Integrate Swift Syntax in the force_cast rule (#3867)

We've tried adding Swift Syntax support to SwiftLint in the past but had to turn it off in #3107 due to distribution and portability issues.

With https://github.com/keith/StaticInternalSwiftSyntaxParser it should be possible to avoid those issues by statically linking the internal Swift syntax parser so it's available no matter where users have Xcode installed on their computer.

By removing all calls to SourceKit (collecting comment commands + checking the current Swift version), there's a really significant performance improvement.

| Framework | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| SourceKit | 517.8 ± 8.3 | 505.5 | 531.1 | 6.59 ± 0.43 |
| SwiftSyntax | 78.6 ± 5.0 | 72.6 | 92.1 | 1.00 |

In practice, the SourceKit overhead will continue being there for as long as any rule being run is still looking up the SwiftLint syntax map though.

CHANGELOG.md

@@ -13,7 +13,11 @@
 
 #### Experimental
 
-* None.
+* The `force_cast` rule has been updated to use SwiftSyntax to find violations
+  instead of SourceKit. Please report any problems you encounter by opening a
+  GitHub issue. If this is successful, more rules may use Swift Syntax in the
+  future.  
+  [JP Simard](https://github.com/jpsim)
 
 #### Enhancements
 

Makefile

@@ -6,21 +6,13 @@ XCODEFLAGS=-scheme 'swiftlint' \
 	DSTROOT=$(TEMPORARY_FOLDER) \
 	OTHER_LDFLAGS=-Wl,-headerpad_max_install_names
 
-SWIFT_BUILD_FLAGS=--configuration release
+SWIFT_BUILD_FLAGS=--configuration release -Xlinker -dead_strip
 UNAME=$(shell uname)
-ifeq ($(UNAME), Darwin)
-USE_SWIFT_STATIC_STDLIB:=$(shell test -d $$(dirname $$(xcrun --find swift))/../lib/swift_static/macosx && echo yes)
-ifeq ($(USE_SWIFT_STATIC_STDLIB), yes)
-SWIFT_BUILD_FLAGS+= -Xswiftc -static-stdlib
-endif
-# SwiftPM 5.3 uses the `XCBuild.framework` to generate a universal binary when it receives multiple `--arch` options.
-SWIFT_BUILD_ARCHS:= arm64 x86_64
-# If SwiftPM supports `--arch $(1)` and `swiftc` succeeds in building with `-target $(1)-apple-macos10.9`, then produce `--arch $(1)`.
-ARCH_OPTION=$(shell swift build --show-bin-path --arch $(1) &>/dev/null && echo ''|swiftc -target $(1)-apple-macos10.9 - -o /dev/null &>/dev/null && echo "--arch" $(1))
-SWIFT_BUILD_FLAGS+=$(foreach arch,$(SWIFT_BUILD_ARCHS),$(call ARCH_OPTION,$(arch)))
-endif # Darwin
 
-SWIFTLINT_EXECUTABLE=$(shell swift build $(SWIFT_BUILD_FLAGS) --show-bin-path)/swiftlint
+SWIFTLINT_EXECUTABLE_X86=$(shell swift build $(SWIFT_BUILD_FLAGS) --arch x86_64 --show-bin-path)/swiftlint
+SWIFTLINT_EXECUTABLE_ARM64=$(shell swift build $(SWIFT_BUILD_FLAGS) --arch arm64 --show-bin-path)/swiftlint
+SWIFTLINT_EXECUTABLE_PARENT=.build/universal
+SWIFTLINT_EXECUTABLE=$(SWIFTLINT_EXECUTABLE_PARENT)/swiftlint
 
 TSAN_LIB=$(subst bin/swift,lib/swift/clang/lib/darwin/libclang_rt.tsan_osx_dynamic.dylib,$(shell xcrun --find swift))
 TSAN_SWIFT_BUILD_FLAGS=-Xswiftc -sanitize=thread
@@ -74,8 +66,19 @@ clean:
 clean_xcode:
 	$(BUILD_TOOL) $(XCODEFLAGS) -configuration Test clean
 
-build:
-	swift build $(SWIFT_BUILD_FLAGS)
+build_x86_64:
+	swift build $(SWIFT_BUILD_FLAGS) --arch x86_64
+
+build_arm64:
+	swift build $(SWIFT_BUILD_FLAGS) --arch arm64
+
+build: clean build_x86_64 build_arm64
+	# Need to build for each arch independently to work around https://bugs.swift.org/browse/SR-15802
+	mkdir -p $(SWIFTLINT_EXECUTABLE_PARENT)
+	lipo -create -output \
+		"$(SWIFTLINT_EXECUTABLE)" \
+		"$(SWIFTLINT_EXECUTABLE_X86)" \
+		"$(SWIFTLINT_EXECUTABLE_ARM64)"
 
 build_with_disable_sandbox:
 	swift build --disable-sandbox $(SWIFT_BUILD_FLAGS)

