src/tools/rust-analyzer/crates/syntax/src/validation.rs - toolchain/rustc - Git at Google

 //! This module implements syntax validation that the parser doesn't handle.
 //!
 //! A failed validation emits a diagnostic.

 mod block;

 use crate::{
     algo,
     ast::{self, VisibilityOwner},
     match_ast, AstNode, SyntaxError,
     SyntaxKind::{CONST, FN, INT_NUMBER, TYPE_ALIAS},
     SyntaxNode, SyntaxToken, TextSize, T,
 };
 use rowan::Direction;
 use rustc_lexer::unescape::{
     self, unescape_byte, unescape_byte_literal, unescape_char, unescape_literal, Mode,
 };
 use std::convert::TryFrom;

 fn rustc_unescape_error_to_string(err: unescape::EscapeError) -> &'static str {
     use unescape::EscapeError as EE;

     #[rustfmt::skip]
     let err_message = match err {
         EE::ZeroChars => {
             "Literal must not be empty"
         }
         EE::MoreThanOneChar => {
             "Literal must be one character long"
         }
         EE::LoneSlash => {
             "Character must be escaped: `\\`"
         }
         EE::InvalidEscape => {
             "Invalid escape"
         }
         EE::BareCarriageReturn | EE::BareCarriageReturnInRawString => {
             "Character must be escaped: `\r`"
         }
         EE::EscapeOnlyChar => {
             "Escape character `\\` must be escaped itself"
         }
         EE::TooShortHexEscape => {
             "ASCII hex escape code must have exactly two digits"
         }
         EE::InvalidCharInHexEscape => {
             "ASCII hex escape code must contain only hex characters"
         }
         EE::OutOfRangeHexEscape => {
             "ASCII hex escape code must be at most 0x7F"
         }
         EE::NoBraceInUnicodeEscape => {
             "Missing `{` to begin the unicode escape"
         }
         EE::InvalidCharInUnicodeEscape => {
             "Unicode escape must contain only hex characters and underscores"
         }
         EE::EmptyUnicodeEscape => {
             "Unicode escape must not be empty"
         }
         EE::UnclosedUnicodeEscape => {
             "Missing `}` to terminate the unicode escape"
         }
         EE::LeadingUnderscoreUnicodeEscape => {
             "Unicode escape code must not begin with an underscore"
         }
         EE::OverlongUnicodeEscape => {
             "Unicode escape code must have at most 6 digits"
         }
         EE::LoneSurrogateUnicodeEscape => {
             "Unicode escape code must not be a surrogate"
         }
         EE::OutOfRangeUnicodeEscape => {
             "Unicode escape code must be at most 0x10FFFF"
         }
         EE::UnicodeEscapeInByte => {
             "Byte literals must not contain unicode escapes"
         }
         EE::NonAsciiCharInByte | EE::NonAsciiCharInByteString => {
             "Byte literals must not contain non-ASCII characters"
         }
     };

     err_message
 }

 pub(crate) fn validate(root: &SyntaxNode) -> Vec<SyntaxError> {
     // FIXME:
     // * Add unescape validation of raw string literals and raw byte string literals
     // * Add validation of doc comments are being attached to nodes

     let mut errors = Vec::new();
     for node in root.descendants() {
         match_ast! {
             match node {
                 ast::Literal(it) => validate_literal(it, &mut errors),
                 ast::Const(it) => validate_const(it, &mut errors),
                 ast::BlockExpr(it) => block::validate_block_expr(it, &mut errors),
                 ast::FieldExpr(it) => validate_numeric_name(it.name_ref(), &mut errors),
                 ast::RecordExprField(it) => validate_numeric_name(it.name_ref(), &mut errors),
                 ast::Visibility(it) => validate_visibility(it, &mut errors),
                 ast::RangeExpr(it) => validate_range_expr(it, &mut errors),
                 ast::PathSegment(it) => validate_path_keywords(it, &mut errors),
                 ast::RefType(it) => validate_trait_object_ref_ty(it, &mut errors),
                 ast::PtrType(it) => validate_trait_object_ptr_ty(it, &mut errors),
                 ast::FnPtrType(it) => validate_trait_object_fn_ptr_ret_ty(it, &mut errors),
                 ast::MacroRules(it) => validate_macro_rules(it, &mut errors),
                 _ => (),
             }
         }
     }
     errors
 }

 fn validate_literal(literal: ast::Literal, acc: &mut Vec<SyntaxError>) {
     // FIXME: move this function to outer scope (https://github.com/rust-analyzer/rust-analyzer/pull/2834#discussion_r366196658)
     fn unquote(text: &str, prefix_len: usize, end_delimiter: char) -> Option<&str> {
         text.rfind(end_delimiter).and_then(|end| text.get(prefix_len..end))
     }

     let token = literal.token();
     let text = token.text();

