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Fix try/await expressions in NoAssignmentInExpressions. #533

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May 26, 2023
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29 changes: 27 additions & 2 deletions Sources/SwiftFormatRules/NoAssignmentInExpressions.swift
Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,7 @@ public final class NoAssignmentInExpressions: SyntaxFormatRule {
public override func visit(_ node: InfixOperatorExprSyntax) -> ExprSyntax {
// Diagnose any assignment that isn't directly a child of a `CodeBlockItem` (which would be the
// case if it was its own statement).
if isAssignmentExpression(node) && node.parent?.is(CodeBlockItemSyntax.self) == false {
if isAssignmentExpression(node) && !isStandaloneAssignmentStatement(node) {
diagnose(.moveAssignmentToOwnStatement, on: node)
}
return ExprSyntax(node)
Expand Down Expand Up @@ -59,7 +59,8 @@ public final class NoAssignmentInExpressions: SyntaxFormatRule {
item: .expr(ExprSyntax(assignmentExpr)),
semicolon: nil
)
.with(\.leadingTrivia,
.with(
\.leadingTrivia,
(returnStmt.leadingTrivia) + (assignmentExpr.leadingTrivia))
.with(\.trailingTrivia, []))
newItems.append(
Expand Down Expand Up @@ -106,6 +107,30 @@ public final class NoAssignmentInExpressions: SyntaxFormatRule {
return context.operatorTable.infixOperator(named: binaryOp.operatorToken.text)?.precedenceGroup
== "AssignmentPrecedence"
}

/// Returns a value indicating whether the given node is a standalone assignment statement.
///
/// This function considers try/await expressions and automatically walks up through them as
/// needed. This is because `try f().x = y` should still be a standalone assignment for our
/// purposes, even though a `TryExpr` will wrap the `InfixOperatorExpr` and thus would not be
/// considered a standalone assignment if we only checked the infix expression for a
/// `CodeBlockItem` parent.
private func isStandaloneAssignmentStatement(_ node: InfixOperatorExprSyntax) -> Bool {
var node = Syntax(node)
while
let parent = node.parent,
parent.is(TryExprSyntax.self) || parent.is(AwaitExprSyntax.self)
{
node = parent
}

guard let parent = node.parent else {
// This shouldn't happen under normal circumstances (i.e., unless the expression is detached
// from the rest of a tree). In that case, we may as well consider it to be "standalone".
return true
}
return parent.is(CodeBlockItemSyntax.self)
}
}

extension Finding.Message {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -161,4 +161,23 @@ final class NoAssignmentInExpressionsTests: LintOrFormatRuleTestCase {
)
XCTAssertDiagnosed(.moveAssignmentToOwnStatement, line: 2, column: 29)
}

func testTryAndAwaitAssignmentExpressionsAreUnchanged() {
XCTAssertFormatting(
NoAssignmentInExpressions.self,
input: """
func foo() {
try a.b = c
await a.b = c
}
""",
expected: """
func foo() {
try a.b = c
await a.b = c
}
"""
)
XCTAssertNotDiagnosed(.moveAssignmentToOwnStatement)
}
}