[CS] Invalidate auxiliary vars in markInvalid

And make sure we mark any PatternBindingDecl entries as having
been checked to avoid re-checking. This fixes a crash where we could
attempt to re-check a property wrapper to compute its backing type.

Author: hamishknight

lib/Sema/SyntacticElementTarget.cpp

@@ -306,14 +306,31 @@ void SyntacticElementTarget::markInvalid() const {
       return Action::Continue(P);
     }
 
+    void invalidateVarDecl(VarDecl *VD) {
+      // Only set invalid if we don't already have an interface type computed.
+      if (!VD->hasInterfaceType())
+        VD->setInvalid();
+
+      // Also do the same for any auxiliary vars.
+      VD->visitAuxiliaryVars(/*forNameLookup*/ false, [&](VarDecl *VD) {
+        invalidateVarDecl(VD);
+      });
+    }
+
     PreWalkAction walkToDeclPre(Decl *D) override {
       // Mark any VarDecls and PatternBindingDecls as invalid.
       if (auto *VD = dyn_cast<VarDecl>(D)) {
-        // Only set invalid if we don't already have an interface type computed.
-        if (!VD->hasInterfaceType())
-          D->setInvalid();
-      } else if (isa<PatternBindingDecl>(D)) {
-        D->setInvalid();
+        invalidateVarDecl(VD);
+      } else if (auto *PBD = dyn_cast<PatternBindingDecl>(D)) {
+        PBD->setInvalid();
+        // Make sure we mark the patterns and initializers as having been
+        // checked, otherwise `typeCheckPatternBinding` might try to check them
+        // again.
+        for (auto i : range(0, PBD->getNumPatternEntries())) {
+          PBD->setPattern(i, PBD->getPattern(i), /*fullyValidated*/ true);
+          if (PBD->isInitialized(i))
+            PBD->setInitializerChecked(i);
+        }
       }
       return Action::VisitNodeIf(isa<PatternBindingDecl>(D));
     }

validation-test/compiler_crashers_fixed/ConstraintSystem-getClosureType-4a4392.swift

@@ -0,0 +1,11 @@
+// {"kind":"typecheck","signature":"swift::constraints::ConstraintSystem::getClosureType(swift::ClosureExpr const*) const","signatureAssert":"Assertion failed: (result), function getClosureType"}
+// RUN: not %target-swift-frontend -typecheck %s
+@propertyWrapper struct a {
+}
+{
+  @a var x =
+    if <#expression#> {
+      return
+    }
+  _x
+}