[CodeCompletion] Ensure all ExtensionDecl's extended nominal are computed

Fixes an assertion failure in ASTScope lookup

rdar://problem/67102794

Author: rintaro

lib/IDE/ExprContextAnalysis.cpp

@@ -46,9 +46,11 @@ void swift::ide::typeCheckContextAt(DeclContext *DC, SourceLoc Loc) {
   while (isa<AbstractClosureExpr>(DC))
     DC = DC->getParent();
 
-  // Make sure the extension has been bound, in case it is in an inactive #if
-  // or something weird like that.
+  // Make sure the extension has been bound.
   {
+    // Even if the extension is invalid (e.g. nested in a function or another
+    // type), we want to know the "intended nominal" of the extension so that
+    // we can know the type of 'Self'.
     SmallVector<ExtensionDecl *, 1> extensions;
     for (auto typeCtx = DC->getInnermostTypeContext(); typeCtx != nullptr;
          typeCtx = typeCtx->getParent()->getInnermostTypeContext()) {
@@ -59,6 +61,20 @@ void swift::ide::typeCheckContextAt(DeclContext *DC, SourceLoc Loc) {
       extensions.back()->computeExtendedNominal();
       extensions.pop_back();
     }
+
+    // If the completion happens in the inheritance clause of the extension,
+    // 'DC' is the parent of the extension. We need to iterate the top level
+    // decls to find it. In theory, we don't need the extended nominal in the
+    // inheritance clause, but ASTScope lookup requires that. We don't care
+    // unless 'DC' is not 'SourceFile' because non-toplevel extensions are
+    // 'canNeverBeBound()' anyway.
+    if (auto *SF = dyn_cast<SourceFile>(DC)) {
+      auto &SM = DC->getASTContext().SourceMgr;
+      for (auto *decl : SF->getTopLevelDecls())
+        if (auto *ext = dyn_cast<ExtensionDecl>(decl))
+          if (SM.rangeContainsTokenLoc(ext->getSourceRange(), Loc))
+            ext->computeExtendedNominal();
+    }
   }
 
   // Type-check this context.

test/IDE/complete_type.swift

@@ -765,3 +765,17 @@ func testUnbound2(x: OuterStruct<Int>.Inner.#^UNBOUND_DOT_3^#) {}
 // UNBOUND_DOT_3: Begin completions
 // UNBOUND_DOT_3-DAG: Keyword/None:                       Type[#OuterStruct<Int>.Inner.Type#]; name=Type
 // UNBOUND_DOT_3: End completions
+
+// rdar://problem/67102794
+struct HasProtoAlias {
+  typealias ProtoAlias = FooProtocol
+}
+extension FooStruct: HasProtoAlias.#^EXTENSION_INHERITANCE_1?check=EXTENSION_INHERITANCE^# {}
+
+struct ContainExtension {
+  extension FooStruct: HasProtoAlias.#^EXTENSION_INHERITANCE_2?check=EXTENSION_INHERITANCE^# {}
+}
+// EXTENSION_INHERITANCE: Begin completions, 2 items
+// EXTENSION_INHERITANCE-DAG: Decl[TypeAlias]/CurrNominal:        ProtoAlias[#FooProtocol#];
+// EXTENSION_INHERITANCE-DAG: Keyword/None:                       Type[#HasProtoAlias.Type#];
+// EXTENSION_INHERITANCE: End completions