Don’t offer text edits from inlay hints if they are syntactically invalid

Don’t offer any text edits for inlay hints displayed in closure paramters or enum case items.

Fixes #759
rdar://111559715

Author: ahoppen

Sources/SourceKitLSP/Swift/SwiftLanguageServer.swift

@@ -1320,13 +1320,17 @@ extension SwiftLanguageServer {
           .map { info -> InlayHint in
             let position = info.range.upperBound
             let label = ": \(info.printedType)"
+            let textEdits: [TextEdit]?
+            if info.canBeFollowedByTypeAnnotation {
+              textEdits = [TextEdit(range: position..<position, newText: label)]
+            } else {
+              textEdits = nil
+            }
             return InlayHint(
               position: position,
               label: .string(label),
               kind: .type,
-              textEdits: [
-                TextEdit(range: position..<position, newText: label)
-              ]
+              textEdits: textEdits
             )
           }
 

Sources/SourceKitLSP/Swift/VariableTypeInfo.swift

@@ -13,6 +13,35 @@
 import Dispatch
 import LanguageServerProtocol
 import SourceKitD
+import SwiftSyntax
+
+fileprivate extension TokenSyntax {
+  /// Returns `false` if it is known that this token can’t be followed by a type
+  /// annotation.
+  var canBeFollowedByTypeAnnotation: Bool {
+    var node = Syntax(self)
+    LOOP: while let parent = node.parent {
+      switch parent.kind {
+      case .caseItem, .closureParam:
+        // case items (inside a switch) and closure parameters can’t have type
+        // annotations.
+        return false
+      case .codeBlockItem, .memberDeclListItem:
+        // Performanc optimization. If we walked the parents up to code block item,
+        // we can’t enter a case item or closure param anymore. No need walking
+        // the tree any further.
+        break LOOP
+      default:
+        break
+      }
+      node = parent
+    }
+
+    // By default, assume that the token can be followed by a type annotation as
+    // most locations that produce a variable type info can.
+    return true
+  }
+}
 
 /// A typed variable as returned by sourcekitd's CollectVariableType.
 struct VariableTypeInfo {
@@ -22,6 +51,9 @@ struct VariableTypeInfo {
   var printedType: String
   /// Whether the variable has an explicit type annotation in the source file.
   var hasExplicitType: Bool
+  /// Whether we should suggest making an edit to add the type annotation to the
+  /// source file.
+  var canBeFollowedByTypeAnnotation: Bool
 
   init?(_ dict: SKDResponseDictionary, in snapshot: DocumentSnapshot) {
     let keys = dict.sourcekitd.keys
@@ -34,10 +66,12 @@ struct VariableTypeInfo {
           let hasExplicitType: Bool = dict[keys.variable_type_explicit] else {
       return nil
     }
+    let tokenAtOffset = snapshot.tokens.syntaxTree?.token(at: AbsolutePosition(utf8Offset: offset))
 
     self.range = startIndex..<endIndex
     self.printedType = printedType
     self.hasExplicitType = hasExplicitType
+    self.canBeFollowedByTypeAnnotation = tokenAtOffset?.canBeFollowedByTypeAnnotation ?? true
   }
 }
 

Tests/SourceKitLSPTests/InlayHintTests.swift

@@ -61,14 +61,18 @@ final class InlayHintTests: XCTestCase {
     }
   }
 
-  private func makeInlayHint(position: Position, kind: InlayHintKind, label: String) -> InlayHint {
-    InlayHint(
+  private func makeInlayHint(position: Position, kind: InlayHintKind, label: String, hasEdit: Bool = true) -> InlayHint {
+    let textEdits: [TextEdit]?
+    if hasEdit {
+      textEdits = [TextEdit(range: position..<position, newText: label)]
+    } else {
+      textEdits = nil
+    }
+    return InlayHint(
       position: position,
       label: .string(label),
       kind: kind,
-      textEdits: [
-        TextEdit(range: position..<position, newText: label)
-      ]
+      textEdits: textEdits
     )
   }
 
@@ -205,7 +209,8 @@ final class InlayHintTests: XCTestCase {
       makeInlayHint(
         position: Position(line: 3, utf16index: 31),
         kind: .type,
-        label: ": String"
+        label: ": String",
+        hasEdit: false
       ),
       makeInlayHint(
         position: Position(line: 4, utf16index: 40),