From 55e207b2dc43e426bd0dfbc2065b8853a1fc59b0 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Wed, 31 Mar 2010 16:14:32 +0000
Subject: [PATCH] * Cache parse trees to prevent repeated parsing of imported
 Nix   expressions.

---
 src/libexpr/eval.cc  | 9 ++++++++-
 src/libexpr/eval.hh  | 2 ++
 src/libexpr/parser.y | 6 ------
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 0296afe601..b4156ffec1 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -272,7 +272,14 @@ void EvalState::cloneAttrs(Value & src, Value & dst)
 void EvalState::evalFile(const Path & path, Value & v)
 {
     startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
-    Expr e = parseExprFromFile(*this, path);
+
+    Expr e = parseTrees.get(toATerm(path));
+
+    if (!e) {
+        e = parseExprFromFile(*this, path);
+        parseTrees.set(toATerm(path), e);
+    }
+    
     try {
         eval(e, v);
     } catch (Error & e) {
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index eba97dd737..7369892fbc 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -135,6 +135,8 @@ private:
 
     bool allowUnsafeEquality;
 
+    ATermMap parseTrees;
+
 public:
     
     EvalState();
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 2f0c9db3f3..3a56c2627c 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -526,12 +526,6 @@ Expr parseExprFromFile(EvalState & state, Path path)
 {
     assert(path[0] == '/');
 
-#if 0
-    /* Perhaps this is already an imploded parse tree? */
-    Expr e = ATreadFromNamedFile(path.c_str());
-    if (e) return e;
-#endif
-
     /* If `path' is a symlink, follow it.  This is so that relative
        path references work. */
     struct stat st;