     // FIXME: lift this lambda refactor to `fn` (https://github.com/rust-analyzer/rust-analyzer/pull/2834#discussion_r366199205)
     let mut push_err = |prefix_len, (off, err): (usize, unescape::EscapeError)| {
         let off = token.text_range().start() + TextSize::try_from(off + prefix_len).unwrap();
         acc.push(SyntaxError::new_at_offset(rustc_unescape_error_to_string(err), off));
     };

     match literal.kind() {
         ast::LiteralKind::String(s) => {
             if !s.is_raw() {
                 if let Some(without_quotes) = unquote(text, 1, '"') {
                     unescape_literal(without_quotes, Mode::Str, &mut |range, char| {
                         if let Err(err) = char {
                             push_err(1, (range.start, err));
                         }
                     })
                 }
             }
         }
         ast::LiteralKind::ByteString(s) => {
             if !s.is_raw() {
                 if let Some(without_quotes) = unquote(text, 2, '"') {
                     unescape_byte_literal(without_quotes, Mode::ByteStr, &mut |range, char| {
                         if let Err(err) = char {
                             push_err(2, (range.start, err));
                         }
                     })
                 }
             }
         }
         ast::LiteralKind::Char => {
             if let Some(Err(e)) = unquote(text, 1, '\'').map(unescape_char) {
                 push_err(1, e);
             }
         }
         ast::LiteralKind::Byte => {
             if let Some(Err(e)) = unquote(text, 2, '\'').map(unescape_byte) {
                 push_err(2, e);
             }
         }
         ast::LiteralKind::IntNumber(_)
         | ast::LiteralKind::FloatNumber(_)
         | ast::LiteralKind::Bool(_) => {}
     }
 }

 pub(crate) fn validate_block_structure(root: &SyntaxNode) {
     let mut stack = Vec::new();
     for node in root.descendants() {
         match node.kind() {
             T!['{'] => stack.push(node),
             T!['}'] => {
                 if let Some(pair) = stack.pop() {
                     assert_eq!(
                         node.parent(),
                         pair.parent(),
                         "\nunpaired curlys:\n{}\n{:#?}\n",
                         root.text(),
                         root,
                     );
                     assert!(
                         node.next_sibling().is_none() && pair.prev_sibling().is_none(),
                         "\nfloating curlys at {:?}\nfile:\n{}\nerror:\n{}\n",
                         node,
                         root.text(),
                         node.text(),
                     );
                 }
             }
             _ => (),
         }
     }
 }

 fn validate_numeric_name(name_ref: Option<ast::NameRef>, errors: &mut Vec<SyntaxError>) {
     if let Some(int_token) = int_token(name_ref) {
         if int_token.text().chars().any(|c| !c.is_digit(10)) {
             errors.push(SyntaxError::new(
                 "Tuple (struct) field access is only allowed through \
                 decimal integers with no underscores or suffix",
                 int_token.text_range(),
             ));
         }
     }

     fn int_token(name_ref: Option<ast::NameRef>) -> Option<SyntaxToken> {
         name_ref?.syntax().first_child_or_token()?.into_token().filter(|it| it.kind() == INT_NUMBER)
     }
 }

 fn validate_visibility(vis: ast::Visibility, errors: &mut Vec<SyntaxError>) {
     let parent = match vis.syntax().parent() {
         Some(it) => it,
         None => return,
     };
     match parent.kind() {
         FN | CONST | TYPE_ALIAS => (),
         _ => return,
     }

     let impl_def = match parent.parent().and_then(|it| it.parent()).and_then(ast::Impl::cast) {
         Some(it) => it,
         None => return,
     };
     if impl_def.trait_().is_some() {
         errors.push(SyntaxError::new("Unnecessary visibility qualifier", vis.syntax.text_range()));
     }
 }

 fn validate_range_expr(expr: ast::RangeExpr, errors: &mut Vec<SyntaxError>) {
     if expr.op_kind() == Some(ast::RangeOp::Inclusive) && expr.end().is_none() {
         errors.push(SyntaxError::new(
             "An inclusive range must have an end expression",
             expr.syntax().text_range(),
         ));
     }
 }

