[Sema] Walk patterns for syntactic diagnostics

Use `SyntacticElementTarget::walk`, ensuring we
walk to any ExprPatterns.

lib/Sema/MiscDiagnostics.cpp

@@ -127,10 +127,6 @@ static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
       return MacroWalking::Expansion;
     }
 
-    PreWalkResult<Pattern *> walkToPatternPre(Pattern *P) override {
-      return Action::SkipNode(P);
-    }
-
     PreWalkAction walkToTypeReprPre(TypeRepr *T) override {
       return Action::Continue();
     }

lib/Sema/TypeCheckConstraints.cpp

@@ -327,20 +327,31 @@ void ParentConditionalConformance::diagnoseConformanceStack(
 }
 
 namespace {
-/// Produce any additional syntactic diagnostics for the body of a function
-/// that had a result builder applied.
-class FunctionSyntacticDiagnosticWalker : public ASTWalker {
+/// Produce any additional syntactic diagnostics for a SyntacticElementTarget.
+class SyntacticDiagnosticWalker final : public ASTWalker {
   SmallVector<DeclContext *, 4> dcStack;
+  const SyntacticElementTarget &Target;
+  bool IsTopLevelExprStmt;
+
+  SyntacticDiagnosticWalker(const SyntacticElementTarget &target,
+                            bool isExprStmt)
+      : Target(target), IsTopLevelExprStmt(isExprStmt) {
+    dcStack.push_back(target.getDeclContext());
+  }
 
 public:
-  FunctionSyntacticDiagnosticWalker(DeclContext *dc) { dcStack.push_back(dc); }
+  static void check(const SyntacticElementTarget &target, bool isExprStmt) {
+    auto walker = SyntacticDiagnosticWalker(target, isExprStmt);
+    target.walk(walker);
+  }
 
   MacroWalking getMacroWalkingBehavior() const override {
     return MacroWalking::Expansion;
   }
 
   PreWalkResult<Expr *> walkToExprPre(Expr *expr) override {
-    performSyntacticExprDiagnostics(expr, dcStack.back(), /*isExprStmt=*/false);
+    auto isExprStmt = (expr == Target.getAsExpr()) ? IsTopLevelExprStmt : false;
+    performSyntacticExprDiagnostics(expr, dcStack.back(), isExprStmt);
 
     if (auto closure = dyn_cast<ClosureExpr>(expr)) {
       if (closure->isSeparatelyTypeChecked()) {
@@ -368,9 +379,10 @@ public:
     return Action::Continue(stmt);
   }
 
-  PreWalkResult<Pattern *> walkToPatternPre(Pattern *pattern) override {
-    return Action::SkipNode(pattern);
+  PreWalkAction walkToDeclPre(Decl *D) override {
+    return Action::VisitNodeIf(isa<PatternBindingDecl>(D));
   }
+
   PreWalkAction walkToTypeReprPre(TypeRepr *typeRepr) override {
     return Action::SkipNode();
   }
@@ -382,41 +394,7 @@ public:
 
 void constraints::performSyntacticDiagnosticsForTarget(
     const SyntacticElementTarget &target, bool isExprStmt) {
-  auto *dc = target.getDeclContext();
-  switch (target.kind) {
-  case SyntacticElementTarget::Kind::expression: {
-    // First emit diagnostics for the main expression.
-    performSyntacticExprDiagnostics(target.getAsExpr(), dc, isExprStmt);
-    return;
-  }
-
-  case SyntacticElementTarget::Kind::forEachPreamble: {
-    auto *stmt = target.getAsForEachStmt();
-
-    // First emit diagnostics for the main expression.
-    performSyntacticExprDiagnostics(stmt->getTypeCheckedSequence(), dc,
-                                    isExprStmt);
-
-    if (auto *whereExpr = stmt->getWhere())
-      performSyntacticExprDiagnostics(whereExpr, dc, /*isExprStmt*/ false);
-    return;
-  }
-
-  case SyntacticElementTarget::Kind::function: {
-    auto *body = target.getFunctionBody();
-    FunctionSyntacticDiagnosticWalker walker(dc);
-    body->walk(walker);
-    return;
-  }
-  case SyntacticElementTarget::Kind::closure:
-  case SyntacticElementTarget::Kind::stmtCondition:
-  case SyntacticElementTarget::Kind::caseLabelItem:
-  case SyntacticElementTarget::Kind::patternBinding:
-  case SyntacticElementTarget::Kind::uninitializedVar:
-    // Nothing to do for these.
-    return;
-  }
-  llvm_unreachable("Unhandled case in switch!");
+  SyntacticDiagnosticWalker::check(target, isExprStmt);
 }
 
 #pragma mark High-level entry points

test/Sema/issue-75389.swift

@@ -0,0 +1,55 @@
+// RUN: %target-typecheck-verify-swift
+
+// https://github.com/swiftlang/swift/issues/75389
+
+@available(*, unavailable)
+func unavailableFn() -> Int { 0 }
+// expected-note@-1 5{{'unavailableFn()' has been explicitly marked unavailable here}}
+
+if case unavailableFn() = 0 {}
+// expected-error@-1 {{'unavailableFn()' is unavailable}}
+
+switch Bool.random() {
+case true where unavailableFn() == 1:
+  // expected-error@-1 {{'unavailableFn()' is unavailable}}
+  break
+default:
+  break
+}
+switch 0 {
+case unavailableFn():
+  // expected-error@-1 {{'unavailableFn()' is unavailable}}
+  break
+default:
+  break
+}
+let _ = {
+  switch Bool.random() {
+  case true where unavailableFn() == 1:
+    // expected-error@-1 {{'unavailableFn()' is unavailable}}
+    break
+  default:
+    break
+  }
+  switch 0 {
+  case unavailableFn():
+    // expected-error@-1 {{'unavailableFn()' is unavailable}}
+    break
+  default:
+    break
+  }
+}
+
+struct S {}
+
+func ~= (lhs: S.Type, rhs: S.Type) -> Bool { true }
+
+if case (S) = S.self {}
+// expected-error@-1 {{expected member name or initializer call after type name}}
+// expected-note@-2 {{add arguments after the type to construct a value of the type}}
+// expected-note@-3 {{use '.self' to reference the type object}}
+
+if case ({ if case (S) = S.self { true } else { false } }()) = true {}
+// expected-error@-1 {{expected member name or initializer call after type name}}
+// expected-note@-2 {{add arguments after the type to construct a value of the type}}
+// expected-note@-3 {{use '.self' to reference the type object}}