Refactor trailing comma rule into explicit check and state update code (#10100)

crates/ruff_linter/src/rules/flake8_commas/rules/trailing_commas.rs

@@ -29,7 +29,7 @@ enum TokenType {
 /// Simplified token specialized for the task.
 #[derive(Copy, Clone)]
 struct Token {
-    r#type: TokenType,
+    ty: TokenType,
     range: TextRange,
 }
 
@@ -40,13 +40,13 @@ impl Ranged for Token {
 }
 
 impl Token {
-    fn new(r#type: TokenType, range: TextRange) -> Self {
-        Self { r#type, range }
+    fn new(ty: TokenType, range: TextRange) -> Self {
+        Self { ty, range }
     }
 
     fn irrelevant() -> Token {
         Token {
-            r#type: TokenType::Irrelevant,
+            ty: TokenType::Irrelevant,
             range: TextRange::default(),
         }
     }
@@ -54,7 +54,7 @@ impl Token {
 
 impl From<(&Tok, TextRange)> for Token {
     fn from((tok, range): (&Tok, TextRange)) -> Self {
-        let r#type = match tok {
+        let ty = match tok {
             Tok::Name { .. } => TokenType::Named,
             Tok::String { .. } => TokenType::String,
             Tok::Newline => TokenType::Newline,
@@ -75,7 +75,7 @@ impl From<(&Tok, TextRange)> for Token {
             _ => TokenType::Irrelevant,
         };
         #[allow(clippy::inconsistent_struct_constructor)]
-        Self { range, r#type }
+        Self { range, ty }
     }
 }
 
@@ -102,16 +102,13 @@ enum ContextType {
 /// Comma context - described a comma-delimited "situation".
 #[derive(Copy, Clone)]
 struct Context {
-    r#type: ContextType,
+    ty: ContextType,
     num_commas: u32,
 }
 
 impl Context {
-    const fn new(r#type: ContextType) -> Self {
-        Self {
-            r#type,
-            num_commas: 0,
-        }
+    const fn new(ty: ContextType) -> Self {
+        Self { ty, num_commas: 0 }
     }
 
     fn inc(&mut self) {
@@ -277,9 +274,7 @@ pub(crate) fn trailing_commas(
     let mut stack = vec![Context::new(ContextType::No)];
 
     for token in tokens {
-        if prev.r#type == TokenType::NonLogicalNewline
-            && token.r#type == TokenType::NonLogicalNewline
-        {
+        if prev.ty == TokenType::NonLogicalNewline && token.ty == TokenType::NonLogicalNewline {
             // Collapse consecutive newlines to the first one -- trailing commas are
             // added before the first newline.
             continue;
@@ -288,9 +283,38 @@ pub(crate) fn trailing_commas(
         // Update the comma context stack.
         let context = update_context(token, prev, prev_prev, &mut stack);
 
+        if let Some(diagnostic) = check_token(token, prev, prev_prev, context, locator) {
+            diagnostics.push(diagnostic);
+        }
+
+        // Pop the current context if the current token ended it.
+        // The top context is never popped (if unbalanced closing brackets).
+        let pop_context = match context.ty {
+            // Lambda terminated by `:`.
+            ContextType::LambdaParameters => token.ty == TokenType::Colon,
+            // All others terminated by a closing bracket.
+            // flake8-commas doesn't verify that it matches the opening...
+            _ => token.ty == TokenType::ClosingBracket,
+        };
+        if pop_context && stack.len() > 1 {
+            stack.pop();
+        }
+
+        prev_prev = prev;
+        prev = token;
+    }
+}
+
+fn check_token(
+    token: Token,
+    prev: Token,
+    prev_prev: Token,
+    context: Context,
+    locator: &Locator,
+) -> Option<Diagnostic> {
     // Is it allowed to have a trailing comma before this token?
-        let comma_allowed = token.r#type == TokenType::ClosingBracket
-            && match context.r#type {
+    let comma_allowed = token.ty == TokenType::ClosingBracket
+        && match context.ty {
             ContextType::No => false,
             ContextType::FunctionParameters => true,
             ContextType::CallArguments => true,
@@ -305,31 +329,35 @@ pub(crate) fn trailing_commas(
         };
 
