Add builtins.getContext.

This can be very helpful when debugging, as well as enabling complex
black magic like surgically removing a single dependency from a
string's context.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index d0f298e168..9fe3878916 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -316,6 +316,9 @@ private:
 /* Return a string representing the type of the value `v'. */
 string showType(const Value & v);
 
+/* Decode a context string ‘!<name>!<path>’ into a pair <path,
+   name>. */
+std::pair<string, string> decodeContext(const string & s);
 
 /* If `path' refers to a directory, then append "/default.nix". */
 Path resolveExprPath(Path path);