add situations where inheriting docs shouldn't happen

Author: QuietMisdreavus

test/SymbolGraph/Relationships/Synthesized/Inputs/RemoteP.swift

@@ -7,3 +7,8 @@ public protocol P {
 
     func bonusFunc()
 }
+
+public extension P {
+    /// Extra default docs!
+    func extraFunc() {}
+}

test/SymbolGraph/Relationships/Synthesized/RemoteInheritedDocs.swift

@@ -8,13 +8,15 @@
 // RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix BONUS
 // RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix INHERIT
 // RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix LOCAL
+// RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix OVERRIDE
 
 // RUN: %target-swift-symbolgraph-extract -module-name RemoteInheritedDocs -I %t -pretty-print -output-dir %t -skip-inherited-docs
 // RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix SOME
 // RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix OTHER
 // RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix BONUS
 // RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix SKIP
 // RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix LOCAL
+// RUN: %FileCheck %s --input-file %t/RemoteInheritedDocs.symbols.json --check-prefix OVERRIDE
 
 // SOME:           "source": "s:19RemoteInheritedDocs1SV8someFuncyyF"
 // SOME-NEXT:      "target": "s:19RemoteInheritedDocs1SV"
@@ -39,18 +41,31 @@
 
 // LOCAL: Local docs override!
 
+// OVERRIDE-NOT: Extra default docs!
+// OVERRIDE-NOT: Extension override!
+
 import RemoteP
 
 // The `RemoteP.P` protocol has three methods: `someFunc` and `bonusFunc` don't have docs upstream,
 // but `otherFunc` does. Regardless, each one needs a `sourceOrigin` field connecting it to
 // upstream.
 
+// `RemoteP.P` also has an extension with a default implementation for `extraFunc` that does have
+// docs, but overriding it here should prevent those from appearing
+
 public struct S: P {
     public func someFunc() {}
 
     public func otherFunc() {}
 
     /// Local docs override!
     public func bonusFunc() {}
+
+    public func extraFunc() {}
+}
+
+public extension P {
+    /// Extension override!
+    func someFunc() {}
 }