 fn validate_path_keywords(segment: ast::PathSegment, errors: &mut Vec<SyntaxError>) {
     use ast::PathSegmentKind;

     let path = segment.parent_path();
     let is_path_start = segment.coloncolon_token().is_none() && path.qualifier().is_none();

     if let Some(token) = segment.self_token() {
         if !is_path_start {
             errors.push(SyntaxError::new(
                 "The `self` keyword is only allowed as the first segment of a path",
                 token.text_range(),
             ));
         }
     } else if let Some(token) = segment.crate_token() {
         if !is_path_start || use_prefix(path).is_some() {
             errors.push(SyntaxError::new(
                 "The `crate` keyword is only allowed as the first segment of a path",
                 token.text_range(),
             ));
         }
     } else if let Some(token) = segment.super_token() {
         if segment.coloncolon_token().is_some() || !all_supers(&path) {
             errors.push(SyntaxError::new(
                 "The `super` keyword may only be preceded by other `super`s",
                 token.text_range(),
             ));
             return;
         }

         let mut curr_path = path;
         while let Some(prefix) = use_prefix(curr_path) {
             if !all_supers(&prefix) {
                 errors.push(SyntaxError::new(
                     "The `super` keyword may only be preceded by other `super`s",
                     token.text_range(),
                 ));
                 return;
             }
             curr_path = prefix;
         }
     }

     fn use_prefix(mut path: ast::Path) -> Option<ast::Path> {
         for node in path.syntax().ancestors().skip(1) {
             match_ast! {
                 match node {
                     ast::UseTree(it) => if let Some(tree_path) = it.path() {
                         // Even a top-level path exists within a `UseTree` so we must explicitly
                         // allow our path but disallow anything else
                         if tree_path != path {
                             return Some(tree_path);
                         }
                     },
                     ast::UseTreeList(_it) => continue,
                     ast::Path(parent) => path = parent,
                     _ => return None,
                 }
             };
         }
         None
     }

     fn all_supers(path: &ast::Path) -> bool {
         let segment = match path.segment() {
             Some(it) => it,
             None => return false,
         };

         if segment.kind() != Some(PathSegmentKind::SuperKw) {
             return false;
         }

         if let Some(ref subpath) = path.qualifier() {
             return all_supers(subpath);
         }

         true
     }
 }

 fn validate_trait_object_ref_ty(ty: ast::RefType, errors: &mut Vec<SyntaxError>) {
     if let Some(ast::Type::DynTraitType(ty)) = ty.ty() {
         if let Some(err) = validate_trait_object_ty(ty) {
             errors.push(err);
         }
     }
 }

 fn validate_trait_object_ptr_ty(ty: ast::PtrType, errors: &mut Vec<SyntaxError>) {
     if let Some(ast::Type::DynTraitType(ty)) = ty.ty() {
         if let Some(err) = validate_trait_object_ty(ty) {
             errors.push(err);
         }
     }
 }

 fn validate_trait_object_fn_ptr_ret_ty(ty: ast::FnPtrType, errors: &mut Vec<SyntaxError>) {
     if let Some(ast::Type::DynTraitType(ty)) = ty.ret_type().and_then(|ty| ty.ty()) {
         if let Some(err) = validate_trait_object_ty(ty) {
             errors.push(err);
         }
     }
 }

 fn validate_trait_object_ty(ty: ast::DynTraitType) -> Option<SyntaxError> {
     let tbl = ty.type_bound_list()?;

     if tbl.bounds().count() > 1 {
         let dyn_token = ty.dyn_token()?;
         let potential_parenthesis =
             algo::skip_trivia_token(dyn_token.prev_token()?, Direction::Prev)?;
         let kind = potential_parenthesis.kind();
         if !matches!(kind, T!['('] | T![<] | T![=]) {
             return Some(SyntaxError::new("ambiguous `+` in a type", ty.syntax().text_range()));
         }
     }
     None
 }

 fn validate_macro_rules(mac: ast::MacroRules, errors: &mut Vec<SyntaxError>) {
     if let Some(vis) = mac.visibility() {
         errors.push(SyntaxError::new(
             "visibilities are not allowed on `macro_rules!` items",
             vis.syntax().text_range(),
         ));
     }
 }

 fn validate_const(const_: ast::Const, errors: &mut Vec<SyntaxError>) {
     if let Some(mut_token) = const_
         .const_token()
         .and_then(|t| t.next_token())
         .and_then(|t| algo::skip_trivia_token(t, Direction::Next))
         .filter(|t| t.kind() == T![mut])
     {
         errors.push(SyntaxError::new("const globals cannot be mutable", mut_token.text_range()));
     }
 }
	//! This module implements syntax validation that the parser doesn't handle.
	//!
	//! A failed validation emits a diagnostic.

