Merge branch 'nix-repl-e' of https://github.com/zimbatm/nix

2 files changed, 35 insertions, 0 deletions

diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index b0f80db32..06b472d8b 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -93,4 +93,36 @@ Value * findAlongAttrPath(EvalState & state, const string & attrPath,
 }
 
 
+Pos findDerivationFilename(EvalState & state, Value & v, std::string what)
+{
+    Value * v2;
+    try {
+        auto dummyArgs = state.allocBindings(0);
+        v2 = findAlongAttrPath(state, "meta.position", *dummyArgs, v);
+    } catch (Error &) {
+        throw Error("package '%s' has no source location information", what);
+    }
+
+    // FIXME: is it possible to extract the Pos object instead of doing this
+    //        toString + parsing?
+    auto pos = state.forceString(*v2);
+
+    auto colon = pos.rfind(':');
+    if (colon == std::string::npos)
+        throw Error("cannot parse meta.position attribute '%s'", pos);
+
+    std::string filename(pos, 0, colon);
+    unsigned int lineno;
+    try {
+        lineno = std::stoi(std::string(pos, colon + 1));
+    } catch (std::invalid_argument & e) {
+        throw Error("cannot parse line number '%s'", pos);
+    }
+
+    Symbol file = state.symbols.create(filename);
+
+    return { file, lineno, 0 };
+}
+
+
 }
diff --git a/src/libexpr/attr-path.hh b/src/libexpr/attr-path.hh
index 46a341950..716e5ba27 100644
--- a/src/libexpr/attr-path.hh
+++ b/src/libexpr/attr-path.hh
@@ -10,4 +10,7 @@ namespace nix {
 Value * findAlongAttrPath(EvalState & state, const string & attrPath,
     Bindings & autoArgs, Value & vIn);
 
+/* Heuristic to find the filename and lineno or a nix value. */
+Pos findDerivationFilename(EvalState & state, Value & v, std::string what);
+
 }