustpython_ast::{Constant, Expr, ExprKind, KeywordData};
+use rustpython_common::format::{
+    FieldName, FieldNamePart, FieldType, FormatPart, FormatString, FromTemplate,
+};
+use rustpython_parser::lexer;
+use rustpython_parser::lexer::Tok;
+
+use crate::ast::types::Range;
+use crate::checkers::ast::Checker;
+use crate::fix::Fix;
+use crate::registry::{Diagnostic, RuleCode};
+use crate::rules::pydocstyle::helpers::{leading_quote, trailing_quote};
+use crate::rules::pyflakes::format::FormatSummary;
+use crate::violations;
+
+/// Like [`FormatSummary`], but maps positional and keyword arguments to their
+/// values. For example, given `{a} {b}".format(a=1, b=2)`, `FormatFunction`
+/// would include `"a"` and `'b'` in `kwargs`, mapped to `1` and `2`
+/// respectively.
+#[derive(Debug)]
+struct FormatSummaryValues<'a> {
+    args: Vec<String>,
+    kwargs: FxHashMap<&'a str, String>,
+}
+
+impl<'a> FormatSummaryValues<'a> {
+    fn try_from_expr(checker: &'a Checker, expr: &'a Expr) -> Option<Self> {
+        let mut extracted_args: Vec<String> = Vec::new();
+        let mut extracted_kwargs: FxHashMap<&str, String> = FxHashMap::default();
+        if let ExprKind::Call { args, keywords, .. } = &expr.node {
+            for arg in args {
+                let arg = checker
+                    .locator
+                    .slice_source_code_range(&Range::from_located(arg));
+                if contains_invalids(&arg) {
+                    return None;
+                }
+                extracted_args.push(arg.to_string());
+            }
+            for keyword in keywords {
+                let KeywordData { arg, value } = &keyword.node;
+                if let Some(key) = arg {
+                    let kwarg = checker
+                        .locator
+                        .slice_source_code_range(&Range::from_located(value));
+                    if contains_invalids(&kwarg) {
+                        return None;
+                    }
+                    extracted_kwargs.insert(key, kwarg.to_string());
+                }
+            }
+        }
+
+        if extracted_args.is_empty() && extracted_kwargs.is_empty() {
+            return None;
+        }
+
+        Some(Self {
+            args: extracted_args,
+            kwargs: extracted_kwargs,
+        })
+    }
+
+    fn consume_next(&mut self) -> Option<String> {
+        if self.args.is_empty() {
+            None
+        } else {
+            Some(self.args.remove(0))
+        }
+    }
+
+    fn consume_arg(&mut self, index: usize) -> Option<String> {
+        if self.args.len() > index {
+            Some(self.args.remove(index))
+        } else {
+            None
+        }
+    }
+
+    fn consume_kwarg(&mut self, key: &str) -> Option<String> {
+        self.kwargs.remove(key)
+    }
+}
+
+/// Return `true` if the string contains characters that are forbidden in
+/// argument identifier.
+fn contains_invalids(string: &str) -> bool {
+    string.contains('*')
+        || string.contains('\'')
+        || string.contains('"')
+        || string.contains("await")
+}
+
+/// Generate an f-string from an [`Expr`].
+fn try_convert_to_f_string(checker: &Checker, expr: &Expr) -> Option<String> {
+    let ExprKind::Call { func, .. } = &expr.node else {
+        return None;
+    };
+    let ExprKind::Attribute { value, .. } = &func.node else {
+        return None;
+    };
+    if !matches!(
+        &value.node,
+        ExprKind::Constant {
+            value: Constant::Str(..),
+            ..
+        },
+    ) {
+        return None;
+    };
+
+    let Some(mut summary) = FormatSummaryValues::try_from_expr(checker, expr) else {
+        return None;
+    };
+
+    let contents = checker
+        .locator
+        .slice_source_code_range(&Range::from_located(value));
+
+    // Tokenize: we need to avoid trying to fix implicit string concatenations.
+    if lexer::make_tokenizer(&contents)
+        .flatten()
+        .filter(|(_, tok, _)| matches!(tok, Tok::String { .. }))
+        .count()
+        > 1
+    {
+        return None;
+    }
+
+    // Strip the unicode prefix. It's redundant in Python 3, and invalid when used
+    // with f-strings.
+    let contents = if contents.starts_with('U') || contents.starts_with('u') {
+        &contents[1..]
+    } else {
+        &contents
+    };
+    if contents.is_empty() {
+        return None;
+    }
+
+    // Remove the leading and trailing quotes.
+    let Some(leading_quote) = leading_quote(contents) else {
