public static bool CanRemoveParentheses(
this ParenthesizedExpressionSyntax node, SemanticModel semanticModel, CancellationToken cancellationToken)
{
if (node.OpenParenToken.IsMissing || node.CloseParenToken.IsMissing)
{
// int x = (3;
return(false);
}
var nodeParent = node.Parent;
if (nodeParent == null)
{
return(false);
}
var expression = node.Expression;
// The 'direct' expression that contains this parenthesized node. Note: in the case
// of code like: ```x is (y)``` there is an intermediary 'no-syntax' 'ConstantPattern'
// node between the 'is-pattern' node and the parenthesized expression. So we manually
// jump past that as, for all intents and purposes, we want to consider the 'is' expression
// as the parent expression of the (y) expression.
var parentExpression = nodeParent.IsKind(SyntaxKind.ConstantPattern)
? nodeParent.Parent as ExpressionSyntax
: nodeParent as ExpressionSyntax;
// Have to be careful if we would remove parens and cause a + and a + to become a ++.
// (same with - as well).
var tokenBeforeParen = node.GetFirstToken().GetPreviousToken();
var tokenAfterParen = node.Expression.GetFirstToken();
var previousChar = tokenBeforeParen.Text.LastOrDefault();
var nextChar = tokenAfterParen.Text.FirstOrDefault();
if ((previousChar == '+' && nextChar == '+') ||
(previousChar == '-' && nextChar == '-'))
{
return(false);
}
// Simplest cases:
// ((x)) -> (x)
if (expression.IsKind(SyntaxKind.ParenthesizedExpression) ||
parentExpression.IsKind(SyntaxKind.ParenthesizedExpression))
{
return(true);
}
if (expression is StackAllocArrayCreationExpressionSyntax or ImplicitStackAllocArrayCreationExpressionSyntax)
{
// var span = (stackalloc byte[8]);
// https://github.com/dotnet/roslyn/issues/44629
// The code semantics changes if the parenthesis removed.
// With parenthesis: variable span is of type `Span<byte>`.
// Without parenthesis: variable span is of type `byte*` which can only be used in unsafe context.
if (nodeParent is EqualsValueClauseSyntax {
Parent : VariableDeclaratorSyntax {
Parent : VariableDeclarationSyntax varDecl
}
})
public static bool CanRemoveParentheses(this ParenthesizedExpressionSyntax node, SemanticModel semanticModel)
{
if (node.OpenParenToken.IsMissing || node.CloseParenToken.IsMissing)
{
// int x = (3;
return(false);
}
var expression = node.Expression;
// The 'direct' expression that contains this parenthesized node. Note: in the case
// of code like: ```x is (y)``` there is an intermediary 'no-syntax' 'ConstantPattern'
// node between the 'is-pattern' node and the parenthesized expression. So we manually
// jump past that as, for all intents and purposes, we want to consider the 'is' expression
// as the parent expression of the (y) expression.
var parentExpression = node.IsParentKind(SyntaxKind.ConstantPattern)
? node.Parent.Parent as ExpressionSyntax
: node.Parent as ExpressionSyntax;
// Have to be careful if we would remove parens and cause a + and a + to become a ++.
// (same with - as well).
