Add autofix for PIE800 (#8668)

## Summary

This adds an autofix for PIE800 (unnecessary spread) -- whenever we see
a `**{...}` inside another dictionary literal, just delete the `**{` and
`}` to inline the key-value pairs. So `{"a": "b", **{"c": "d"}}` becomes
just `{"a": "b", "c": "d"}`.

I have enabled this just for preview mode.

## Test Plan

Updated the preview snapshot test.

crates/ruff_linter/resources/test/fixtures/flake8_pie/PIE800.py

@@ -1,9 +1,21 @@
 {"foo": 1, **{"bar": 1}}  # PIE800
 
+{**{"bar": 10}, "a": "b"}  # PIE800
+
 foo({**foo, **{"bar": True}})  # PIE800
 
 {**foo, **{"bar": 10}}  # PIE800
 
+{ # PIE800
+    "a": "b",
+    # Preserve
+    **{
+        # all
+        "bar": 10,  # the
+        # comments
+    },
+}
+
 {**foo, **buzz, **{bar: 10}}  # PIE800
 
 {**foo,    "bar": True  }  # OK

crates/ruff_linter/src/checkers/ast/analyze/expression.rs

@@ -936,21 +936,15 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
                 flake8_trio::rules::zero_sleep_call(checker, call);
             }
         }
-        Expr::Dict(
-            dict @ ast::ExprDict {
-                keys,
-                values,
-                range: _,
-            },
-        ) => {
+        Expr::Dict(dict) => {
             if checker.any_enabled(&[
                 Rule::MultiValueRepeatedKeyLiteral,
                 Rule::MultiValueRepeatedKeyVariable,
             ]) {
                 pyflakes::rules::repeated_keys(checker, dict);
             }
             if checker.enabled(Rule::UnnecessarySpread) {
-                flake8_pie::rules::unnecessary_spread(checker, keys, values);
+                flake8_pie::rules::unnecessary_spread(checker, dict);
             }
         }
         Expr::Set(ast::ExprSet { elts, range: _ }) => {

crates/ruff_linter/src/rules/flake8_pie/mod.rs

@@ -32,6 +32,7 @@ mod tests {
     }
 
     #[test_case(Rule::UnnecessaryPlaceholder, Path::new("PIE790.py"))]
+    #[test_case(Rule::UnnecessarySpread, Path::new("PIE800.py"))]
     #[test_case(Rule::ReimplementedContainerBuiltin, Path::new("PIE807.py"))]
     fn preview_rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!(

crates/ruff_linter/src/rules/flake8_pie/rules/unnecessary_spread.rs

@@ -1,9 +1,10 @@
-use ruff_python_ast::Expr;
+use ruff_python_ast::{self as ast, Expr};
 
-use ruff_diagnostics::Diagnostic;
-use ruff_diagnostics::Violation;
+use ruff_diagnostics::{Diagnostic, Edit, Fix, FixAvailability, Violation};
 use ruff_macros::{derive_message_formats, violation};
-use ruff_text_size::Ranged;
+use ruff_python_trivia::{SimpleTokenKind, SimpleTokenizer};
+use ruff_source_file::Locator;
+use ruff_text_size::{Ranged, TextSize};
 
 use crate::checkers::ast::Checker;
 
@@ -32,22 +33,76 @@ use crate::checkers::ast::Checker;
 pub struct UnnecessarySpread;
 
 impl Violation for UnnecessarySpread {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
     #[derive_message_formats]
     fn message(&self) -> String {
         format!("Unnecessary spread `**`")
     }
+
+    fn fix_title(&self) -> Option<String> {
+        Some(format!("Remove unnecessary dict"))
+    }
 }
 
