[Sema] Generate TRC for unparsed functions right before type-checking

Fix an issue where `if #available(...)` conditions were ignored in
emit-module-separately builds or when skipping non-inlinable function
bodies.

To handle functions for which parsing is delayed but type-checking is
not delayed, move up building the delayed TRC to the
TypeCheckFunctionBodyRequest service.

rdar://83166742

Author: xymus

include/swift/AST/SourceFile.h

@@ -515,7 +515,7 @@ class SourceFile final : public FileUnit {
   /// null if the context hierarchy has not been built yet. Use
   /// TypeChecker::getOrBuildTypeRefinementContext() to get a built
   /// root of the hierarchy.
-  TypeRefinementContext *getTypeRefinementContext();
+  TypeRefinementContext *getTypeRefinementContext() const;
 
   /// Set the root refinement context for the file.
   void setTypeRefinementContext(TypeRefinementContext *TRC);

lib/AST/Module.cpp

@@ -2892,7 +2892,7 @@ SynthesizedFileUnit &SourceFile::getOrCreateSynthesizedFile() {
   return *SynthesizedFile;
 }
 
-TypeRefinementContext *SourceFile::getTypeRefinementContext() {
+TypeRefinementContext *SourceFile::getTypeRefinementContext() const {
   return TRC;
 }
 

lib/Sema/TypeCheckStmt.cpp

@@ -1955,6 +1955,10 @@ TypeCheckFunctionBodyRequest::evaluate(Evaluator &evaluator,
   if (tyOpts.DebugTimeFunctionBodies || tyOpts.WarnLongFunctionBodies)
     timer.emplace(AFD);
 
+  auto SF = AFD->getParentSourceFile();
+  if (SF)
+    TypeChecker::buildTypeRefinementContextHierarchyDelayed(*SF, AFD);
+
   BraceStmt *body = AFD->getBody();
   assert(body && "Expected body to type-check");
 

lib/Sema/TypeChecker.cpp

@@ -252,9 +252,6 @@ static void typeCheckDelayedFunctions(SourceFile &SF) {
   while (currentFunctionIdx < SF.DelayedFunctions.size()) {
     auto *AFD = SF.DelayedFunctions[currentFunctionIdx];
     assert(!AFD->getDeclContext()->isLocalContext());
-
-    TypeChecker::buildTypeRefinementContextHierarchyDelayed(SF, AFD);
-
     (void) AFD->getTypecheckedBody();
     ++currentFunctionIdx;
   }

test/Sema/availability_and_delayed_parsing.swift

@@ -17,6 +17,18 @@ public func foo() { }
 // TRC-API: (root versions=[10.10.0,+Inf)
 // TRC-API:   (decl versions=[10.12,+Inf) decl=foo()
 
+struct S {
+  fileprivate var actual: [String] = [] {
+    didSet {
+      if #available(macOS 10.15, *) {
+        foo()
+      }
+    }
+  }
+}
+// TRC-API:  (condition_following_availability versions=[10.15,+Inf)
+// TRC-API:  (if_then versions=[10.15,+Inf)
+
 @inlinable public func inlinableFunc() {
     if #available(macOS 10.12, *) {
         foo()