+        return None;
+    };
+    let Some(trailing_quote) = trailing_quote(contents) else {
+        return None;
+    };
+    let contents = &contents[leading_quote.len()..contents.len() - trailing_quote.len()];
+
+    // Parse the format string.
+    let Ok(format_string) = FormatString::from_str(contents) else {
+        return None;
+    };
+
+    let mut converted = String::with_capacity(contents.len());
+    for part in format_string.format_parts {
+        match part {
+            FormatPart::Field {
+                field_name,
+                preconversion_spec,
+                format_spec,
+            } => {
+                converted.push('{');
+
+                let field = FieldName::parse(&field_name).ok()?;
+                match field.field_type {
+                    FieldType::Auto => {
+                        let Some(arg) = summary.consume_next() else {
+                            return None;
+                        };
+                        converted.push_str(&arg);
+                    }
+                    FieldType::Index(index) => {
+                        let Some(arg) = summary.consume_arg(index) else {
+                            return None;
+                        };
+                        converted.push_str(&arg);
+                    }
+                    FieldType::Keyword(name) => {
+                        let Some(arg) = summary.consume_kwarg(&name) else {
+                            return None;
+                        };
+                        converted.push_str(&arg);
+                    }
+                }
+
+                for part in field.parts {
+                    match part {
+                        FieldNamePart::Attribute(name) => {
+                            converted.push('.');
+                            converted.push_str(&name);
+                        }
+                        FieldNamePart::Index(index) => {
+                            converted.push('[');
+                            converted.push_str(index.to_string().as_str());
+                            converted.push(']');
+                        }
+                        FieldNamePart::StringIndex(index) => {
+                            converted.push('[');
+                            converted.push_str(&index);
+                            converted.push(']');
+                        }
+                    }
+                }
+
+                if let Some(preconversion_spec) = preconversion_spec {
+                    converted.push('!');
+                    converted.push(preconversion_spec);
+                }
+
+                if !format_spec.is_empty() {
+                    converted.push(':');
+                    converted.push_str(&format_spec);
+                }
+
+                converted.push('}');
+            }
+            FormatPart::Literal(value) => {
+                if value.starts_with('{') {
+                    converted.push('{');
+                }
+                converted.push_str(&value);
+                if value.ends_with('}') {
+                    converted.push('}');
+                }
+            }
+        }
+    }
+
+    // Construct the format string.
+    let mut contents = String::with_capacity(1 + converted.len());
+    contents.push('f');
+    contents.push_str(leading_quote);
+    contents.push_str(&converted);
+    contents.push_str(trailing_quote);
+    Some(contents)
+}
+
+/// UP032
+pub(crate) fn f_strings(checker: &mut Checker, summary: &FormatSummary, expr: &Expr) {
+    if summary.has_nested_parts {
+        return;
+    }
+
+    // Avoid refactoring multi-line strings.
+    if expr.location.row() != expr.end_location.unwrap().row() {
+        return;
+    }
+
+    // Currently, the only issue we know of is in LibCST:
+    // https://github.com/Instagram/LibCST/issues/846
+    let Some(contents) = try_convert_to_f_string(checker, expr) else {
+        return;
+    };
+
+    // Avoid refactors that increase the resulting string length.
+    let existing = checker
+        .locator
+        .slice_source_code_range(&Range::from_located(expr));
+    if contents.len() > existing.len() {
+        return;
+    }
+
+    let mut diagnostic = Diagnostic::new(violations::FString, Range::from_located(expr));
+    if checker.patch(&RuleCode::UP032) {
+        diagnostic.amend(Fix::replacement(
+            contents,
+            expr.location,
+            expr.end_location.unwrap(),
+        ));
+    };
+    checker.diagnostics.push(diagnostic);
+}

