Slice source code instead of generating it for EM fixes

crates/ruff_linter/resources/test/fixtures/flake8_errmsg/EM.py

@@ -58,3 +58,7 @@ def f_fix_indentation_check(foo):
 # Report these, but don't fix them
 if foo: raise RuntimeError("This is an example exception")
 if foo: x = 1; raise RuntimeError("This is an example exception")
+
+
+def f_triple_quoted_string():
+    raise RuntimeError(f"""This is an {"example"} exception""")

crates/ruff_linter/src/rules/flake8_errmsg/rules/string_in_exception.rs

@@ -1,10 +1,11 @@
-use ruff_python_ast::{self as ast, Arguments, Constant, Expr, ExprContext, Stmt};
-use ruff_text_size::{Ranged, TextRange};
+use ruff_python_ast::{self as ast, Arguments, Constant, Expr, Stmt};
+use ruff_source_file::Locator;
+use ruff_text_size::Ranged;
 
 use ruff_diagnostics::{Diagnostic, Edit, Fix, FixKind, Violation};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::whitespace;
-use ruff_python_codegen::{Generator, Stylist};
+use ruff_python_codegen::Stylist;
 
 use crate::checkers::ast::Checker;
 use crate::registry::{AsRule, Rule};
@@ -200,7 +201,7 @@ pub(crate) fn string_in_exception(checker: &mut Checker, stmt: &Stmt, exc: &Expr
                                             first,
                                             indentation,
                                             checker.stylist(),
-                                            checker.generator(),
+                                            checker.locator(),
                                         ));
                                     }
                                 }
@@ -223,7 +224,7 @@ pub(crate) fn string_in_exception(checker: &mut Checker, stmt: &Stmt, exc: &Expr
                                         first,
                                         indentation,
                                         checker.stylist(),
-                                        checker.generator(),
+                                        checker.locator(),
                                     ));
                                 }
                             }
@@ -250,7 +251,7 @@ pub(crate) fn string_in_exception(checker: &mut Checker, stmt: &Stmt, exc: &Expr
                                                 first,
                                                 indentation,
                                                 checker.stylist(),
-                                                checker.generator(),
+                                                checker.locator(),
                                             ));
                                         }
                                     }
@@ -281,23 +282,13 @@ fn generate_fix(
     exc_arg: &Expr,
     indentation: &str,
     stylist: &Stylist,
-    generator: Generator,
+    locator: &Locator,
 ) -> Fix {
-    let assignment = Stmt::Assign(ast::StmtAssign {
-        targets: vec![Expr::Name(ast::ExprName {
-            id: "msg".into(),
-            ctx: ExprContext::Store,
-            range: TextRange::default(),
-        })],
-        value: Box::new(exc_arg.clone()),
-        range: TextRange::default(),
-    });
-
     Fix::suggested_edits(
         Edit::insertion(
             format!(
-                "{}{}{}",
-                generator.stmt(&assignment),
+                "msg = {}{}{}",
+                locator.slice(exc_arg.range()),
                 stylist.line_ending().as_str(),
                 indentation,
             ),

crates/ruff_linter/src/rules/flake8_errmsg/snapshots/ruff_linter__rules__flake8_errmsg__tests__custom.snap

@@ -177,4 +177,20 @@ EM.py:60:35: EM101 Exception must not use a string literal, assign to variable f
    |
    = help: Assign to variable; remove string literal
 
+EM.py:64:24: EM102 [*] Exception must not use an f-string literal, assign to variable first
+   |
+63 | def f_triple_quoted_string():
+64 |     raise RuntimeError(f"""This is an {"example"} exception""")
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ EM102
+   |
+   = help: Assign to variable; remove f-string literal
+
+ℹ Suggested fix
+61 61 | 
+62 62 | 
+63 63 | def f_triple_quoted_string():
+64    |-    raise RuntimeError(f"""This is an {"example"} exception""")
+   64 |+    msg = f"""This is an {"example"} exception"""
+   65 |+    raise RuntimeError(msg)
+
 

crates/ruff_linter/src/rules/flake8_errmsg/snapshots/ruff_linter__rules__flake8_errmsg__tests__defaults.snap

@@ -215,4 +215,20 @@ EM.py:60:35: EM101 Exception must not use a string literal, assign to variable f
    |
    = help: Assign to variable; remove string literal
 
+EM.py:64:24: EM102 [*] Exception must not use an f-string literal, assign to variable first
+   |
+63 | def f_triple_quoted_string():
+64 |     raise RuntimeError(f"""This is an {"example"} exception""")
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ EM102
+   |
+   = help: Assign to variable; remove f-string literal
+
+ℹ Suggested fix
+61 61 | 
+62 62 | 
+63 63 | def f_triple_quoted_string():
+64    |-    raise RuntimeError(f"""This is an {"example"} exception""")
+   64 |+    msg = f"""This is an {"example"} exception"""
+   65 |+    raise RuntimeError(msg)
+