[AST] Generalize getInnermostClosureForSelfCapture

Really this applies to any capture, not just
`self`. Also refactor to make it clear that
parent closures and functions are really the only
cases that matter here.

Author: hamishknight

include/swift/AST/DeclContext.h

@@ -515,12 +515,12 @@ class alignas(1 << DeclContextAlignInBits) DeclContext
         const_cast<DeclContext *>(this)->getInnermostSkippedFunctionContext();
   }
 
-  /// Returns the innermost context that is a ClosureExpr, which defines how
-  /// self behaves, unless within a type context that redefines self.
+  /// Returns the innermost ClosureExpr context that can propagate its captures
+  /// to this DeclContext.
   LLVM_READONLY
-  ClosureExpr *getInnermostClosureForSelfCapture();
-  const ClosureExpr *getInnermostClosureForSelfCapture() const {
-    return const_cast<DeclContext *>(this)->getInnermostClosureForSelfCapture();
+  ClosureExpr *getInnermostClosureForCaptures();
+  const ClosureExpr *getInnermostClosureForCaptures() const {
+    return const_cast<DeclContext *>(this)->getInnermostClosureForCaptures();
   }
 
   /// Returns the semantic parent of this context.  A context has a

lib/AST/DeclContext.cpp

@@ -280,21 +280,21 @@ DeclContext *DeclContext::getInnermostSkippedFunctionContext() {
   return nullptr;
 }
 
-ClosureExpr *DeclContext::getInnermostClosureForSelfCapture() {
-  auto dc = this;
-  if (auto closure = dyn_cast<ClosureExpr>(dc)) {
-    return closure;
-  }
-
-  // Stop searching if we find a type decl, since types always
-  // redefine what 'self' means, even when nested inside a closure.
-  if (dc->isTypeContext()) {
-    return nullptr;
-  }
+ClosureExpr *DeclContext::getInnermostClosureForCaptures() {
+  auto *DC = this;
+  do {
+    if (auto *CE = dyn_cast<ClosureExpr>(DC))
+      return CE;
 
-  if (auto parent = dc->getParent()) {
-    return parent->getInnermostClosureForSelfCapture();
-  }
+    // Autoclosures and AbstractFunctionDecls can propagate captures.
+    switch (DC->getContextKind()) {
+    case DeclContextKind::AbstractClosureExpr:
+    case DeclContextKind::AbstractFunctionDecl:
+      continue;
+    default:
+      return nullptr;
+    }
+  } while ((DC = DC->getParent()));
 
   return nullptr;
 }

lib/AST/UnqualifiedLookup.cpp

@@ -362,7 +362,7 @@ ValueDecl *UnqualifiedLookupFactory::lookupBaseDecl(const DeclContext *baseDC) c
   // Perform an unqualified lookup for the base decl of this result. This
   // handles cases where self was rebound (e.g. `guard let self = self`)
   // earlier in this closure or some outer closure.
-  auto closureExpr = DC->getInnermostClosureForSelfCapture();
+  auto closureExpr = DC->getInnermostClosureForCaptures();
   if (!closureExpr) {
     return nullptr;
   }

lib/Sema/MiscDiagnostics.cpp

@@ -2221,7 +2221,7 @@ static void diagnoseImplicitSelfUseInClosure(const Expr *E,
         return nullptr;
       }
 
-      return parentContext->getInnermostClosureForSelfCapture();
+      return parentContext->getInnermostClosureForCaptures();
     }
 
     bool shouldRecordClosure(const AbstractClosureExpr *E) {