src/rules/pyupgrade/rules/mod.rs

@@ -2,6 +2,7 @@ pub(crate) use convert_named_tuple_functional_to_class::convert_named_tuple_func
 pub(crate) use convert_typed_dict_functional_to_class::convert_typed_dict_functional_to_class;
 pub(crate) use datetime_utc_alias::datetime_utc_alias;
 pub(crate) use deprecated_unittest_alias::deprecated_unittest_alias;
+pub(crate) use f_strings::f_strings;
 pub(crate) use format_literals::format_literals;
 pub(crate) use native_literals::native_literals;
 use once_cell::sync::Lazy;
@@ -31,7 +32,7 @@ pub(crate) use use_pep604_annotation::use_pep604_annotation;
 pub(crate) use useless_metaclass_type::useless_metaclass_type;
 pub(crate) use useless_object_inheritance::useless_object_inheritance;
 
-use crate::ast::helpers::{self};
+use crate::ast::helpers;
 use crate::ast::types::{Range, Scope, ScopeKind};
 use crate::fix::Fix;
 use crate::registry::Diagnostic;
@@ -41,6 +42,7 @@ mod convert_named_tuple_functional_to_class;
 mod convert_typed_dict_functional_to_class;
 mod datetime_utc_alias;
 mod deprecated_unittest_alias;
+mod f_strings;
 mod format_literals;
 mod native_literals;
 mod open_alias;