Package.resolved

@@ -19,6 +19,15 @@
           "version": "1.0.3"
         }
       },
+      {
+        "package": "SwiftSyntax",
+        "repositoryURL": "https://github.com/apple/swift-syntax.git",
+        "state": {
+          "branch": null,
+          "revision": "cf40be70deaf4ce7d44eb1a7e14299c391e2363f",
+          "version": null
+        }
+      },
       {
         "package": "SwiftyTextTable",
         "repositoryURL": "https://github.com/scottrhoyt/SwiftyTextTable.git",

Package.swift

@@ -7,6 +7,12 @@ private let addCryptoSwift = false
 private let addCryptoSwift = true
 #endif
 
+#if os(macOS)
+private let staticSwiftSyntax = true
+#else
+private let staticSwiftSyntax = false
+#endif
+
 let package = Package(
     name: "SwiftLint",
     platforms: [.macOS(.v10_12)],
@@ -16,6 +22,8 @@ let package = Package(
     ],
     dependencies: [
         .package(name: "swift-argument-parser", url: "https://github.com/apple/swift-argument-parser.git", from: "1.0.1"),
+        .package(name: "SwiftSyntax", url: "https://github.com/apple/swift-syntax.git",
+                 .revision("cf40be70deaf4ce7d44eb1a7e14299c391e2363f")),
         .package(url: "https://github.com/jpsim/SourceKitten.git", from: "0.31.1"),
         .package(url: "https://github.com/jpsim/Yams.git", from: "4.0.2"),
         .package(url: "https://github.com/scottrhoyt/SwiftyTextTable.git", from: "0.9.0"),
@@ -33,8 +41,11 @@ let package = Package(
             name: "SwiftLintFramework",
             dependencies: [
                 .product(name: "SourceKittenFramework", package: "SourceKitten"),
+                "SwiftSyntax",
                 "Yams",
-            ] + (addCryptoSwift ? ["CryptoSwift"] : [])
+            ]
+            + (addCryptoSwift ? ["CryptoSwift"] : [])
+            + (staticSwiftSyntax ? ["lib_InternalSwiftSyntaxParser"] : [])
         ),
         .testTarget(
             name: "SwiftLintFrameworkTests",
@@ -44,6 +55,10 @@ let package = Package(
             exclude: [
                 "Resources",
             ]
-        )
-    ]
+        ),
+    ] + (staticSwiftSyntax ? [.binaryTarget(
+            name: "lib_InternalSwiftSyntaxParser",
+            url: "https://github.com/keith/StaticInternalSwiftSyntaxParser/releases/download/5.5.2/lib_InternalSwiftSyntaxParser.xcframework.zip",
+            checksum: "96bbc9ab4679953eac9ee46778b498cb559b8a7d9ecc658e54d6679acfbb34b8"
+        )] : [])
 )

Source/SwiftLintFramework/Rules/Idiomatic/ForceCastRule.swift

@@ -1,4 +1,13 @@
 import SourceKittenFramework
+import SwiftSyntax
+
+private let warnSyntaxParserFailureOnceImpl: Void = {
+    queuedPrintError("The force_cast rule is disabled because the Swift Syntax tree could not be parsed")
+}()
+
+private func warnSyntaxParserFailureOnce() {
+    _ = warnSyntaxParserFailureOnceImpl
+}
 
 public struct ForceCastRule: ConfigurationProviderRule, AutomaticTestableRule {
     public var configuration = SeverityConfiguration(.error)
@@ -17,10 +26,26 @@ public struct ForceCastRule: ConfigurationProviderRule, AutomaticTestableRule {
     )
 
     public func validate(file: SwiftLintFile) -> [StyleViolation] {
-        return file.match(pattern: "as!", with: [.keyword]).map {
+        guard let tree = try? SyntaxParser.parse(source: file.contents) else {
+            warnSyntaxParserFailureOnce()
+            return []
+        }
+        let visitor = ForceCastRuleVisitor()
+        visitor.walk(tree)
+        return visitor.positions.map { position in
             StyleViolation(ruleDescription: Self.description,
                            severity: configuration.severity,
-                           location: Location(file: file, characterOffset: $0.location))
+                           location: Location(file: file, byteOffset: ByteCount(position.utf8Offset)))
+        }
+    }
+}
+
+private final class ForceCastRuleVisitor: SyntaxVisitor {
+    var positions: [AbsolutePosition] = []
+
+    override func visitPost(_ node: AsExprSyntax) {
+        if node.questionOrExclamationMark?.tokenKind == .exclamationMark {
+            positions.append(node.asTok.positionAfterSkippingLeadingTrivia)
         }
     }
 }