Alias traceable_allocator to std::allocator when building without GC

This allows us to get rid of a bunch of #ifdefs.

src/libcmd/command.cc

@@ -127,14 +127,9 @@ ref<EvalState> EvalCommand::getEvalState()
 {
     if (!evalState) {
         evalState =
-            #if HAVE_BOEHMGC
             std::allocate_shared<EvalState>(
                 traceable_allocator<EvalState>(),
-            #else
-            std::make_shared<EvalState>(
-            #endif
-                lookupPath, getEvalStore(), fetchSettings, evalSettings, getStore())
-            ;
+                lookupPath, getEvalStore(), fetchSettings, evalSettings, getStore());
 
         evalState->repair = repair;
 

src/libexpr/eval.cc

@@ -99,11 +99,7 @@ static const char * makeImmutableString(std::string_view s)
 
 RootValue allocRootValue(Value * v)
 {
-#if HAVE_BOEHMGC
     return std::allocate_shared<Value *>(traceable_allocator<Value *>(), v);
-#else
-    return std::make_shared<Value *>(v);
-#endif
 }
 
 // Pretty print types for assertion errors

src/libexpr/eval.hh

@@ -139,11 +139,7 @@ struct Constant
     bool impureOnly = false;
 };
 
-#if HAVE_BOEHMGC
 typedef std::map<std::string, Value *, std::less<std::string>, traceable_allocator<std::pair<const std::string, Value *> > > ValMap;
-#else
-    typedef std::map<std::string, Value *> ValMap;
-#endif
 
 typedef std::unordered_map<PosIdx, DocComment> DocCommentMap;
 
@@ -329,21 +325,13 @@ private:
     /**
      * A cache from path names to parse trees.
      */
-#if HAVE_BOEHMGC
     typedef std::unordered_map<SourcePath, Expr *, std::hash<SourcePath>, std::equal_to<SourcePath>, traceable_allocator<std::pair<const SourcePath, Expr *>>> FileParseCache;
-#else
-    typedef std::unordered_map<SourcePath, Expr *> FileParseCache;
-#endif
     FileParseCache fileParseCache;
 
     /**
      * A cache from path names to values.
      */
-#if HAVE_BOEHMGC
     typedef std::unordered_map<SourcePath, Value, std::hash<SourcePath>, std::equal_to<SourcePath>, traceable_allocator<std::pair<const SourcePath, Value>>> FileEvalCache;
-#else
-    typedef std::unordered_map<SourcePath, Value> FileEvalCache;
-#endif
     FileEvalCache fileEvalCache;
 
     /**

src/libexpr/gc-small-vector.hh

@@ -2,28 +2,15 @@
 
 #include <boost/container/small_vector.hpp>
 
-#if HAVE_BOEHMGC
-
-#include <gc/gc.h>
-#include <gc/gc_cpp.h>
-#include <gc/gc_allocator.h>
-
-#endif
+#include "value.hh"
 
 namespace nix {
 
-struct Value;
-
 /**
  * A GC compatible vector that may used a reserved portion of `nItems` on the stack instead of allocating on the heap.
  */
-#if HAVE_BOEHMGC
 template <typename T, size_t nItems>
 using SmallVector = boost::container::small_vector<T, nItems, traceable_allocator<T>>;
-#else
-template <typename T, size_t nItems>
-using SmallVector = boost::container::small_vector<T, nItems>;
-#endif
 
 /**
  * A vector of value pointers. See `SmallVector`.

src/libexpr/get-drvs.hh

@@ -83,11 +83,7 @@ public:
 };
 
 
-#if HAVE_BOEHMGC
 typedef std::list<PackageInfo, traceable_allocator<PackageInfo>> PackageInfos;
-#else
-typedef std::list<PackageInfo> PackageInfos;
-#endif
 
 
 /**

src/libexpr/primops.cc

@@ -3136,11 +3136,7 @@ static void prim_zipAttrsWith(EvalState & state, const PosIdx pos, Value * * arg
         std::optional<ListBuilder> list;
     };
 
-#if HAVE_BOEHMGC
     std::map<Symbol, Item, std::less<Symbol>, traceable_allocator<std::pair<const Symbol, Item>>> attrsSeen;
-#else
-    std::map<Symbol, Item> attrsSeen;
-#endif
 
     state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.zipAttrsWith");
     state.forceList(*args[1], pos, "while evaluating the second argument passed to builtins.zipAttrsWith");

src/libexpr/value.hh

@@ -12,7 +12,11 @@
 
 #if HAVE_BOEHMGC
 #include <gc/gc_allocator.h>
+#else
+template<typename T>
+using traceable_allocator = std::allocator<T>;
 #endif
+
 #include <nlohmann/json_fwd.hpp>
 
 namespace nix {
@@ -498,15 +502,9 @@ void Value::mkBlackhole()
 }
 
 
-#if HAVE_BOEHMGC
 typedef std::vector<Value *, traceable_allocator<Value *>> ValueVector;
 typedef std::unordered_map<Symbol, Value *, std::hash<Symbol>, std::equal_to<Symbol>, traceable_allocator<std::pair<const Symbol, Value *>>> ValueMap;
 typedef std::map<Symbol, ValueVector, std::less<Symbol>, traceable_allocator<std::pair<const Symbol, ValueVector>>> ValueVectorMap;
-#else
-typedef std::vector<Value *> ValueVector;
-typedef std::unordered_map<Symbol, Value *> ValueMap;
-typedef std::map<Symbol, ValueVector> ValueVectorMap;
-#endif
 
 
 /**