[TypeChecker] Do not attempt to skip typechecking for didSet

lib/SILOptimizer/UtilityPasses/NonInlinableFunctionSkippingChecker.cpp

@@ -65,6 +65,12 @@ static bool shouldHaveSkippedFunction(const SILFunction &F) {
   if (isa<DestructorDecl>(func) || isa<ConstructorDecl>(func))
     return false;
 
+  // See DeclChecker::shouldSkipBodyTypechecking. Can't skip didSet for now.
+  if (auto *AD = dyn_cast<AccessorDecl>(func)) {
+    if (AD->getAccessorKind() == AccessorKind::DidSet)
+      return false;
+  }
+
   // If none of those conditions trip, then this is something that _should_
   // be serialized in the module even when we're skipping non-inlinable
   // function bodies.

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2332,6 +2332,13 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     if (!AFD->getBodySourceRange().isValid())
       return false;
 
+    // didSet runs typechecking to determine whether to keep its parameter,
+    // so never try to skip.
+    if (auto *AD = dyn_cast<AccessorDecl>(AFD)) {
+      if (AD->getAccessorKind() == AccessorKind::DidSet)
+        return false;
+    }
+
     // If we're gonna serialize the body, we can't skip it.
     if (AFD->getResilienceExpansion() == ResilienceExpansion::Minimal)
       return false;

test/Frontend/skip-non-inlinable-function-bodies.swift

@@ -157,6 +157,18 @@ public struct Struct {
     }
   }
 
+  public var willSetVar: Int = 1 {
+    willSet {
+      _blackHole("willSet body") // CHECK-NOT: "willSet body"
+    }
+  }
+
+  public var didSetVar: Int = 1 {
+    didSet {
+      _blackHole("didSet body") // CHECK-NOT: "didSet body"
+    }
+  }
+
   @_transparent
   public func transparentFunc() {
     _blackHole("@_transparent method body") // CHECK: "@_transparent method body"

validation-test/compiler_crashers_2_fixed/rdar70739449.swift

@@ -0,0 +1,9 @@
+// RUN: %target-swift-frontend -emit-module %s -experimental-skip-non-inlinable-function-bodies
+
+struct Foo {
+  var fieldWithDidSet : Int {
+    didSet {
+      let local = oldValue
+    }
+  }
+}