add @_nodoc attribute to drop a symbol from the symbol graph

rdar://79049241

Author: QuietMisdreavus

docs/ReferenceGuides/UnderscoredAttributes.md

@@ -482,6 +482,13 @@ Fun fact: Rust has a very similar concept called
 including one called `Send`,
 which inspired the design of `Sendable`.
 
+## `@_nodoc`
+
+Indicates that a declaration should not be included in symbol graphs. Symbols
+marked with this attribute are treated as if they were given an underscored
+name, meaning they are still included in a symbol graph with a "minimum access
+level" of `internal` or lower.
+
 ## `@_nonEphemeral`
 
 Marks a function parameter that cannot accept a temporary pointer produced from

include/swift/AST/Attr.def

@@ -745,6 +745,11 @@ SIMPLE_DECL_ATTR(_alwaysEmitConformanceMetadata, AlwaysEmitConformanceMetadata,
   OnProtocol | UserInaccessible | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
   132)
 
+SIMPLE_DECL_ATTR(_nodoc, NoDoc,
+  OnAnyDecl |
+  APIBreakingToAdd | APIStableToRemove | ABIStableToAdd | ABIStableToRemove,
+  132)
+
 // If you're adding a new underscored attribute here, please document it in
 // docs/ReferenceGuides/UnderscoredAttributes.md.
 

lib/Sema/TypeCheckAttr.cpp

@@ -157,6 +157,7 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   IGNORED_ATTR(Isolated)
   IGNORED_ATTR(Preconcurrency)
   IGNORED_ATTR(BackDeploy)
+  IGNORED_ATTR(NoDoc)
 #undef IGNORED_ATTR
 
   void visitAlignmentAttr(AlignmentAttr *attr) {

lib/Sema/TypeCheckDeclOverride.cpp

@@ -1519,6 +1519,7 @@ namespace  {
     UNINTERESTING_ATTR(Lazy)
     UNINTERESTING_ATTR(LLDBDebuggerFunction)
     UNINTERESTING_ATTR(Mutating)
+    UNINTERESTING_ATTR(NoDoc)
     UNINTERESTING_ATTR(NonMutating)
     UNINTERESTING_ATTR(NonEphemeral)
     UNINTERESTING_ATTR(NonObjC)

lib/SymbolGraphGen/SymbolGraph.cpp

@@ -582,7 +582,7 @@ bool SymbolGraph::isImplicitlyPrivate(const Decl *D,
   }
 
   // Don't record effectively internal declarations if specified
-  if (D->hasUnderscoredNaming()) {
+  if (D->hasUnderscoredNaming() || D->getAttrs().hasAttribute<NoDocAttr>()) {
     // Some implicit decls from Clang with underscored names sneak in, so throw those out
     if (const auto *clangD = D->getClangDecl()) {
       if (clangD->isImplicit())

test/SymbolGraph/Symbols/NoDocAttribute.swift

@@ -0,0 +1,36 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -module-name NoDocAttribute -emit-module -emit-module-path %t/
+// RUN: %target-swift-symbolgraph-extract -module-name NoDocAttribute -I %t -pretty-print -output-dir %t
+// RUN: %FileCheck %s --input-file %t/NoDocAttribute.symbols.json --check-prefix PUBLIC
+
+// RUN: %target-swift-symbolgraph-extract -module-name NoDocAttribute -I %t -pretty-print -output-dir %t -minimum-access-level internal
+// RUN: %FileCheck %s --input-file %t/NoDocAttribute.symbols.json --check-prefix INTERNAL
+
+// RUN: %target-swift-symbolgraph-extract -module-name NoDocAttribute -I %t -pretty-print -output-dir %t -minimum-access-level private
+// RUN: %FileCheck %s --input-file %t/NoDocAttribute.symbols.json --check-prefix PRIVATE
+
+// This test is a mirror of SkipsPublicUnderscore.swift, but using `@_nodoc`
+// instead of underscored names.
+
+public protocol PublicProtocol {}
+
+// PUBLIC-NOT: ShouldntAppear
+// INTERNAL-DAG: ShouldntAppear
+// PRIVATE-DAG: ShouldntAppear
+
+@_nodoc public struct ShouldntAppear: PublicProtocol {
+    public struct InnerShouldntAppear {}
+}
+
+public class SomeClass {
+    // PUBLIC-NOT: internalVar
+    // INTERNAL-NOT: internalVar
+    // PRIVATE-DAG: internalVar
+    @_nodoc internal var internalVar: String = ""
+}
+
+@_nodoc public protocol ProtocolShouldntAppear {}
+
+public struct PublicStruct: ProtocolShouldntAppear {
+    @_nodoc public struct InnerShouldntAppear {}
+}