Fix ignore-unparsable-files flag so that it works.

The flag was broken after SwiftSyntax switched how it represents unsupported syntax nodes, from Unknown* type nodes to Missing* nodes. Now the tool exits early whenever there are parsing diagnostics, and `--ignore-unparsable-files` disables emitting those diagnostics. Regardless of the flag's value, the formatter won't try to operate on a file with any parsing diagnostics.

Package.swift

@@ -122,14 +122,6 @@ let package = Package(
       ]
     ),
 
-    .testTarget(
-      name: "SwiftFormatTests",
-      dependencies: [
-        "SwiftFormat",
-        .product(name: "SwiftSyntax", package: "swift-syntax"),
-        .product(name: "SwiftParser", package: "swift-syntax"),
-      ]
-    ),
     .testTarget(
       name: "SwiftFormatConfigurationTests",
       dependencies: ["SwiftFormatConfiguration"]

Sources/SwiftFormat/Parsing.swift

@@ -40,15 +40,19 @@ func parseAndEmitDiagnostics(
   let sourceFile =
     try operatorTable.foldAll(Parser.parse(source: source)) { _ in }.as(SourceFileSyntax.self)!
 
+  let diagnostics = ParseDiagnosticsGenerator.diagnostics(for: sourceFile)
   if let parsingDiagnosticHandler = parsingDiagnosticHandler {
     let expectedConverter =
       SourceLocationConverter(file: url?.path ?? "<unknown>", tree: sourceFile)
-    let diagnostics = ParseDiagnosticsGenerator.diagnostics(for: sourceFile)
     for diagnostic in diagnostics {
       let location = diagnostic.location(converter: expectedConverter)
       parsingDiagnosticHandler(diagnostic, location)
     }
   }
 
+  guard diagnostics.isEmpty else {
+    throw SwiftFormatError.fileContainsInvalidSyntax
+  }
+
   return sourceFile
 }

Sources/SwiftFormat/SwiftFormatError.swift

@@ -22,5 +22,5 @@ public enum SwiftFormatError: Error {
   case isDirectory
 
   /// The file contains invalid or unrecognized Swift syntax and cannot be handled safely.
-  case fileContainsInvalidSyntax(position: AbsolutePosition)
+  case fileContainsInvalidSyntax
 }

Sources/SwiftFormat/SwiftFormatter.swift

@@ -146,10 +146,6 @@ public final class SwiftFormatter {
     syntax: SourceFileSyntax, operatorTable: OperatorTable,
     assumingFileURL url: URL?, source: String?, to outputStream: inout Output
   ) throws {
-    if let position = _firstInvalidSyntaxPosition(in: Syntax(syntax)) {
-      throw SwiftFormatError.fileContainsInvalidSyntax(position: position)
-    }
-
     let assumedURL = url ?? URL(fileURLWithPath: "source")
     let context = Context(
       configuration: configuration, operatorTable: operatorTable, findingConsumer: findingConsumer,

Sources/SwiftFormat/SwiftLinter.swift

@@ -134,10 +134,6 @@ public final class SwiftLinter {
     assumingFileURL url: URL,
     source: String?
   ) throws {
-    if let position = _firstInvalidSyntaxPosition(in: Syntax(syntax)) {
-      throw SwiftFormatError.fileContainsInvalidSyntax(position: position)
-    }
-
     let context = Context(
       configuration: configuration, operatorTable: operatorTable, findingConsumer: findingConsumer,
       fileURL: url, sourceFileSyntax: syntax, source: source, ruleNameCache: ruleNameCache)

Sources/swift-format/Frontend/FormatFrontend.swift

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
+import SwiftDiagnostics
 import SwiftFormat
 import SwiftFormatConfiguration
 import SwiftSyntax
@@ -39,6 +40,13 @@ class FormatFrontend: Frontend {
       return
     }
 
+    let diagnosticHandler: (Diagnostic, SourceLocation) -> () =  { (diagnostic, location) in
+      guard !self.lintFormatOptions.ignoreUnparsableFiles else {
+        // No diagnostics should be emitted in this mode.
+        return
+      }
+      self.diagnosticsEngine.consumeParserDiagnostic(diagnostic, location)
+    }
     var stdoutStream = FileHandleTextOutputStream(FileHandle.standardOutput)
     do {
       if inPlace {
@@ -47,7 +55,7 @@ class FormatFrontend: Frontend {
           source: source,
           assumingFileURL: url,
           to: &buffer,
-          parsingDiagnosticHandler: diagnosticsEngine.consumeParserDiagnostic)
+          parsingDiagnosticHandler: diagnosticHandler)
 
         if buffer != source {
           let bufferData = buffer.data(using: .utf8)!  // Conversion to UTF-8 cannot fail
@@ -58,13 +66,13 @@ class FormatFrontend: Frontend {
           source: source,
           assumingFileURL: url,
           to: &stdoutStream,
-          parsingDiagnosticHandler: diagnosticsEngine.consumeParserDiagnostic)
+          parsingDiagnosticHandler: diagnosticHandler)
       }
     } catch SwiftFormatError.fileNotReadable {
       diagnosticsEngine.emitError(
         "Unable to format \(url.relativePath): file is not readable or does not exist.")
       return
-    } catch SwiftFormatError.fileContainsInvalidSyntax(let position) {
+    } catch SwiftFormatError.fileContainsInvalidSyntax {
       guard !lintFormatOptions.ignoreUnparsableFiles else {
         guard !inPlace else {
           // For in-place mode, nothing is expected to stdout and the file shouldn't be modified.
@@ -73,9 +81,7 @@ class FormatFrontend: Frontend {
         stdoutStream.write(source)
         return
       }
-      let location = SourceLocationConverter(file: url.path, source: source).location(for: position)
-      diagnosticsEngine.emitError(
-        "file contains invalid or unrecognized Swift syntax.", location: location)
+      // Otherwise, relevant diagnostics about the problematic nodes have been emitted.
       return
     } catch {
       diagnosticsEngine.emitError("Unable to format \(url.relativePath): \(error)")

Sources/swift-format/Frontend/LintFrontend.swift

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
+import SwiftDiagnostics
 import SwiftFormat
 import SwiftFormatConfiguration
 import SwiftSyntax
@@ -32,20 +33,24 @@ class LintFrontend: Frontend {
     do {
       try linter.lint(
         source: source,
-        assumingFileURL: url,
-        parsingDiagnosticHandler: diagnosticsEngine.consumeParserDiagnostic)
+        assumingFileURL: url) { (diagnostic, location) in
+          guard !self.lintFormatOptions.ignoreUnparsableFiles else {
+            // No diagnostics should be emitted in this mode.
+            return
+          }
+          self.diagnosticsEngine.consumeParserDiagnostic(diagnostic, location)
+      }
+
     } catch SwiftFormatError.fileNotReadable {
       diagnosticsEngine.emitError(
         "Unable to lint \(url.relativePath): file is not readable or does not exist.")
       return
-    } catch SwiftFormatError.fileContainsInvalidSyntax(let position) {
+    } catch SwiftFormatError.fileContainsInvalidSyntax {
       guard !lintFormatOptions.ignoreUnparsableFiles else {
         // The caller wants to silently ignore this error.
         return
       }
-      let location = SourceLocationConverter(file: url.path, source: source).location(for: position)
-      diagnosticsEngine.emitError(
-        "file contains invalid or unrecognized Swift syntax.", location: location)
+      // Otherwise, relevant diagnostics about the problematic nodes have been emitted.
       return
     } catch {
       diagnosticsEngine.emitError("Unable to lint \(url.relativePath): \(error)")