Flesh out unknown node handling.

We previously only covered a subset of the unknown nodes. Treat them
all as verbatim text so that malformed or unrecognized syntax does
not get completely clobbered. (Note that in some cases, depending on
how breaks/spaces are inserted into the token stream relative to tokens
in the unknown nodes, leading spaces may still get compressed).

Author: allevato

Sources/SwiftFormatPrettyPrint/TokenStreamCreator.swift

@@ -1658,10 +1658,6 @@ private final class TokenStreamCreator: SyntaxVisitor {
     return .visitChildren
   }
 
-  override func visit(_ node: UnknownPatternSyntax) -> SyntaxVisitorContinueKind {
-    return .visitChildren
-  }
-
   override func visit(_ node: SomeTypeSyntax) -> SyntaxVisitorContinueKind {
     after(node.someSpecifier, tokens: .space)
     return .visitChildren
@@ -1937,18 +1933,45 @@ private final class TokenStreamCreator: SyntaxVisitor {
     return .visitChildren
   }
 
+  // MARK: - Nodes representing unknown or malformed syntax
+
   override func visit(_ node: UnknownDeclSyntax) -> SyntaxVisitorContinueKind {
     verbatimToken(Syntax(node))
-    // Visiting children is not needed here.
+    return .skipChildren
+  }
+
+  override func visit(_ node: UnknownExprSyntax) -> SyntaxVisitorContinueKind {
+    verbatimToken(Syntax(node))
+    return .skipChildren
+  }
+
+  override func visit(_ node: UnknownPatternSyntax) -> SyntaxVisitorContinueKind {
+    verbatimToken(Syntax(node))
     return .skipChildren
   }
 
   override func visit(_ node: UnknownStmtSyntax) -> SyntaxVisitorContinueKind {
     verbatimToken(Syntax(node))
-    // Visiting children is not needed here.
     return .skipChildren
   }
 
+  override func visit(_ node: UnknownSyntax) -> SyntaxVisitorContinueKind {
+    verbatimToken(Syntax(node))
+    return .skipChildren
+  }
+
+  override func visit(_ node: UnknownTypeSyntax) -> SyntaxVisitorContinueKind {
+    verbatimToken(Syntax(node))
+    return .skipChildren
+  }
+
+  override func visit(_ node: NonEmptyTokenListSyntax) -> SyntaxVisitorContinueKind {
+    verbatimToken(Syntax(node))
+    return .skipChildren
+  }
+
+  // MARK: - Token handling
+
   override func visit(_ token: TokenSyntax) -> SyntaxVisitorContinueKind {
     // Arrange the tokens and trivia such that before tokens that start a new "scope" (which may
     // increase indentation) are inserted in the stream *before* the leading trivia, but tokens

Tests/SwiftFormatPrettyPrintTests/UnknownDeclTests.swift

@@ -0,0 +1,81 @@
+/// Tests for unknown/malformed nodes that ensure that they are handled as verbatim text so that
+/// their internal tokens do not get squashed together.
+final class UnknownNodeTests: PrettyPrintTestCase {
+  func testUnknownDecl() {
+    let input =
+      """
+      struct MyStruct where {
+        let a = 123
+      }
+      """
+
+    assertPrettyPrintEqual(input: input, expected: input + "\n", linelength: 45)
+  }
+
+  func testUnknownExpr() {
+    let input =
+      """
+      (foo where bar)
+      """
+
+    assertPrettyPrintEqual(input: input, expected: input + "\n", linelength: 45)
+  }
+
+  func testUnknownPattern() {
+    // This one loses the space after the word `case` because the break would normally be
+    // inserted before the first token in the pattern.
+    let input =
+      """
+      if case * ! = x {
+        bar()
+      }
+      """
+
+    let expected =
+      """
+      if case* ! = x {
+        bar()
+      }
+
+      """
+
+    assertPrettyPrintEqual(input: input, expected: expected, linelength: 45)
+  }
+
+  func testUnknownStmt() {
+    let input =
+      """
+      if foo where {
+        bar()
+      }
+      """
+
+    assertPrettyPrintEqual(input: input, expected: input + "\n", linelength: 45)
+  }
+
+  func testUnknownType() {
+    // This one loses the space after the colon because the break would normally be inserted before
+    // the first token in the type name.
+    let input =
+      """
+      let x: where
+      """
+
+    let expected =
+      """
+      let x:where
+
+      """
+
+    assertPrettyPrintEqual(input: input, expected: expected, linelength: 45)
+  }
+
+  func testNonEmptyTokenList() {
+    let input =
+      """
+      @(foo ! @ # bar)
+      """
+
+    assertPrettyPrintEqual(input: input, expected: input + "\n", linelength: 45)
+  }
+}

Tests/SwiftFormatPrettyPrintTests/UnknownNodeTests.swift

@@ -705,12 +705,17 @@ extension TypeAliasTests {
     ]
 }
 
-extension UnknownDeclTests {
+extension UnknownNodeTests {
     // DO NOT MODIFY: This is autogenerated, use:
     //   `swift test --generate-linuxmain`
     // to regenerate.
-    static let __allTests__UnknownDeclTests = [
+    static let __allTests__UnknownNodeTests = [
+        ("testNonEmptyTokenList", testNonEmptyTokenList),
         ("testUnknownDecl", testUnknownDecl),
+        ("testUnknownExpr", testUnknownExpr),
+        ("testUnknownPattern", testUnknownPattern),
+        ("testUnknownStmt", testUnknownStmt),
+        ("testUnknownType", testUnknownType),
     ]
 }
 
@@ -795,7 +800,7 @@ public func __allTests() -> [XCTestCaseEntry] {
         testCase(TryCatchTests.__allTests__TryCatchTests),
         testCase(TupleDeclTests.__allTests__TupleDeclTests),
         testCase(TypeAliasTests.__allTests__TypeAliasTests),
-        testCase(UnknownDeclTests.__allTests__UnknownDeclTests),
+        testCase(UnknownNodeTests.__allTests__UnknownNodeTests),
         testCase(VariableDeclarationTests.__allTests__VariableDeclarationTests),
         testCase(WhileStmtTests.__allTests__WhileStmtTests),
         testCase(YieldStmtTests.__allTests__YieldStmtTests),