From 75837651f15fc3c451ae54afbb5927c1abe329c5 Mon Sep 17 00:00:00 2001
From: Iwan Aucamp <aucampia@gmail.com>
Date: Fri, 31 Jul 2015 17:32:25 +0200
Subject: [PATCH] Output line number on infinite recursion

---
 src/libexpr/eval-inline.hh |  9 +++++----
 src/libexpr/eval.cc        | 16 ++++++++--------
 src/libexpr/eval.hh        |  2 +-
 tests/misc.sh              |  3 +++
 4 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/src/libexpr/eval-inline.hh b/src/libexpr/eval-inline.hh
index 178e06c80..4abc485aa 100644
--- a/src/libexpr/eval-inline.hh
+++ b/src/libexpr/eval-inline.hh
@@ -1,15 +1,16 @@
 #pragma once
 
 #include "eval.hh"
+#include "shared.hh"
 
 #define LocalNoInline(f) static f __attribute__((noinline)); f
 #define LocalNoInlineNoReturn(f) static f __attribute__((noinline, noreturn)); f
 
 namespace nix {
 
-LocalNoInlineNoReturn(void throwEvalError(const char * s))
+LocalNoInlineNoReturn(void throwEvalError(const FormatOrString & fs))
 {
-    throw EvalError(s);
+    throw EvalError(fs);
 }
 
 LocalNoInlineNoReturn(void throwTypeError(const char * s, const Value & v))
@@ -24,7 +25,7 @@ LocalNoInlineNoReturn(void throwTypeError(const char * s, const Value & v, const
 }
 
 
-void EvalState::forceValue(Value & v)
+void EvalState::forceValue(Value & v, const Pos & pos)
 {
     if (v.type == tThunk) {
         Env * env = v.thunk.env;
@@ -43,7 +44,7 @@ void EvalState::forceValue(Value & v)
     else if (v.type == tApp)
         callFunction(*v.app.left, *v.app.right, v, noPos);
     else if (v.type == tBlackhole)
-        throwEvalError("infinite recursion encountered");
+        throwEvalError(format("infinite recursion encountered, at %1%") % pos);
 }
 
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 769aae0a9..ec02e61b0 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -746,7 +746,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
     for (auto & i : dynamicAttrs) {
         Value nameVal;
         i.nameExpr->eval(state, *dynamicEnv, nameVal);
-        state.forceValue(nameVal);
+        state.forceValue(nameVal, i.pos);
         if (nameVal.type == tNull)
             continue;
         state.forceStringNoCtx(nameVal);
@@ -792,7 +792,7 @@ void ExprList::eval(EvalState & state, Env & env, Value & v)
 void ExprVar::eval(EvalState & state, Env & env, Value & v)
 {
     Value * v2 = state.lookupVar(&env, *this, false);
-    state.forceValue(*v2);
+    state.forceValue(*v2, pos);
     v = *v2;
 }
 
@@ -831,7 +831,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
             Bindings::iterator j;
             Symbol name = getName(i, state, env);
             if (def) {
-                state.forceValue(*vAttrs);
+                state.forceValue(*vAttrs, pos);
                 if (vAttrs->type != tAttrs ||
                     (j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
                 {
@@ -848,7 +848,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
             if (state.countCalls && pos2) state.attrSelects[*pos2]++;
         }
 
-        state.forceValue(*vAttrs);
+        state.forceValue(*vAttrs, ( pos2 != NULL ? *pos2 : this->pos ) );
 
     } catch (Error & e) {
         if (pos2 && pos2->file != state.sDerivationNix)
@@ -950,10 +950,10 @@ void EvalState::callFunction(Value & fun, Value & arg, Value & v, const Pos & po
     if (fun.type == tAttrs) {
       auto found = fun.attrs->find(sFunctor);
       if (found != fun.attrs->end()) {
-        forceValue(*found->value);
+        forceValue(*found->value, pos);
         Value * v2 = allocValue();
         callFunction(*found->value, fun, *v2, pos);
-        forceValue(*v2);
+        forceValue(*v2, pos);
         return callFunction(*v2, arg, v, pos);
       }
     }
@@ -1280,7 +1280,7 @@ void EvalState::forceValueDeep(Value & v)
 
 NixInt EvalState::forceInt(Value & v, const Pos & pos)
 {
-    forceValue(v);
+    forceValue(v, pos);
     if (v.type != tInt)
         throwTypeError("value is %1% while an integer was expected, at %2%", v, pos);
     return v.integer;
@@ -1306,7 +1306,7 @@ void EvalState::forceFunction(Value & v, const Pos & pos)
 
 string EvalState::forceString(Value & v, const Pos & pos)
 {
-    forceValue(v);
+    forceValue(v, pos);
     if (v.type != tString) {
         if (pos)
             throwTypeError("value is %1% while a string was expected, at %2%", v, pos);
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 74a273b54..8df0084fd 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -136,7 +136,7 @@ public:
        of the evaluation of the thunk.  If `v' is a delayed function
        application, call the function and overwrite `v' with the
        result.  Otherwise, this is a no-op. */
-    inline void forceValue(Value & v);
+    inline void forceValue(Value & v, const Pos & pos = noPos);
 
     /* Force a value, then recursively force list elements and
        attributes. */
diff --git a/tests/misc.sh b/tests/misc.sh
index 1b4d8f2cf..6d0ab3adc 100644
--- a/tests/misc.sh
+++ b/tests/misc.sh
@@ -14,3 +14,6 @@ nix-env --version | grep "$version"
 # Usage errors.
 nix-env --foo 2>&1 | grep "no operation"
 nix-env -q --foo 2>&1 | grep "unknown flag"
+
+# Eval Errors.
+nix-instantiate --eval -E 'let a = {} // a; in a.foo' 2>&1 | grep "infinite recursion encountered, at (string):1:15$"