 /// PIE800
-pub(crate) fn unnecessary_spread(checker: &mut Checker, keys: &[Option<Expr>], values: &[Expr]) {
-    for item in keys.iter().zip(values.iter()) {
+pub(crate) fn unnecessary_spread(checker: &mut Checker, dict: &ast::ExprDict) {
+    // The first "end" is the start of the dictionary, immediately following the open bracket.
+    let mut prev_end = dict.start() + TextSize::from(1);
+    for item in dict.keys.iter().zip(dict.values.iter()) {
         if let (None, value) = item {
             // We only care about when the key is None which indicates a spread `**`
             // inside a dict.
-            if let Expr::Dict(_) = value {
-                let diagnostic = Diagnostic::new(UnnecessarySpread, value.range());
+            if let Expr::Dict(inner) = value {
+                let mut diagnostic = Diagnostic::new(UnnecessarySpread, value.range());
+                if checker.settings.preview.is_enabled() {
+                    if let Some(fix) = unnecessary_spread_fix(inner, prev_end, checker.locator()) {
+                        diagnostic.set_fix(fix);
+                    }
+                }
                 checker.diagnostics.push(diagnostic);
             }
         }
+        prev_end = item.1.end();
+    }
+}
+
+/// Generate a [`Fix`] to remove an unnecessary dictionary spread.
+fn unnecessary_spread_fix(
+    dict: &ast::ExprDict,
+    prev_end: TextSize,
+    locator: &Locator,
+) -> Option<Fix> {
+    // Find the `**` token preceding the spread.
+    let doublestar = SimpleTokenizer::starts_at(prev_end, locator.contents())
+        .find(|tok| matches!(tok.kind(), SimpleTokenKind::DoubleStar))?;
+
+    if let Some(last) = dict.values.last() {
+        // Ex) `**{a: 1, b: 2}`
+        let mut edits = vec![];
+        for tok in SimpleTokenizer::starts_at(last.end(), locator.contents()).skip_trivia() {
+            match tok.kind() {
+                SimpleTokenKind::Comma => {
+                    edits.push(Edit::range_deletion(tok.range()));
+                }
+                SimpleTokenKind::RBrace => {
+                    edits.push(Edit::range_deletion(tok.range()));
+                    break;
+                }
+                _ => {}
+            }
+        }
+        Some(Fix::safe_edits(
+            // Delete the first `**{`
+            Edit::deletion(doublestar.start(), dict.start() + TextSize::from(1)),
+            // Delete the trailing `}`
+            edits,
+        ))
+    } else {
+        // Ex) `**{}`
+        Some(Fix::safe_edit(Edit::deletion(
+            doublestar.start(),
+            dict.end(),
+        )))
     }
 }

crates/ruff_linter/src/rules/flake8_pie/snapshots/ruff_linter__rules__flake8_pie__tests__PIE800_PIE800.py.snap

@@ -6,37 +6,67 @@ PIE800.py:1:14: PIE800 Unnecessary spread `**`
 1 | {"foo": 1, **{"bar": 1}}  # PIE800
   |              ^^^^^^^^^^ PIE800
 2 | 
-3 | foo({**foo, **{"bar": True}})  # PIE800
+3 | {**{"bar": 10}, "a": "b"}  # PIE800
   |
+  = help: Remove unnecessary dict
 
-PIE800.py:3:15: PIE800 Unnecessary spread `**`
+PIE800.py:3:4: PIE800 Unnecessary spread `**`
   |
 1 | {"foo": 1, **{"bar": 1}}  # PIE800
 2 | 
-3 | foo({**foo, **{"bar": True}})  # PIE800
-  |               ^^^^^^^^^^^^^ PIE800
+3 | {**{"bar": 10}, "a": "b"}  # PIE800
+  |    ^^^^^^^^^^^ PIE800
 4 | 
-5 | {**foo, **{"bar": 10}}  # PIE800
+5 | foo({**foo, **{"bar": True}})  # PIE800
   |
+  = help: Remove unnecessary dict
 
-PIE800.py:5:11: PIE800 Unnecessary spread `**`
+PIE800.py:5:15: PIE800 Unnecessary spread `**`
   |
-3 | foo({**foo, **{"bar": True}})  # PIE800
+3 | {**{"bar": 10}, "a": "b"}  # PIE800
 4 | 
-5 | {**foo, **{"bar": 10}}  # PIE800
-  |           ^^^^^^^^^^^ PIE800
+5 | foo({**foo, **{"bar": True}})  # PIE800
+  |               ^^^^^^^^^^^^^ PIE800
 6 | 
-7 | {**foo, **buzz, **{bar: 10}}  # PIE800
+7 | {**foo, **{"bar": 10}}  # PIE800
   |
+  = help: Remove unnecessary dict
 
-PIE800.py:7:19: PIE800 Unnecessary spread `**`
+PIE800.py:7:11: PIE800 Unnecessary spread `**`
   |
-5 | {**foo, **{"bar": 10}}  # PIE800
+5 | foo({**foo, **{"bar": True}})  # PIE800
 6 | 
-7 | {**foo, **buzz, **{bar: 10}}  # PIE800
-  |                   ^^^^^^^^^ PIE800
+7 | {**foo, **{"bar": 10}}  # PIE800
+  |           ^^^^^^^^^^^ PIE800
 8 | 
-9 | {**foo,    "bar": True  }  # OK
+9 | { # PIE800
   |
+  = help: Remove unnecessary dict
+
+PIE800.py:12:7: PIE800 Unnecessary spread `**`
+   |
+10 |       "a": "b",
+11 |       # Preserve
+12 |       **{
+   |  _______^
+13 | |         # all
+14 | |         "bar": 10,  # the
+15 | |         # comments
+16 | |     },
+   | |_____^ PIE800
+17 |   }
+   |
+   = help: Remove unnecessary dict
+
+PIE800.py:19:19: PIE800 Unnecessary spread `**`
+   |
+17 | }
+18 | 
+19 | {**foo, **buzz, **{bar: 10}}  # PIE800
+   |                   ^^^^^^^^^ PIE800
+20 | 
+21 | {**foo,    "bar": True  }  # OK
+   |
+   = help: Remove unnecessary dict
 