     // Is prev a prohibited trailing comma?
-        let comma_prohibited = prev.r#type == TokenType::Comma && {
+    let comma_prohibited = prev.ty == TokenType::Comma && {
         // Is `(1,)` or `x[1,]`?
         let is_singleton_tuplish =
-                matches!(context.r#type, ContextType::Subscript | ContextType::Tuple)
+            matches!(context.ty, ContextType::Subscript | ContextType::Tuple)
                 && context.num_commas <= 1;
         // There was no non-logical newline, so prohibit (except in `(1,)` or `x[1,]`).
         if comma_allowed && !is_singleton_tuplish {
             true
             // Lambdas not handled by comma_allowed so handle it specially.
         } else {
-                context.r#type == ContextType::LambdaParameters && token.r#type == TokenType::Colon
+            context.ty == ContextType::LambdaParameters && token.ty == TokenType::Colon
         }
     };
+
     if comma_prohibited {
         let mut diagnostic = Diagnostic::new(ProhibitedTrailingComma, prev.range());
         diagnostic.set_fix(Fix::safe_edit(Edit::range_deletion(diagnostic.range())));
-            diagnostics.push(diagnostic);
+        return Some(diagnostic);
     }
 
     // Is prev a prohibited trailing comma on a bare tuple?
     // Approximation: any comma followed by a statement-ending newline.
-        let bare_comma_prohibited =
-            prev.r#type == TokenType::Comma && token.r#type == TokenType::Newline;
+    let bare_comma_prohibited = prev.ty == TokenType::Comma && token.ty == TokenType::Newline;
     if bare_comma_prohibited {
-            diagnostics.push(Diagnostic::new(TrailingCommaOnBareTuple, prev.range()));
+        return Some(Diagnostic::new(TrailingCommaOnBareTuple, prev.range()));
+    }
+
+    if !comma_allowed {
+        return None;
     }
 
     // Comma is required if:
@@ -337,10 +365,9 @@ pub(crate) fn trailing_commas(
     // - Followed by a newline,
     // - Not already present,
     // - Not on an empty (), {}, [].
-        let comma_required = comma_allowed
-            && prev.r#type == TokenType::NonLogicalNewline
+    let comma_required = prev.ty == TokenType::NonLogicalNewline
         && !matches!(
-                prev_prev.r#type,
+            prev_prev.ty,
             TokenType::Comma
                 | TokenType::OpeningBracket
                 | TokenType::OpeningSquareBracket
@@ -358,24 +385,9 @@ pub(crate) fn trailing_commas(
             format!("{contents},"),
             prev_prev.range(),
         )));
-            diagnostics.push(diagnostic);
-        }
-
-        // Pop the current context if the current token ended it.
-        // The top context is never popped (if unbalanced closing brackets).
-        let pop_context = match context.r#type {
-            // Lambda terminated by `:`.
-            ContextType::LambdaParameters => token.r#type == TokenType::Colon,
-            // All others terminated by a closing bracket.
-            // flake8-commas doesn't verify that it matches the opening...
-            _ => token.r#type == TokenType::ClosingBracket,
-        };
-        if pop_context && stack.len() > 1 {
-            stack.pop();
-        }
-
-        prev_prev = prev;
-        prev = token;
+        Some(diagnostic)
+    } else {
+        None
     }
 }
 
@@ -385,15 +397,15 @@ fn update_context(
     prev_prev: Token,
     stack: &mut Vec<Context>,
 ) -> Context {
-    let new_context = match token.r#type {
-        TokenType::OpeningBracket => match (prev.r#type, prev_prev.r#type) {
+    let new_context = match token.ty {
+        TokenType::OpeningBracket => match (prev.ty, prev_prev.ty) {
             (TokenType::Named, TokenType::Def) => Context::new(ContextType::FunctionParameters),
             (TokenType::Named | TokenType::ClosingBracket, _) => {
                 Context::new(ContextType::CallArguments)
             }
             _ => Context::new(ContextType::Tuple),
         },
-        TokenType::OpeningSquareBracket => match prev.r#type {
+        TokenType::OpeningSquareBracket => match prev.ty {
             TokenType::ClosingBracket | TokenType::Named | TokenType::String => {
                 Context::new(ContextType::Subscript)
             }