var tokenBeforeParen = node.GetFirstToken().GetPreviousToken();
var tokenAfterParen = node.Expression.GetFirstToken();
var previousChar = tokenBeforeParen.Text.LastOrDefault();
var nextChar = tokenAfterParen.Text.FirstOrDefault();
if ((previousChar == '+' && nextChar == '+') ||
(previousChar == '-' && nextChar == '-'))
{
return(false);
}
// Simplest cases:
// ((x)) -> (x)
if (expression.IsKind(SyntaxKind.ParenthesizedExpression) ||
parentExpression.IsKind(SyntaxKind.ParenthesizedExpression))
{
return(true);
}
// (x); -> x;
if (node.IsParentKind(SyntaxKind.ExpressionStatement))
{
return(true);
}
// => (x) -> => x
if (node.IsParentKind(SyntaxKind.ArrowExpressionClause))
{
return(true);
}
// checked((x)) -> checked(x)
if (node.IsParentKind(SyntaxKind.CheckedExpression) ||
node.IsParentKind(SyntaxKind.UncheckedExpression))
{
return(true);
}
// ((x, y)) -> (x, y)
if (expression.IsKind(SyntaxKind.TupleExpression))
{
return(true);
}
// int Prop => (x); -> int Prop => x;
if (node.Parent is ArrowExpressionClauseSyntax arrowExpressionClause && arrowExpressionClause.Expression == node)
{
return(true);
}
// Don't change (x?.Count).GetValueOrDefault() to x?.Count.GetValueOrDefault()
if (expression.IsKind(SyntaxKind.ConditionalAccessExpression) && parentExpression is MemberAccessExpressionSyntax)
{
return(false);
}
// Easy statement-level cases:
// var y = (x); -> var y = x;
// var (y, z) = (x); -> var (y, z) = x;
// if ((x)) -> if (x)
// return (x); -> return x;
// yield return (x); -> yield return x;
// throw (x); -> throw x;
// switch ((x)) -> switch (x)
// while ((x)) -> while (x)
// do { } while ((x)) -> do { } while (x)
// for(;(x);) -> for(;x;)
// foreach (var y in (x)) -> foreach (var y in x)
// lock ((x)) -> lock (x)
// using ((x)) -> using (x)
// catch when ((x)) -> catch when (x)
if ((node.IsParentKind(SyntaxKind.EqualsValueClause) && ((EqualsValueClauseSyntax)node.Parent).Value == node) ||
(node.IsParentKind(SyntaxKind.IfStatement) && ((IfStatementSyntax)node.Parent).Condition == node) ||
(node.IsParentKind(SyntaxKind.ReturnStatement) && ((ReturnStatementSyntax)node.Parent).Expression == node) ||
(node.IsParentKind(SyntaxKind.YieldReturnStatement) && ((YieldStatementSyntax)node.Parent).Expression == node) ||
(node.IsParentKind(SyntaxKind.ThrowStatement) && ((ThrowStatementSyntax)node.Parent).Expression == node) ||
(node.IsParentKind(SyntaxKind.SwitchStatement) && ((SwitchStatementSyntax)node.Parent).Expression == node) ||
(node.IsParentKind(SyntaxKind.WhileStatement) && ((WhileStatementSyntax)node.Parent).Condition == node) ||
(node.IsParentKind(SyntaxKind.DoStatement) && ((DoStatementSyntax)node.Parent).Condition == node) ||
(node.IsParentKind(SyntaxKind.ForStatement) && ((ForStatementSyntax)node.Parent).Condition == node) ||
(node.IsParentKind(SyntaxKind.ForEachStatement, SyntaxKind.ForEachVariableStatement) && ((CommonForEachStatementSyntax)node.Parent).Expression == node) ||
(node.IsParentKind(SyntaxKind.LockStatement) && ((LockStatementSyntax)node.Parent).Expression == node) ||
(node.IsParentKind(SyntaxKind.UsingStatement) && ((UsingStatementSyntax)node.Parent).Expression == node) ||
(node.IsParentKind(SyntaxKind.CatchFilterClause) && ((CatchFilterClauseSyntax)node.Parent).FilterExpression == node))
{
return(true);
}
// Handle expression-level ambiguities
if (RemovalMayIntroduceCastAmbiguity(node) ||
RemovalMayIntroduceCommaListAmbiguity(node) ||
RemovalMayIntroduceInterpolationAmbiguity(node))
{
return(false);
}
// Cases:
// (C)(this) -> (C)this
if (node.IsParentKind(SyntaxKind.CastExpression) && expression.IsKind(SyntaxKind.ThisExpression))
{
return(true);
}
// Cases:
// y((x)) -> y(x)
if (node.IsParentKind(SyntaxKind.Argument) && ((ArgumentSyntax)node.Parent).Expression == node)
{
return(true);
}
// Cases:
// $"{(x)}" -> $"{x}"
if (node.IsParentKind(SyntaxKind.Interpolation))
{
return(true);
}
// Cases:
// ($"{x}") -> $"{x}"
if (expression.IsKind(SyntaxKind.InterpolatedStringExpression))
{
return(true);
}
// Cases:
// {(x)} -> {x}
if (node.Parent is InitializerExpressionSyntax)
{
// Assignment expressions are not allowed in initializers
if (expression.IsAnyAssignExpression())
{
return(false);
}
return(true);
}
// Cases:
// new {(x)} -> {x}
// new { a = (x)} -> { a = x }
// new { a = (x = c)} -> { a = x = c }
if (node.Parent is AnonymousObjectMemberDeclaratorSyntax anonymousDeclarator)
{
// Assignment expressions are not allowed unless member is named
if (anonymousDeclarator.NameEquals == null && expression.IsAnyAssignExpression())
{
return(false);
}
return(true);
}
// Cases:
// where (x + 1 > 14) -> where x + 1 > 14
if (node.Parent is QueryClauseSyntax)
{
return(true);
}
// Cases:
// (x) -> x
// (x.y) -> x.y
if (IsSimpleOrDottedName(expression))
{
return(true);
}
// Cases:
// ('') -> ''
// ("") -> ""
// (false) -> false
// (true) -> true
// (null) -> null
// (1) -> 1
if (expression.IsAnyLiteralExpression())
{
return(true);
}
// x ?? (throw ...) -> x ?? throw ...