	mod block;

	use crate::{
	algo,
	ast::{self, VisibilityOwner},
	match_ast, AstNode, SyntaxError,
	SyntaxKind::{CONST, FN, INT_NUMBER, TYPE_ALIAS},
	SyntaxNode, SyntaxToken, TextSize, T,
	};
	use rowan::Direction;
	use rustc_lexer::unescape::{
	self, unescape_byte, unescape_byte_literal, unescape_char, unescape_literal, Mode,
	};
	use std::convert::TryFrom;

	fn rustc_unescape_error_to_string(err: unescape::EscapeError) -> &'static str {
	use unescape::EscapeError as EE;

	#[rustfmt::skip]
	let err_message = match err {
	EE::ZeroChars => {
	"Literal must not be empty"
	}
	EE::MoreThanOneChar => {
	"Literal must be one character long"
	}
	EE::LoneSlash => {
	"Character must be escaped: `\\`"
	}
	EE::InvalidEscape => {
	"Invalid escape"
	}
	EE::BareCarriageReturn \| EE::BareCarriageReturnInRawString => {
	"Character must be escaped: `\r`"
	}
	EE::EscapeOnlyChar => {
	"Escape character `\\` must be escaped itself"
	}
	EE::TooShortHexEscape => {
	"ASCII hex escape code must have exactly two digits"
	}
	EE::InvalidCharInHexEscape => {
	"ASCII hex escape code must contain only hex characters"
	}
	EE::OutOfRangeHexEscape => {
	"ASCII hex escape code must be at most 0x7F"
	}
	EE::NoBraceInUnicodeEscape => {
	"Missing `{` to begin the unicode escape"
	}
	EE::InvalidCharInUnicodeEscape => {
	"Unicode escape must contain only hex characters and underscores"
	}
	EE::EmptyUnicodeEscape => {
	"Unicode escape must not be empty"
	}
	EE::UnclosedUnicodeEscape => {
	"Missing `}` to terminate the unicode escape"
	}
	EE::LeadingUnderscoreUnicodeEscape => {
	"Unicode escape code must not begin with an underscore"
	}
	EE::OverlongUnicodeEscape => {
	"Unicode escape code must have at most 6 digits"
	}
	EE::LoneSurrogateUnicodeEscape => {
	"Unicode escape code must not be a surrogate"
	}
	EE::OutOfRangeUnicodeEscape => {
	"Unicode escape code must be at most 0x10FFFF"
	}
	EE::UnicodeEscapeInByte => {
	"Byte literals must not contain unicode escapes"
	}
	EE::NonAsciiCharInByte \| EE::NonAsciiCharInByteString => {
	"Byte literals must not contain non-ASCII characters"
	}
	};

	err_message
	}

	pub(crate) fn validate(root: &SyntaxNode) -> Vec<SyntaxError> {
	// FIXME:
	// * Add unescape validation of raw string literals and raw byte string literals
	// * Add validation of doc comments are being attached to nodes

	let mut errors = Vec::new();
	for node in root.descendants() {
	match_ast! {
	match node {
	ast::Literal(it) => validate_literal(it, &mut errors),
	ast::Const(it) => validate_const(it, &mut errors),
	ast::BlockExpr(it) => block::validate_block_expr(it, &mut errors),
	ast::FieldExpr(it) => validate_numeric_name(it.name_ref(), &mut errors),
	ast::RecordExprField(it) => validate_numeric_name(it.name_ref(), &mut errors),
	ast::Visibility(it) => validate_visibility(it, &mut errors),
	ast::RangeExpr(it) => validate_range_expr(it, &mut errors),
	ast::PathSegment(it) => validate_path_keywords(it, &mut errors),
	ast::RefType(it) => validate_trait_object_ref_ty(it, &mut errors),
	ast::PtrType(it) => validate_trait_object_ptr_ty(it, &mut errors),
	ast::FnPtrType(it) => validate_trait_object_fn_ptr_ret_ty(it, &mut errors),
	ast::MacroRules(it) => validate_macro_rules(it, &mut errors),
	_ => (),
	}
	}
	}
	errors
	}

	fn validate_literal(literal: ast::Literal, acc: &mut Vec<SyntaxError>) {
	// FIXME: move this function to outer scope (https://github.com/rust-analyzer/rust-analyzer/pull/2834#discussion_r366196658)
	fn unquote(text: &str, prefix_len: usize, end_delimiter: char) -> Option<&str> {
	text.rfind(end_delimiter).and_then(\|end\| text.get(prefix_len..end))
	}

	let token = literal.token();
	let text = token.text();

