SwiftLint/Source/SwiftLintFramework/Protocols/SwiftSyntaxRule.swift

import SwiftSyntax

/// A SwiftLint Rule backed by SwiftSyntax that does not use SourceKit requests.
public protocol SwiftSyntaxRule: SourceKitFreeRule {
    /// Produce a `ViolationsSyntaxVisitor` for the given file.
    ///
    /// - parameter file: The file for which to produce the visitor.
    ///
    /// - returns: A `ViolationsSyntaxVisitor` for the given file.
    func makeVisitor(file: SwiftLintFile) -> ViolationsSyntaxVisitor

    /// Produce a violation for the given file and absolute position.
    ///
    /// - parameter file:      The file for which to produce the violation.
    /// - parameter violation: A violation in the file.
    ///
    /// - returns: A violation for the given file and absolute position.
    func makeViolation(file: SwiftLintFile, violation: ReasonedRuleViolation) -> StyleViolation

    /// Gives a chance for the rule to do some pre-processing on the syntax tree.
    /// One typical example is using `SwiftOperators` to "fold" the tree, resolving operators precedence.
    /// By default, it just returns the same `syntaxTree`.
    ///
    /// - parameter syntaxTree: The syntax tree to run pre-processing on
    ///
    /// - returns: The tree that will be used to check for violations. If `nil`, this rule will return no violations.
    func preprocess(syntaxTree: SourceFileSyntax) -> SourceFileSyntax?
}

public extension SwiftSyntaxRule where Self: ConfigurationProviderRule,
                                       ConfigurationType: SeverityBasedRuleConfiguration {
    func makeViolation(file: SwiftLintFile, violation: ReasonedRuleViolation) -> StyleViolation {
        StyleViolation(
            ruleDescription: Self.description,
            severity: violation.severity ?? configuration.severity,
            location: Location(file: file, position: violation.position),
            reason: violation.reason
        )
    }
}

public extension SwiftSyntaxRule {
    /// Returns the source ranges in the specified file where this rule is disabled.
    ///
    /// - parameter file: The file to get regions.
    ///
    /// - returns: The source ranges in the specified file where this rule is disabled.
    func disabledRegions(file: SwiftLintFile) -> [SourceRange] {
        let locationConverter = file.locationConverter
        return file.regions()
            .filter { $0.isRuleDisabled(self) }
            .compactMap { $0.toSourceRange(locationConverter: locationConverter) }
    }

    func validate(file: SwiftLintFile) -> [StyleViolation] {
        guard let syntaxTree = preprocess(syntaxTree: file.syntaxTree) else {
            return []
        }

        return makeVisitor(file: file)
            .walk(tree: syntaxTree, handler: \.violations)
            .sorted()
            .map { makeViolation(file: file, violation: $0) }
    }

    func makeViolation(file: SwiftLintFile, violation: ReasonedRuleViolation) -> StyleViolation {
        guard let severity = violation.severity else {
            // This error will only be thrown in tests. It cannot come up at runtime.
            queuedFatalError("""
                A severity must be provided. Either define it in the violation or make the rule configuration \
                conform to `SeverityBasedRuleConfiguration` to take the default.
                """)
        }
        return StyleViolation(
            ruleDescription: Self.description,
            severity: severity,
            location: Location(file: file, position: violation.position),
            reason: violation.reason
        )
    }

    func preprocess(syntaxTree: SourceFileSyntax) -> SourceFileSyntax? {
        syntaxTree
    }
}

/// A violation produced by `ViolationsSyntaxVisitor`s.
public struct ReasonedRuleViolation: Comparable {
    /// The violation's position.
    public let position: AbsolutePosition
    /// A specific reason for the violation.
    public let reason: String?
    /// The violation's severity.
    public let severity: ViolationSeverity?

    /// Creates a `ReasonedRuleViolation`.
    ///
    /// - parameter position: The violations position in the analyzed source file.
    /// - parameter reason: The reason for the violation if different from the rule's description.
    /// - parameter severity: The severity of the violation if different from the rule's default configured severity.
    public init(position: AbsolutePosition, reason: String? = nil, severity: ViolationSeverity? = nil) {
        self.position = position
        self.reason = reason
        self.severity = severity
    }

    public static func < (lhs: Self, rhs: Self) -> Bool {
        lhs.position < rhs.position
    }
}

/// Extension for arrays of `ReasonedRuleViolation`s that provides the automatic conversion of
/// `AbsolutePosition`s into `ReasonedRuleViolation`s (without a specific reason).
extension Array where Element == ReasonedRuleViolation {
    /// Append a minimal violation for the specified position.
    ///
    /// - parameter position: The position for the violation to append.
    mutating func append(_ position: AbsolutePosition) {
        append(ReasonedRuleViolation(position: position))
    }

    /// Append minimal violations for the specified positions.
    ///
    /// - parameter positions: The positions for the violations to append.
    mutating func append(contentsOf positions: [AbsolutePosition]) {
        append(contentsOf: positions.map { ReasonedRuleViolation(position: $0) })
    }
}

/// A SwiftSyntax `SyntaxVisitor` that produces absolute positions where violations should be reported.
open class ViolationsSyntaxVisitor: SyntaxVisitor {
    /// Positions in a source file where violations should be reported.
    internal var violations: [ReasonedRuleViolation] = []
    /// List of declaration types that shall be skipped while traversing the AST.
    internal var skippableDeclarations: [DeclSyntaxProtocol.Type] { [] }

    override open func visit(_ node: ActorDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == ActorDeclSyntax.self } ? .skipChildren : .visitChildren
    }

    override open func visit(_ node: ClassDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == ClassDeclSyntax.self } ? .skipChildren : .visitChildren
    }

    override open func visit(_ node: EnumDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == EnumDeclSyntax.self } ? .skipChildren : .visitChildren
    }

    override open func visit(_ node: ExtensionDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == ExtensionDeclSyntax.self } ? .skipChildren : .visitChildren
    }

    override open func visit(_ node: FunctionDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == FunctionDeclSyntax.self } ? .skipChildren : .visitChildren
    }

    override open func visit(_ node: SubscriptDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == FunctionDeclSyntax.self } ? .skipChildren : .visitChildren
    }

    override open func visit(_ node: VariableDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == VariableDeclSyntax.self } ? .skipChildren : .visitChildren
    }

    override open func visit(_ node: ProtocolDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == ProtocolDeclSyntax.self } ? .skipChildren : .visitChildren
    }

    override open func visit(_ node: StructDeclSyntax) -> SyntaxVisitorContinueKind {
        skippableDeclarations.contains { $0 == StructDeclSyntax.self } ? .skipChildren : .visitChildren
    }
}

extension Array where Element == DeclSyntaxProtocol.Type {
    /// All visitable declaration syntax types.
    static let all: Self = [
        ActorDeclSyntax.self,
        ClassDeclSyntax.self,
        EnumDeclSyntax.self,
        FunctionDeclSyntax.self,
        ExtensionDeclSyntax.self,
        ProtocolDeclSyntax.self,
        StructDeclSyntax.self,
        VariableDeclSyntax.self
    ]

    /// Useful for class-specific checks since extensions and protocols do not allow nested classes.
    static let extensionsAndProtocols: Self = [
        ExtensionDeclSyntax.self,
        ProtocolDeclSyntax.self
    ]

    /// All declarations except for the specified ones.
    ///
    /// - parameter declarations: The declarations to exclude from all declarations.
    ///
    /// - returns: All declarations except for the specified ones.
    static func allExcept(_ declarations: Element...) -> Self {
        all.filter { decl in !declarations.contains { $0 == decl } }
    }
}