src/rules/pyupgrade/snapshots/ruff__rules__pyupgrade__tests__UP032_UP032.py.snap

@@ -0,0 +1,362 @@
+---
+source: src/rules/pyupgrade/mod.rs
+expression: diagnostics
+---
+- kind:
+    FString: ~
+  location:
+    row: 5
+    column: 0
+  end_location:
+    row: 5
+    column: 20
+  fix:
+    content: "f\"{a} {b}\""
+    location:
+      row: 5
+      column: 0
+    end_location:
+      row: 5
+      column: 20
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 7
+    column: 0
+  end_location:
+    row: 7
+    column: 22
+  fix:
+    content: "f\"{b} {a}\""
+    location:
+      row: 7
+      column: 0
+    end_location:
+      row: 7
+      column: 22
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 9
+    column: 0
+  end_location:
+    row: 9
+    column: 19
+  fix:
+    content: "f\"{z.y}\""
+    location:
+      row: 9
+      column: 0
+    end_location:
+      row: 9
+      column: 19
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 11
+    column: 0
+  end_location:
+    row: 11
+    column: 24
+  fix:
+    content: "f\"{a.x} {b.y}\""
+    location:
+      row: 11
+      column: 0
+    end_location:
+      row: 11
+      column: 24
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 13
+    column: 0
+  end_location:
+    row: 13
+    column: 24
+  fix:
+    content: "f\"{a.b} {c.d}\""
+    location:
+      row: 13
+      column: 0
+    end_location:
+      row: 13
+      column: 24
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 15
+    column: 0
+  end_location:
+    row: 15
+    column: 16
+  fix:
+    content: "f\"{a()}\""
+    location:
+      row: 15
+      column: 0
+    end_location:
+      row: 15
+      column: 16
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 17
+    column: 0
+  end_location:
+    row: 17
+    column: 18
+  fix:
+    content: "f\"{a.b()}\""
+    location:
+      row: 17
+      column: 0
+    end_location:
+      row: 17
+      column: 18
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 19
+    column: 0
+  end_location:
+    row: 19
+    column: 22
+  fix:
+    content: "f\"{a.b().c()}\""
+    location:
+      row: 19
+      column: 0
+    end_location:
+      row: 19
+      column: 22
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 21
+    column: 0
+  end_location:
+    row: 21
+    column: 24
+  fix:
+    content: "f\"hello {name}!\""
+    location:
+      row: 21
+      column: 0
+    end_location:
+      row: 21
+      column: 24
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 23
+    column: 0
+  end_location:
+    row: 23
+    column: 27
+  fix:
+    content: "f\"{a}{b}{c}\""
+    location:
+      row: 23
+      column: 0
+    end_location:
+      row: 23
+      column: 27
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 25
+    column: 0
+  end_location:
+    row: 25
+    column: 16
+  fix:
+    content: "f\"{0x0}\""
+    location:
+      row: 25
+      column: 0
+    end_location:
+      row: 25
+      column: 16
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 27
+    column: 0
+  end_location:
+    row: 27
+    column: 20
+  fix:
+    content: "f\"{a} {b}\""
+    location:
+      row: 27
+      column: 0
+    end_location:
+      row: 27
+      column: 20
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 29
+    column: 0
+  end_location:
+    row: 29
+    column: 24
+  fix:
+    content: "f\"\"\"{a} {b}\"\"\""
+    location:
+      row: 29
+      column: 0
+    end_location:
+      row: 29
+      column: 24
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 31
+    column: 0
+  end_location:
+    row: 31
+    column: 17
+  fix:
+    content: "f\"foo{1}\""
+    location:
+      row: 31
+      column: 0
+    end_location:
+      row: 31
+      column: 17
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 33
+    column: 0
+  end_location:
+    row: 33
+    column: 18
+  fix:
+    content: "fr\"foo{1}\""
+    location:
+      row: 33
+      column: 0
+    end_location:
+      row: 33
+      column: 18
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 35
+    column: 4
+  end_location:
+    row: 35
+    column: 21
+  fix:
+    content: "f\"{1}\""
+    location:
+      row: 35
+      column: 4
+    end_location:
+      row: 35
+      column: 21
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 37
+    column: 6
+  end_location:
+    row: 37
+    column: 25
+  fix:
+    content: "f\"foo {x} \""
+    location:
+      row: 37
+      column: 6
+    end_location:
+      row: 37
+      column: 25
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 39
+    column: 0
+  end_location:
+    row: 39
+    column: 20
+  fix:
+    content: "f\"{a[b]}\""
+    location:
+      row: 39
+      column: 0
+    end_location:
+      row: 39
+      column: 20
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 41
+    column: 0
+  end_location:
+    row: 41
+    column: 22
+  fix:
+    content: "f\"{a.a[b]}\""
+    location:
+      row: 41
+      column: 0
+    end_location:
+      row: 41
+      column: 22
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 43
+    column: 0
+  end_location:
+    row: 43
+    column: 29
+  fix:
+    content: "f\"{escaped}{{}}{y}\""
+    location:
+      row: 43
+      column: 0
+    end_location:
+      row: 43
+      column: 29
+  parent: ~
+- kind:
+    FString: ~
+  location:
+    row: 45
+    column: 0
+  end_location:
+    row: 45
+    column: 14
+  fix:
+    content: "f\"{a}\""
+    location:
+      row: 45
+      column: 0
+    end_location:
+      row: 45
+      column: 14
+  parent: ~
+

src/source_code/stylist.rs

@@ -61,6 +61,15 @@ impl Default for Quote {
     }
 }
 
+impl From<Quote> for char {
+    fn from(val: Quote) -> Self {
+        match val {
+            Quote::Single => '\'',
+            Quote::Double => '"',
+        }
+    }
+}
+
 impl From<&Quote> for vendor::str::Quote {
     fn from(val: &Quote) -> Self {
         match val {

src/violations.rs

@@ -3797,6 +3797,23 @@ impl AlwaysAutofixableViolation for FormatLiterals {
     }
 }
 
+define_violation!(
+    pub struct FString;
+);
+impl AlwaysAutofixableViolation for FString {
+    fn message(&self) -> String {
+        "Use f-string instead of `format` call".to_string()
+    }
+
+    fn autofix_title(&self) -> String {
+        "Convert to f-string".to_string()
+    }
+
+    fn placeholder() -> Self {
+        FString
+    }
+}
+
 // pydocstyle
 
 define_violation!(