	// FIXME: lift this lambda refactor to `fn` (https://github.com/rust-analyzer/rust-analyzer/pull/2834#discussion_r366199205)
	let mut push_err = \|prefix_len, (off, err): (usize, unescape::EscapeError)\| {
	let off = token.text_range().start() + TextSize::try_from(off + prefix_len).unwrap();
	acc.push(SyntaxError::new_at_offset(rustc_unescape_error_to_string(err), off));
	};

	match literal.kind() {
	ast::LiteralKind::String(s) => {
	if !s.is_raw() {
	if let Some(without_quotes) = unquote(text, 1, '"') {
	unescape_literal(without_quotes, Mode::Str, &mut \|range, char\| {
	if let Err(err) = char {
	push_err(1, (range.start, err));
	}
	})
	}
	}
	}
	ast::LiteralKind::ByteString(s) => {
	if !s.is_raw() {
	if let Some(without_quotes) = unquote(text, 2, '"') {
	unescape_byte_literal(without_quotes, Mode::ByteStr, &mut \|range, char\| {
	if let Err(err) = char {
	push_err(2, (range.start, err));
	}
	})
	}
	}
	}
	ast::LiteralKind::Char => {
	if let Some(Err(e)) = unquote(text, 1, '\'').map(unescape_char) {
	push_err(1, e);
	}
	}
	ast::LiteralKind::Byte => {
	if let Some(Err(e)) = unquote(text, 2, '\'').map(unescape_byte) {
	push_err(2, e);
	}
	}
	ast::LiteralKind::IntNumber(_)
	\| ast::LiteralKind::FloatNumber(_)
	\| ast::LiteralKind::Bool(_) => {}
	}
	}

	pub(crate) fn validate_block_structure(root: &SyntaxNode) {
	let mut stack = Vec::new();
	for node in root.descendants() {
	match node.kind() {
	T!['{'] => stack.push(node),
	T!['}'] => {
	if let Some(pair) = stack.pop() {
	assert_eq!(
	node.parent(),
	pair.parent(),
	"\nunpaired curlys:\n{}\n{:#?}\n",
	root.text(),
	root,
	);
	assert!(
	node.next_sibling().is_none() && pair.prev_sibling().is_none(),
	"\nfloating curlys at {:?}\nfile:\n{}\nerror:\n{}\n",
	node,
	root.text(),
	node.text(),
	);
	}
	}
	_ => (),
	}
	}
	}

	fn validate_numeric_name(name_ref: Option<ast::NameRef>, errors: &mut Vec<SyntaxError>) {
	if let Some(int_token) = int_token(name_ref) {
	if int_token.text().chars().any(\|c\| !c.is_digit(10)) {
	errors.push(SyntaxError::new(
	"Tuple (struct) field access is only allowed through \
	decimal integers with no underscores or suffix",
	int_token.text_range(),
	));
	}
	}

	fn int_token(name_ref: Option<ast::NameRef>) -> Option<SyntaxToken> {
	name_ref?.syntax().first_child_or_token()?.into_token().filter(\|it\| it.kind() == INT_NUMBER)
	}
	}

	fn validate_visibility(vis: ast::Visibility, errors: &mut Vec<SyntaxError>) {
	let parent = match vis.syntax().parent() {
	Some(it) => it,
	None => return,
	};
	match parent.kind() {
	FN \| CONST \| TYPE_ALIAS => (),
	_ => return,
	}

	let impl_def = match parent.parent().and_then(\|it\| it.parent()).and_then(ast::Impl::cast) {
	Some(it) => it,
	None => return,
	};
	if impl_def.trait_().is_some() {
	errors.push(SyntaxError::new("Unnecessary visibility qualifier", vis.syntax.text_range()));
	}
	}

	fn validate_range_expr(expr: ast::RangeExpr, errors: &mut Vec<SyntaxError>) {
	if expr.op_kind() == Some(ast::RangeOp::Inclusive) && expr.end().is_none() {
	errors.push(SyntaxError::new(
	"An inclusive range must have an end expression",
	expr.syntax().text_range(),
	));
	}
	}

	fn validate_path_keywords(segment: ast::PathSegment, errors: &mut Vec<SyntaxError>) {
	use ast::PathSegmentKind;

