* New primop: abort "error message".

src/libexpr/eval.cc

@@ -515,7 +515,7 @@ Expr evalExpr2(EvalState & state, Expr e)
         try {
             return concatStrings(state, args);
         } catch (Error & e) {
-            e.addPrefix(format("in a string concatenation: "));
+            e.addPrefix(format("in a string concatenation:\n"));
             throw;
         }
     }
@@ -527,7 +527,7 @@ Expr evalExpr2(EvalState & state, Expr e)
             ATermList l2 = evalList(state, e2);
             return makeList(ATconcat(l1, l2));
         } catch (Error & e) {
-            e.addPrefix(format("in a list concatenation: "));
+            e.addPrefix(format("in a list concatenation:\n"));
             throw;
         }
     }

src/libexpr/nixexpr.hh

@@ -11,6 +11,7 @@
 
 MakeError(EvalError, Error)
 MakeError(AssertionError, EvalError)
+MakeError(Abort, EvalError)
 MakeError(TypeError, EvalError)
 
 

src/libexpr/primops.cc

@@ -629,6 +629,13 @@ static Expr primDependencyClosure(EvalState & state, const ATermVector & args)
 }
 
 
+static Expr primAbort(EvalState & state, const ATermVector & args)
+{
+    throw Abort(format("evaluation aborted with the following error message: %1%") %
+        evalString(state, args[0]));
+}
+
+
 /* Apply a function to every element of a list. */
 static Expr primMap(EvalState & state, const ATermVector & args)
 {
@@ -700,6 +707,7 @@ void EvalState::addPrimOps()
     addPrimOp("toString", 1, primToString);
     addPrimOp("isNull", 1, primIsNull);
     addPrimOp("dependencyClosure", 1, primDependencyClosure);
+    addPrimOp("abort", 1, primAbort);
 
     addPrimOp("map", 2, primMap);
     addPrimOp("removeAttrs", 2, primRemoveAttrs);

tests/lang/eval-fail-abort.nix

@@ -0,0 +1 @@
+if true then abort "this should fail" else 1