Generalize optional chaining detection used by #require(). (#625)

This PR generalizes the optional chaining detection used in the
implementation of unwrapping `#require()` such that it works with more
than just member access expressions.

Resolves #623.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/TestingMacros/Support/ConditionArgumentParsing.swift

@@ -242,6 +242,18 @@ private func _parseCondition(from expr: ClosureExprSyntax, for macro: some Frees
   return Condition(expression: expr)
 }
 
+/// A class that walks a syntax tree looking for optional chaining expressions
+/// such as `a?.b.c`.
+private final class _OptionalChainFinder: SyntaxVisitor {
+  /// Whether or not any optional chaining was found.
+  var optionalChainFound = false
+
+  override func visit(_ node: OptionalChainingExprSyntax) -> SyntaxVisitorContinueKind {
+    optionalChainFound = true
+    return .skipChildren
+  }
+}
+
 /// Extract the underlying expression from an optional-chained expression as
 /// well as the number of question marks required to reach it.
 ///
@@ -279,15 +291,9 @@ private func _exprFromOptionalChainedExpr(_ expr: some ExprSyntaxProtocol) -> (E
   // the member accesses in the expression use optional chaining and, if one
   // does, ensure we preserve optional chaining in the macro expansion.
   if questionMarkCount == 0 {
-    func isOptionalChained(_ expr: some ExprSyntaxProtocol) -> Bool {
-      if expr.is(OptionalChainingExprSyntax.self) {
-        return true
-      } else if let memberAccessBaseExpr = expr.as(MemberAccessExprSyntax.self)?.base {
-        return isOptionalChained(memberAccessBaseExpr)
-      }
-      return false
-    }
-    if isOptionalChained(originalExpr) {
+    let optionalChainFinder = _OptionalChainFinder(viewMode: .sourceAccurate)
+    optionalChainFinder.walk(originalExpr)
+    if optionalChainFinder.optionalChainFound {
       questionMarkCount = 1
     }
   }

Tests/TestingMacrosTests/ConditionMacroTests.swift

@@ -88,6 +88,8 @@ struct ConditionMacroTests {
         ##"Testing.__checkPropertyAccess(a.self, getting: { $0???.isB }, expression: .__fromPropertyAccess(.__fromSyntaxNode("a"), .__fromSyntaxNode("isB")), comments: [], isRequired: false, sourceLocation: Testing.SourceLocation.__here()).__expected()"##,
       ##"#expect(a?.b.isB)"##:
         ##"Testing.__checkPropertyAccess(a?.b.self, getting: { $0?.isB }, expression: .__fromPropertyAccess(.__fromSyntaxNode("a?.b"), .__fromSyntaxNode("isB")), comments: [], isRequired: false, sourceLocation: Testing.SourceLocation.__here()).__expected()"##,
+      ##"#expect(a?.b().isB)"##:
+        ##"Testing.__checkPropertyAccess(a?.b().self, getting: { $0?.isB }, expression: .__fromPropertyAccess(.__fromSyntaxNode("a?.b()"), .__fromSyntaxNode("isB")), comments: [], isRequired: false, sourceLocation: Testing.SourceLocation.__here()).__expected()"##,
       ##"#expect(isolation: somewhere) {}"##:
         ##"Testing.__checkClosureCall(performing: {}, expression: .__fromSyntaxNode("{}"), comments: [], isRequired: false, isolation: somewhere, sourceLocation: Testing.SourceLocation.__here()).__expected()"##,
     ]
@@ -166,6 +168,8 @@ struct ConditionMacroTests {
         ##"Testing.__checkPropertyAccess(a.self, getting: { $0???.isB }, expression: .__fromPropertyAccess(.__fromSyntaxNode("a"), .__fromSyntaxNode("isB")), comments: [], isRequired: true, sourceLocation: Testing.SourceLocation.__here()).__required()"##,
       ##"#require(a?.b.isB)"##:
         ##"Testing.__checkPropertyAccess(a?.b.self, getting: { $0?.isB }, expression: .__fromPropertyAccess(.__fromSyntaxNode("a?.b"), .__fromSyntaxNode("isB")), comments: [], isRequired: true, sourceLocation: Testing.SourceLocation.__here()).__required()"##,
+      ##"#require(a?.b().isB)"##:
+        ##"Testing.__checkPropertyAccess(a?.b().self, getting: { $0?.isB }, expression: .__fromPropertyAccess(.__fromSyntaxNode("a?.b()"), .__fromSyntaxNode("isB")), comments: [], isRequired: true, sourceLocation: Testing.SourceLocation.__here()).__required()"##,
       ##"#require(isolation: somewhere) {}"##:
         ##"Testing.__checkClosureCall(performing: {}, expression: .__fromSyntaxNode("{}"), comments: [], isRequired: true, isolation: somewhere, sourceLocation: Testing.SourceLocation.__here()).__required()"##,
     ]

Tests/TestingTests/MiscellaneousTests.swift

@@ -222,6 +222,11 @@ struct MultiLineSuite {
   staticMultiLineTestDecl() async {}
 }
 
+@Test(.hidden) func complexOptionalChainingWithRequire() throws {
+  let x: String? = nil
+  _ = try #require(x?[...].last)
+}
+
 @Suite("Miscellaneous tests")
 struct MiscellaneousTests {
   @Test("Free function's name")