	let path = segment.parent_path();
	let is_path_start = segment.coloncolon_token().is_none() && path.qualifier().is_none();

	if let Some(token) = segment.self_token() {
	if !is_path_start {
	errors.push(SyntaxError::new(
	"The `self` keyword is only allowed as the first segment of a path",
	token.text_range(),
	));
	}
	} else if let Some(token) = segment.crate_token() {
	if !is_path_start \|\| use_prefix(path).is_some() {
	errors.push(SyntaxError::new(
	"The `crate` keyword is only allowed as the first segment of a path",
	token.text_range(),
	));
	}
	} else if let Some(token) = segment.super_token() {
	if segment.coloncolon_token().is_some() \|\| !all_supers(&path) {
	errors.push(SyntaxError::new(
	"The `super` keyword may only be preceded by other `super`s",
	token.text_range(),
	));
	return;
	}

	let mut curr_path = path;
	while let Some(prefix) = use_prefix(curr_path) {
	if !all_supers(&prefix) {
	errors.push(SyntaxError::new(
	"The `super` keyword may only be preceded by other `super`s",
	token.text_range(),
	));
	return;
	}
	curr_path = prefix;
	}
	}

	fn use_prefix(mut path: ast::Path) -> Option<ast::Path> {
	for node in path.syntax().ancestors().skip(1) {
	match_ast! {
	match node {
	ast::UseTree(it) => if let Some(tree_path) = it.path() {
	// Even a top-level path exists within a `UseTree` so we must explicitly
	// allow our path but disallow anything else
	if tree_path != path {
	return Some(tree_path);
	}
	},
	ast::UseTreeList(_it) => continue,
	ast::Path(parent) => path = parent,
	_ => return None,
	}
	};
	}
	None
	}

	fn all_supers(path: &ast::Path) -> bool {
	let segment = match path.segment() {
	Some(it) => it,
	None => return false,
	};

	if segment.kind() != Some(PathSegmentKind::SuperKw) {
	return false;
	}

	if let Some(ref subpath) = path.qualifier() {
	return all_supers(subpath);
	}

	true
	}
	}

	fn validate_trait_object_ref_ty(ty: ast::RefType, errors: &mut Vec<SyntaxError>) {
	if let Some(ast::Type::DynTraitType(ty)) = ty.ty() {
	if let Some(err) = validate_trait_object_ty(ty) {
	errors.push(err);
	}
	}
	}

	fn validate_trait_object_ptr_ty(ty: ast::PtrType, errors: &mut Vec<SyntaxError>) {
	if let Some(ast::Type::DynTraitType(ty)) = ty.ty() {
	if let Some(err) = validate_trait_object_ty(ty) {
	errors.push(err);
	}
	}
	}

	fn validate_trait_object_fn_ptr_ret_ty(ty: ast::FnPtrType, errors: &mut Vec<SyntaxError>) {
	if let Some(ast::Type::DynTraitType(ty)) = ty.ret_type().and_then(\|ty\| ty.ty()) {
	if let Some(err) = validate_trait_object_ty(ty) {
	errors.push(err);
	}
	}
	}

	fn validate_trait_object_ty(ty: ast::DynTraitType) -> Option<SyntaxError> {
	let tbl = ty.type_bound_list()?;

	if tbl.bounds().count() > 1 {
	let dyn_token = ty.dyn_token()?;
	let potential_parenthesis =
	algo::skip_trivia_token(dyn_token.prev_token()?, Direction::Prev)?;
	let kind = potential_parenthesis.kind();
	if !matches!(kind, T!['('] \| T![<] \| T![=]) {
	return Some(SyntaxError::new("ambiguous `+` in a type", ty.syntax().text_range()));
	}
	}
	None
	}

	fn validate_macro_rules(mac: ast::MacroRules, errors: &mut Vec<SyntaxError>) {
	if let Some(vis) = mac.visibility() {
	errors.push(SyntaxError::new(
	"visibilities are not allowed on `macro_rules!` items",
	vis.syntax().text_range(),
	));
	}
	}

	fn validate_const(const_: ast::Const, errors: &mut Vec<SyntaxError>) {
	if let Some(mut_token) = const_
	.const_token()
	.and_then(\|t\| t.next_token())
	.and_then(\|t\| algo::skip_trivia_token(t, Direction::Next))
	.filter(\|t\| t.kind() == T![mut])
	{
	errors.push(SyntaxError::new("const globals cannot be mutable", mut_token.text_range()));
	}
	}