[SourceKit] Add optional declarations array to interface gen request (#75802)

Introduces the new DeclarationsArrayBuilder and adds it to the
EditorConsumer. Declaration info always includes a kind, offset, and
length, and includes a USR where applicable.
As the USR is already available for editor.open.interface type requests,
this doesn't compute any new information, it just exposes more of what's
there already.

tools/SourceKit/lib/SwiftLang/SwiftEditorInterfaceGen.cpp

@@ -56,6 +56,8 @@ public:
     const Decl *Dcl = nullptr;
     /// The range in the interface source.
     TextRange Range;
+    /// The USR, if the declaration has one
+    StringRef USR;
 
     TextDecl(const Decl *D, TextRange Range)
       : Dcl(D), Range(Range) {}
@@ -66,6 +68,8 @@ public:
     std::string Text;
     std::vector<TextReference> References;
     std::vector<TextDecl> Decls;
+    /// Do not clear the map or erase elements,
+    /// without keeping the Decls vector in sync
     llvm::StringMap<TextDecl> USRMap;
   };
 
@@ -155,8 +159,17 @@ public:
           OS << TargetUSR;
         }
         StringRef USR = OS.str();
-        Info.USRMap[USR] = Entry;
         DeclUSRs.emplace_back(VD, USR);
+        auto iterator = Info.USRMap.insert_or_assign(USR, Entry).first;
+        // Set the USR in the declarations to the key in the USRMap, because the
+        // lifetime of that matches/exceeds the lifetime of Decls. String keys
+        // in the StringMap are heap allocated and only get destroyed on
+        // explicit erase() or clear() calls, or on destructor calls (the
+        // Programmer's Manual description itself also states that StringMap
+        // "only ever copies a string if a value is inserted").
+        // Thus this never results in a dangling reference, as the USRMap is
+        // never cleared and no elements are erased in its lifetime.
+        Info.Decls.back().USR = iterator->getKey();
       }
     }
   }
@@ -265,6 +278,21 @@ static void reportSemanticAnnotations(const SourceTextInfo &IFaceInfo,
   }
 }
 
+/// Create the declarations array (sourcekitd::DeclarationsArrayBuilder) from
+/// the SourceTextInfo about declarations
+static void reportDeclarations(const SourceTextInfo &IFaceInfo,
+                               EditorConsumer &Consumer) {
+  for (auto &Dcl : IFaceInfo.Decls) {
+    if (!Dcl.Dcl)
+      continue;
+    UIdent Kind = SwiftLangSupport::getUIDForDecl(Dcl.Dcl);
+    if (Kind.isInvalid())
+      continue;
+    Consumer.handleDeclaration(Dcl.Range.Offset, Dcl.Range.Length, Kind,
+                               Dcl.USR);
+  }
+}
+
 namespace {
 /// A diagnostic consumer that picks up module loading errors.
 class ModuleLoadingErrorConsumer final : public DiagnosticConsumer {
@@ -593,6 +621,8 @@ void SwiftInterfaceGenContext::reportEditorInfo(EditorConsumer &Consumer) const
   reportSyntacticAnnotations(Impl.TextCI, Consumer);
   reportDocumentStructure(Impl.TextCI, Consumer);
   reportSemanticAnnotations(Impl.Info, Consumer);
+
+  reportDeclarations(Impl.Info, Consumer);
   Consumer.finished();
 }