Cache parse trees

This prevents EvalState::resetFileCache() from parsing everything all
over again.

2 files changed, 19 insertions, 2 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 01658aa25..facfddbb5 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -332,7 +332,6 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
 
 EvalState::~EvalState()
 {
-    fileEvalCache.clear();
 }
 
 
@@ -711,7 +710,17 @@ void EvalState::evalFile(const Path & path_, Value & v)
     }
 
     printTalkative("evaluating file '%1%'", path2);
-    Expr * e = parseExprFromFile(checkSourcePath(path2));
+    Expr * e = nullptr;
+
+    auto j = fileParseCache.find(path2);
+    if (j != fileParseCache.end())
+        e = j->second;
+
+    if (!e)
+        e = parseExprFromFile(checkSourcePath(path2));
+
+    fileParseCache[path2] = e;
+
     try {
         eval(e, v);
     } catch (Error & e) {
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 146f21255..d0f298e16 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -90,6 +90,14 @@ public:
 private:
     SrcToStore srcToStore;
 
+    /* A cache from path names to parse trees. */
+#if HAVE_BOEHMGC
+    typedef std::map<Path, Expr *, std::less<Path>, traceable_allocator<std::pair<const Path, Expr *> > > FileParseCache;
+#else
+    typedef std::map<Path, Expr *> FileParseCache;
+#endif
+    FileParseCache fileParseCache;
+
     /* A cache from path names to values. */
 #if HAVE_BOEHMGC
     typedef std::map<Path, Value, std::less<Path>, traceable_allocator<std::pair<const Path, Value> > > FileEvalCache;