if (expression.IsKind(SyntaxKind.ThrowExpression) &&
node.IsParentKind(SyntaxKind.CoalesceExpression) &&
((BinaryExpressionSyntax)node.Parent).Right == node)
{
return(true);
}
// case (x): -> case x:
if (node.IsParentKind(SyntaxKind.CaseSwitchLabel))
{
return(true);
}
// case (x) when y: -> case x when y:
if (node.IsParentKind(SyntaxKind.ConstantPattern) &&
node.Parent.IsParentKind(SyntaxKind.CasePatternSwitchLabel))
{
return(true);
}
// case x when (y): -> case x when y:
if (node.IsParentKind(SyntaxKind.WhenClause))
{
return(true);
}
// #if (x) -> #if x
if (node.Parent is DirectiveTriviaSyntax)
{
return(true);
}
// If we have: (X)(++x) or (X)(--x), we don't want to remove the parens. doing so can
// make the ++/-- now associate with the previous part of the cast expression.
if (parentExpression.IsKind(SyntaxKind.CastExpression))
{
if (expression.IsKind(SyntaxKind.PreIncrementExpression) ||
expression.IsKind(SyntaxKind.PreDecrementExpression))
{
return(false);
}
}
// (condition ? ref a : ref b ) = SomeValue, parenthesis can't be removed for when conditional expression appears at left
// This syntax is only allowed since C# 7.2
if (expression.IsKind(SyntaxKind.ConditionalExpression) &&
node.IsLeftSideOfAnyAssignExpression())
{
return(false);
}
// Operator precedence cases:
// - If the parent is not an expression, do not remove parentheses
// - Otherwise, parentheses may be removed if doing so does not change operator associations.
return(parentExpression != null && !RemovalChangesAssociation(node, parentExpression, semanticModel));
}
public static bool CanRemoveParentheses(
this ParenthesizedExpressionSyntax node, SemanticModel semanticModel, CancellationToken cancellationToken)
{
if (node.OpenParenToken.IsMissing || node.CloseParenToken.IsMissing)
{
// int x = (3;
return(false);
}
var expression = node.Expression;
// The 'direct' expression that contains this parenthesized node. Note: in the case
// of code like: ```x is (y)``` there is an intermediary 'no-syntax' 'ConstantPattern'
// node between the 'is-pattern' node and the parenthesized expression. So we manually
// jump past that as, for all intents and purposes, we want to consider the 'is' expression
// as the parent expression of the (y) expression.
var parentExpression = node.IsParentKind(SyntaxKind.ConstantPattern)
? node.Parent.Parent as ExpressionSyntax
: node.Parent as ExpressionSyntax;
// Have to be careful if we would remove parens and cause a + and a + to become a ++.
// (same with - as well).
var tokenBeforeParen = node.GetFirstToken().GetPreviousToken();
var tokenAfterParen = node.Expression.GetFirstToken();
var previousChar = tokenBeforeParen.Text.LastOrDefault();
var nextChar = tokenAfterParen.Text.FirstOrDefault();
if ((previousChar == '+' && nextChar == '+') ||
(previousChar == '-' && nextChar == '-'))
{
return(false);
}
// Simplest cases:
// ((x)) -> (x)
if (expression.IsKind(SyntaxKind.ParenthesizedExpression) ||
parentExpression.IsKind(SyntaxKind.ParenthesizedExpression))
{
return(true);
}
if (expression is StackAllocArrayCreationExpressionSyntax ||
expression is ImplicitStackAllocArrayCreationExpressionSyntax)
{
// var span = (stackalloc byte[8]);
// https://github.com/dotnet/roslyn/issues/44629
// The code semantics changes if the parenthesis removed.
// With parenthesis: variable span is of type `Span<byte>`.
// Without parenthesis: variable span is of type `byte*` which can only be used in unsafe context.
return(false);
}
// (throw ...) -> throw ...
if (expression.IsKind(SyntaxKind.ThrowExpression))
{
return(true);
}
// (x); -> x;
if (node.IsParentKind(SyntaxKind.ExpressionStatement))
{
return(true);
}
// => (x) -> => x
if (node.IsParentKind(SyntaxKind.ArrowExpressionClause))
{
return(true);
}
// checked((x)) -> checked(x)
if (node.IsParentKind(SyntaxKind.CheckedExpression) ||
node.IsParentKind(SyntaxKind.UncheckedExpression))
{
return(true);
}
// ((x, y)) -> (x, y)
if (expression.IsKind(SyntaxKind.TupleExpression))
{
return(true);
}
// int Prop => (x); -> int Prop => x;
if (node.Parent is ArrowExpressionClauseSyntax arrowExpressionClause && arrowExpressionClause.Expression == node)
{
return(true);
}
// Easy statement-level cases:
// var y = (x); -> var y = x;
// var (y, z) = (x); -> var (y, z) = x;
// if ((x)) -> if (x)
// return (x); -> return x;
// yield return (x); -> yield return x;
// throw (x); -> throw x;
// switch ((x)) -> switch (x)
// while ((x)) -> while (x)
// do { } while ((x)) -> do { } while (x)
// for(;(x);) -> for(;x;)
// foreach (var y in (x)) -> foreach (var y in x)
// lock ((x)) -> lock (x)
// using ((x)) -> using (x)
// catch when ((x)) -> catch when (x)
if ((node.IsParentKind(SyntaxKind.EqualsValueClause, out EqualsValueClauseSyntax equalsValue) && equalsValue.Value == node) ||
(node.IsParentKind(SyntaxKind.IfStatement, out IfStatementSyntax ifStatement) && ifStatement.Condition == node) ||
(node.IsParentKind(SyntaxKind.ReturnStatement, out ReturnStatementSyntax returnStatement) && returnStatement.Expression == node) ||
(node.IsParentKind(SyntaxKind.YieldReturnStatement, out YieldStatementSyntax yieldStatement) && yieldStatement.Expression == node) ||
(node.IsParentKind(SyntaxKind.ThrowStatement, out ThrowStatementSyntax throwStatement) && throwStatement.Expression == node) ||
(node.IsParentKind(SyntaxKind.SwitchStatement, out SwitchStatementSyntax switchStatement) && switchStatement.Expression == node) ||
(node.IsParentKind(SyntaxKind.WhileStatement, out WhileStatementSyntax whileStatement) && whileStatement.Condition == node) ||
(node.IsParentKind(SyntaxKind.DoStatement, out DoStatementSyntax doStatement) && doStatement.Condition == node) ||
(node.IsParentKind(SyntaxKind.ForStatement, out ForStatementSyntax forStatement) && forStatement.Condition == node) ||
(node.IsParentKind(SyntaxKind.ForEachStatement, SyntaxKind.ForEachVariableStatement) && ((CommonForEachStatementSyntax)node.Parent).Expression == node) ||
(node.IsParentKind(SyntaxKind.LockStatement, out LockStatementSyntax lockStatement) && lockStatement.Expression == node) ||
(node.IsParentKind(SyntaxKind.UsingStatement, out UsingStatementSyntax usingStatement) && usingStatement.Expression == node) ||
(node.IsParentKind(SyntaxKind.CatchFilterClause, out CatchFilterClauseSyntax catchFilter) && catchFilter.FilterExpression == node))
{
return(true);
}
// Handle expression-level ambiguities
if (RemovalMayIntroduceCastAmbiguity(node) ||
RemovalMayIntroduceCommaListAmbiguity(node) ||
RemovalMayIntroduceInterpolationAmbiguity(node) ||
RemovalWouldChangeConstantReferenceToTypeReference(node, expression, semanticModel, cancellationToken))
{
return(false);
}
// Cases:
// (C)(this) -> (C)this
if (node.IsParentKind(SyntaxKind.CastExpression) && expression.IsKind(SyntaxKind.ThisExpression))