 

crates/ruff_linter/src/rules/flake8_pie/snapshots/ruff_linter__rules__flake8_pie__tests__preview__PIE800_PIE800.py.snap

@@ -0,0 +1,134 @@
+---
+source: crates/ruff_linter/src/rules/flake8_pie/mod.rs
+---
+PIE800.py:1:14: PIE800 [*] Unnecessary spread `**`
+  |
+1 | {"foo": 1, **{"bar": 1}}  # PIE800
+  |              ^^^^^^^^^^ PIE800
+2 | 
+3 | {**{"bar": 10}, "a": "b"}  # PIE800
+  |
+  = help: Remove unnecessary dict
+
+ℹ Safe fix
+1   |-{"foo": 1, **{"bar": 1}}  # PIE800
+  1 |+{"foo": 1, "bar": 1}  # PIE800
+2 2 | 
+3 3 | {**{"bar": 10}, "a": "b"}  # PIE800
+4 4 | 
+
+PIE800.py:3:4: PIE800 [*] Unnecessary spread `**`
+  |
+1 | {"foo": 1, **{"bar": 1}}  # PIE800
+2 | 
+3 | {**{"bar": 10}, "a": "b"}  # PIE800
+  |    ^^^^^^^^^^^ PIE800
+4 | 
+5 | foo({**foo, **{"bar": True}})  # PIE800
+  |
+  = help: Remove unnecessary dict
+
+ℹ Safe fix
+1 1 | {"foo": 1, **{"bar": 1}}  # PIE800
+2 2 | 
+3   |-{**{"bar": 10}, "a": "b"}  # PIE800
+  3 |+{"bar": 10, "a": "b"}  # PIE800
+4 4 | 
+5 5 | foo({**foo, **{"bar": True}})  # PIE800
+6 6 | 
+
+PIE800.py:5:15: PIE800 [*] Unnecessary spread `**`
+  |
+3 | {**{"bar": 10}, "a": "b"}  # PIE800
+4 | 
+5 | foo({**foo, **{"bar": True}})  # PIE800
+  |               ^^^^^^^^^^^^^ PIE800
+6 | 
+7 | {**foo, **{"bar": 10}}  # PIE800
+  |
+  = help: Remove unnecessary dict
+
+ℹ Safe fix
+2 2 | 
+3 3 | {**{"bar": 10}, "a": "b"}  # PIE800
+4 4 | 
+5   |-foo({**foo, **{"bar": True}})  # PIE800
+  5 |+foo({**foo, "bar": True})  # PIE800
+6 6 | 
+7 7 | {**foo, **{"bar": 10}}  # PIE800
+8 8 | 
+
+PIE800.py:7:11: PIE800 [*] Unnecessary spread `**`
+  |
+5 | foo({**foo, **{"bar": True}})  # PIE800
+6 | 
+7 | {**foo, **{"bar": 10}}  # PIE800
+  |           ^^^^^^^^^^^ PIE800
+8 | 
+9 | { # PIE800
+  |
+  = help: Remove unnecessary dict
+
+ℹ Safe fix
+4 4 | 
+5 5 | foo({**foo, **{"bar": True}})  # PIE800
+6 6 | 
+7   |-{**foo, **{"bar": 10}}  # PIE800
+  7 |+{**foo, "bar": 10}  # PIE800
+8 8 | 
+9 9 | { # PIE800
+10 10 |     "a": "b",
+
+PIE800.py:12:7: PIE800 [*] Unnecessary spread `**`
+   |
+10 |       "a": "b",
+11 |       # Preserve
+12 |       **{
+   |  _______^
+13 | |         # all
+14 | |         "bar": 10,  # the
+15 | |         # comments
+16 | |     },
+   | |_____^ PIE800
+17 |   }
+   |
+   = help: Remove unnecessary dict
+
+ℹ Safe fix
+9  9  | { # PIE800
+10 10 |     "a": "b",
+11 11 |     # Preserve
+12    |-    **{
+   12 |+    
+13 13 |         # all
+14    |-        "bar": 10,  # the
+   14 |+        "bar": 10  # the
+15 15 |         # comments
+16    |-    },
+   16 |+    ,
+17 17 | }
+18 18 | 
+19 19 | {**foo, **buzz, **{bar: 10}}  # PIE800
+
+PIE800.py:19:19: PIE800 [*] Unnecessary spread `**`
+   |
+17 | }
+18 | 
+19 | {**foo, **buzz, **{bar: 10}}  # PIE800
+   |                   ^^^^^^^^^ PIE800
+20 | 
+21 | {**foo,    "bar": True  }  # OK
+   |
+   = help: Remove unnecessary dict
+
+ℹ Safe fix
+16 16 |     },
+17 17 | }
+18 18 | 
+19    |-{**foo, **buzz, **{bar: 10}}  # PIE800
+   19 |+{**foo, **buzz, bar: 10}  # PIE800
+20 20 | 
+21 21 | {**foo,    "bar": True  }  # OK
+22 22 | 
+
+