SwiftLint/Source/SwiftLintBuiltInRules/Rules/Idiomatic/LegacyConstantRule.swift

import SwiftSyntax
import SwiftSyntaxBuilder

@SwiftSyntaxRule(explicitRewriter: true)
struct LegacyConstantRule: Rule {
    var configuration = SeverityConfiguration<Self>(.warning)

    static let description = RuleDescription(
        identifier: "legacy_constant",
        name: "Legacy Constant",
        description: "Struct-scoped constants are preferred over legacy global constants",
        kind: .idiomatic,
        nonTriggeringExamples: LegacyConstantRuleExamples.nonTriggeringExamples,
        triggeringExamples: LegacyConstantRuleExamples.triggeringExamples,
        corrections: LegacyConstantRuleExamples.corrections
    )
}

private extension LegacyConstantRule {
    final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
        override func visitPost(_ node: DeclReferenceExprSyntax) {
            if LegacyConstantRuleExamples.patterns.keys.contains(node.baseName.text) {
                violations.append(node.positionAfterSkippingLeadingTrivia)
            }
        }

        override func visitPost(_ node: FunctionCallExprSyntax) {
            if node.isLegacyPiExpression {
                violations.append(node.positionAfterSkippingLeadingTrivia)
            }
        }
    }

    final class Rewriter: ViolationsSyntaxRewriter<ConfigurationType> {
        override func visit(_ node: DeclReferenceExprSyntax) -> ExprSyntax {
            guard let correction = LegacyConstantRuleExamples.patterns[node.baseName.text] else {
                return super.visit(node)
            }
            numberOfCorrections += 1
            return ("\(raw: correction)" as ExprSyntax)
                .with(\.leadingTrivia, node.leadingTrivia)
                .with(\.trailingTrivia, node.trailingTrivia)
        }

        override func visit(_ node: FunctionCallExprSyntax) -> ExprSyntax {
            guard node.isLegacyPiExpression,
                  let calledExpression = node.calledExpression.as(DeclReferenceExprSyntax.self) else {
                return super.visit(node)
            }
            numberOfCorrections += 1
            return ("\(raw: calledExpression.baseName.text).pi" as ExprSyntax)
                .with(\.leadingTrivia, node.leadingTrivia)
                .with(\.trailingTrivia, node.trailingTrivia)
        }
    }
}

private extension FunctionCallExprSyntax {
    var isLegacyPiExpression: Bool {
        guard
            let calledExpression = calledExpression.as(DeclReferenceExprSyntax.self),
            calledExpression.baseName.text == "CGFloat" || calledExpression.baseName.text == "Float",
            let argument = arguments.onlyElement?.expression.as(DeclReferenceExprSyntax.self),
            argument.baseName.text == "M_PI"
        else {
            return false
        }

        return true
    }
}