allow constants in systemlib

The problem was a few:

* All constant declarations were wrapped in a statement list. The merge-only check was allowing top-level `define()`s but not top level statement lists. I unwrapped them. I have no idea why it was done. Probalby just cargo cult programming.
* When converting a UnitEmitter to a Unit we only allowed constants in RepoAuthoritative mode and not systemlib mode.
* Systemlib constants weren't being set as UnitMergeKindPersistentDefine
* UnitMergeKindPersistentDefine constants weren't being marked mergeOnly when pulling out of a repro

hphp/compiler/expression/simple_function_call.cpp

@@ -635,7 +635,7 @@ bool SimpleFunctionCall::isDefineWithoutImpl(AnalysisResultConstPtr ar) {
     if (!name) return false;
     string varName = name->getIdentifier();
     if (varName.empty()) return false;
-    if (ar->isSystemConstant(varName)) {
+    if (!SystemLib::s_inited || ar->isSystemConstant(varName)) {
       always_assert(!m_extra);
       return true;
     }

hphp/runtime/vm/unit.cpp

@@ -1986,20 +1986,24 @@ void UnitRepoProxy::GetUnitMergeablesStmt
   do {
     query.step();
     if (query.row()) {
+      int mergeableIx;           /**/ query.getInt(0, mergeableIx);
+      int mergeableKind;         /**/ query.getInt(1, mergeableKind);
+      Id mergeableId;            /**/ query.getInt(2, mergeableId);
+
       if (UNLIKELY(!RuntimeOption::RepoAuthoritative)) {
         /*
          * We're using a repo generated in WholeProgram mode,
          * but we're not using it in RepoAuthoritative mode
          * (this is dodgy to start with). We're not going to
          * deal with requires at merge time, so drop them
-         * here, and clear the mergeOnly flag for the unit
+         * here, and clear the mergeOnly flag for the unit.
+         * The one exception is persistent constants are allowed in systemlib.
          */
-        ue.setMergeOnly(false);
-        break;
+        if (mergeableKind != UnitMergeKindPersistentDefine ||
+           SystemLib::s_inited) {
+          ue.setMergeOnly(false);
+        }
       }
-      int mergeableIx;           /**/ query.getInt(0, mergeableIx);
-      int mergeableKind;         /**/ query.getInt(1, mergeableKind);
-      Id mergeableId;            /**/ query.getInt(2, mergeableId);
       switch (mergeableKind) {
         case UnitMergeKindReqDoc:
           ue.insertMergeableInclude(mergeableIx,
@@ -2583,7 +2587,7 @@ Unit* UnitEmitter::create() {
     for (MergeableStmtVec::const_iterator it = m_mergeableStmts.begin();
          it != m_mergeableStmts.end(); ++it) {
       extra++;
-      if (!RuntimeOption::RepoAuthoritative) {
+      if (!RuntimeOption::RepoAuthoritative && SystemLib::s_inited) {
         if (it->first != UnitMergeKindClass) {
           extra = 0;
           u->m_mergeOnly = false;
@@ -2640,9 +2644,9 @@ Unit* UnitEmitter::create() {
           break;
         }
         case UnitMergeKindDefine:
-        case UnitMergeKindPersistentDefine:
-        case UnitMergeKindGlobal: {
+        case UnitMergeKindGlobal:
           assert(RuntimeOption::RepoAuthoritative);
+        case UnitMergeKindPersistentDefine: {
           void* name = u->lookupLitstrId(m_mergeableValues[it->second].first);
           mi->mergeableObj(ix++) = (char*)name + (int)it->first;
           auto& tv = m_mergeableValues[it->second].second;

hphp/util/parser/hphp.y

@@ -126,22 +126,15 @@ static void scalar_null(Parser *_p, Token &out) {
 ///////////////////////////////////////////////////////////////////////////////
 // converting constant declartion to "define(name, value);"
 
-static void on_constant(Parser *_p, Token &out, Token *stmts,
-                        Token &name, Token &value) {
+static void on_constant(Parser *_p, Token &out, Token &name, Token &value) {
   Token sname;   _p->onScalar(sname, T_CONSTANT_ENCAPSED_STRING, name);
 
   Token fname;   fname.setText("define");
   Token params1; _p->onCallParam(params1, NULL, sname, 0);
   Token params2; _p->onCallParam(params2, &params1, value, 0);
   Token call;    _p->onCall(call, 0, fname, params2, 0);
-  Token scall;   _p->onExpStatement(scall, call);
-
-  Token stmts0;
-  if (!stmts) {
-    _p->onStatementListStart(stmts0);
-    stmts = &stmts0;
-  }
-  _p->addStatement(out, *stmts, scall);
+  
+  _p->onExpStatement(out, call);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -898,10 +891,10 @@ constant_declaration:
     constant_declaration ','
     hh_name_with_type
     '=' static_scalar                  { $3.setText(_p->nsDecl($3.text()));
-                                         on_constant(_p,$$,&$1,$3,$5);}
+                                         on_constant(_p,$$,$3,$5);}
   | T_CONST hh_name_with_type '='
     static_scalar                      { $2.setText(_p->nsDecl($2.text()));
-                                         on_constant(_p,$$,  0,$2,$4);}
+                                         on_constant(_p,$$,$2,$4);}
 ;
 
 inner_statement_list: