From b62d36963c45ccaebb328fceaf0bb40f9c02a14b Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Fri, 4 Apr 2014 18:58:15 +0200
Subject: [PATCH] forceInt: Show position info

---
 src/libexpr/eval.cc    |  4 ++--
 src/libexpr/eval.hh    |  2 +-
 src/libexpr/primops.cc | 16 ++++++++--------
 3 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 3a2a84916..0be1e7349 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1151,11 +1151,11 @@ void EvalState::strictForceValue(Value & v)
 }
 
 
-NixInt EvalState::forceInt(Value & v)
+NixInt EvalState::forceInt(Value & v, const Pos & pos)
 {
     forceValue(v);
     if (v.type != tInt)
-        throwTypeError("value is %1% while an integer was expected", v);
+        throwTypeError("value is %1% while an integer was expected, at %2%", v, pos);
     return v.integer;
 }
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index e69b8455e..0a424ddb9 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -158,7 +158,7 @@ public:
     void strictForceValue(Value & v);
 
     /* Force `v', and then verify that it has the expected type. */
-    NixInt forceInt(Value & v);
+    NixInt forceInt(Value & v, const Pos & pos);
     bool forceBool(Value & v);
     inline void forceAttrs(Value & v);
     inline void forceList(Value & v);
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 403edefab..b33b76bca 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -954,7 +954,7 @@ static void elemAt(EvalState & state, const Pos & pos, Value & list, int n, Valu
 /* Return the n-1'th element of a list. */
 static void prim_elemAt(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    elemAt(state, pos, *args[0], state.forceInt(*args[1]), v);
+    elemAt(state, pos, *args[0], state.forceInt(*args[1], pos), v);
 }
 
 
@@ -1061,27 +1061,27 @@ static void prim_length(EvalState & state, const Pos & pos, Value * * args, Valu
 
 static void prim_add(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    mkInt(v, state.forceInt(*args[0]) + state.forceInt(*args[1]));
+    mkInt(v, state.forceInt(*args[0], pos) + state.forceInt(*args[1], pos));
 }
 
 
 static void prim_sub(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    mkInt(v, state.forceInt(*args[0]) - state.forceInt(*args[1]));
+    mkInt(v, state.forceInt(*args[0], pos) - state.forceInt(*args[1], pos));
 }
 
 
 static void prim_mul(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    mkInt(v, state.forceInt(*args[0]) * state.forceInt(*args[1]));
+    mkInt(v, state.forceInt(*args[0], pos) * state.forceInt(*args[1], pos));
 }
 
 
 static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    NixInt i2 = state.forceInt(*args[1]);
+    NixInt i2 = state.forceInt(*args[1], pos);
     if (i2 == 0) throw EvalError(format("division by zero, at %1%") % pos);
-    mkInt(v, state.forceInt(*args[0]) / i2);
+    mkInt(v, state.forceInt(*args[0], pos) / i2);
 }
 
 
@@ -1116,8 +1116,8 @@ static void prim_toString(EvalState & state, const Pos & pos, Value * * args, Va
    non-negative. */
 static void prim_substring(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    int start = state.forceInt(*args[0]);
-    int len = state.forceInt(*args[1]);
+    int start = state.forceInt(*args[0], pos);
+    int len = state.forceInt(*args[1], pos);
     PathSet context;
     string s = state.coerceToString(*args[2], context);