Drop the dependency on libgc in libmain

Instead, libexpr now depends on libgc.  This means commands like
nix-store that don't do any evaluation no longer require libgc.

src/libexpr/Makefile.new

@@ -9,6 +9,11 @@ libexpr_SOURCES = \
 
 libexpr_LIBS = libutil libstore libformat
 
+# The dependency on libgc must be propagated (i.e. meaning that
+# programs/libraries that use libexpr must explicitly pass -lgc),
+# because inline functions in libexpr's header files call libgc.
+libexpr_LDFLAGS_PROPAGATED = $(BDW_GC_LIBS)
+
 $(d)/parser-tab.cc $(d)/parser-tab.hh: $(d)/parser.y
 	bison -v -o $(libexpr_DIR)/parser-tab.cc $< -d
 

src/libexpr/eval.cc

@@ -129,6 +129,14 @@ string showType(const Value & v)
 }
 
 
+/* Called when the Boehm GC runs out of memory. */
+static void * oomHandler(size_t requested)
+{
+    /* Convert this to a proper C++ exception. */
+    throw std::bad_alloc();
+}
+
+
 EvalState::EvalState()
     : sWith(symbols.create("<with>"))
     , sOutPath(symbols.create("outPath"))
@@ -158,6 +166,14 @@ EvalState::EvalState()
 #if HAVE_BOEHMGC
     static bool gcInitialised = false;
     if (!gcInitialised) {
+
+        /* Initialise the Boehm garbage collector.  This isn't
+           necessary on most platforms, but for portability we do it
+           anyway. */
+        GC_INIT();
+
+        GC_oom_fn = oomHandler;
+
         /* Set the initial heap size to something fairly big (25% of
            physical RAM, up to a maximum of 384 MiB) so that in most
            cases we don't need to garbage collect at all.  (Collection
@@ -181,6 +197,7 @@ EvalState::EvalState()
             debug(format("setting initial heap size to %1% bytes") % size);
             GC_expand_hp(size);
         }
+
         gcInitialised = true;
     }
 #endif

src/libmain/Makefile.new

@@ -5,5 +5,3 @@ libmain_DIR := $(d)
 libmain_SOURCES = shared.cc stack.cc
 
 libmain_LIBS = libstore libutil libformat
-
-libmain_LDFLAGS_PROPAGATED = $(BDW_GC_LIBS)

src/libmain/shared.cc

@@ -15,10 +15,6 @@
 #include <unistd.h>
 #include <signal.h>
 
-#if HAVE_BOEHMGC
-#include <gc/gc.h>
-#endif
-
 
 namespace nix {
 
@@ -231,14 +227,6 @@ static void initAndRun(int argc, char * * argv)
 }
 
 
-/* Called when the Boehm GC runs out of memory. */
-static void * oomHandler(size_t requested)
-{
-    /* Convert this to a proper C++ exception. */
-    throw std::bad_alloc();
-}
-
-
 void showManPage(const string & name)
 {
     string cmd = "man " + name;
@@ -268,14 +256,6 @@ int main(int argc, char * * argv)
 
     std::ios::sync_with_stdio(false);
 
-#if HAVE_BOEHMGC
-    /* Initialise the Boehm garbage collector.  This isn't necessary
-       on most platforms, but for portability we do it anyway. */
-    GC_INIT();
-
-    GC_oom_fn = oomHandler;
-#endif
-
     try {
         try {
             initAndRun(argc, argv);