{
return(true);
}
// Cases:
// y((x)) -> y(x)
if (node.IsParentKind(SyntaxKind.Argument, out ArgumentSyntax argument) && argument.Expression == node)
{
return(true);
}
// Cases:
// $"{(x)}" -> $"{x}"
if (node.IsParentKind(SyntaxKind.Interpolation))
{
return(true);
}
// Cases:
// ($"{x}") -> $"{x}"
if (expression.IsKind(SyntaxKind.InterpolatedStringExpression))
{
return(true);
}
// Cases:
// {(x)} -> {x}
if (node.Parent is InitializerExpressionSyntax)
{
// Assignment expressions are not allowed in initializers
if (expression.IsAnyAssignExpression())
{
return(false);
}
return(true);
}
// Cases:
// new {(x)} -> {x}
// new { a = (x)} -> { a = x }
// new { a = (x = c)} -> { a = x = c }
if (node.Parent is AnonymousObjectMemberDeclaratorSyntax anonymousDeclarator)
{
// Assignment expressions are not allowed unless member is named
if (anonymousDeclarator.NameEquals == null && expression.IsAnyAssignExpression())
{
return(false);
}
return(true);
}
// Cases:
// where (x + 1 > 14) -> where x + 1 > 14
if (node.Parent is QueryClauseSyntax)
{
return(true);
}
// Cases:
// (x) -> x
// (x.y) -> x.y
if (IsSimpleOrDottedName(expression))
{
return(true);
}
// Cases:
// ('') -> ''
// ("") -> ""
// (false) -> false
// (true) -> true
// (null) -> null
// (default) -> default;
// (1) -> 1
if (expression.IsAnyLiteralExpression())
{
return(true);
}
// (this) -> this
if (expression.IsKind(SyntaxKind.ThisExpression))
{
return(true);
}
// x ?? (throw ...) -> x ?? throw ...
if (expression.IsKind(SyntaxKind.ThrowExpression) &&
node.IsParentKind(SyntaxKind.CoalesceExpression, out BinaryExpressionSyntax binary) &&
binary.Right == node)
{
return(true);
}
// case (x): -> case x:
if (node.IsParentKind(SyntaxKind.CaseSwitchLabel))
{
return(true);
}
// case (x) when y: -> case x when y:
if (node.IsParentKind(SyntaxKind.ConstantPattern) &&
node.Parent.IsParentKind(SyntaxKind.CasePatternSwitchLabel))
{
return(true);
}
// case x when (y): -> case x when y:
if (node.IsParentKind(SyntaxKind.WhenClause))
{
return(true);
}
// #if (x) -> #if x
if (node.Parent is DirectiveTriviaSyntax)
{
return(true);
}
// Switch expression arm
// x => (y)
if (node.Parent is SwitchExpressionArmSyntax arm && arm.Expression == node)
{
return(true);
}
// If we have: (X)(++x) or (X)(--x), we don't want to remove the parens. doing so can
// make the ++/-- now associate with the previous part of the cast expression.
if (parentExpression.IsKind(SyntaxKind.CastExpression))
{
if (expression.IsKind(SyntaxKind.PreIncrementExpression) ||
expression.IsKind(SyntaxKind.PreDecrementExpression))
{
return(false);
}
}
// (condition ? ref a : ref b ) = SomeValue, parenthesis can't be removed for when conditional expression appears at left
// This syntax is only allowed since C# 7.2
if (expression.IsKind(SyntaxKind.ConditionalExpression) &&
node.IsLeftSideOfAnyAssignExpression())
{
return(false);
}
// Don't change (x?.Count)... to x?.Count...
//
// It very much changes the semantics to have code that always executed (outside the
// parenthesized expression) now only conditionally run depending on if 'x' is null or
// not.
if (expression.IsKind(SyntaxKind.ConditionalAccessExpression))
{
return(false);
}
// Operator precedence cases:
// - If the parent is not an expression, do not remove parentheses
// - Otherwise, parentheses may be removed if doing so does not change operator associations.
return(parentExpression != null && !RemovalChangesAssociation(node, parentExpression, semanticModel));
}