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.

2 files changed, 23 insertions, 0 deletions

diff --git a/tests/lang/eval-okay-context-introspection.exp b/tests/lang/eval-okay-context-introspection.exp
new file mode 100644
index 000000000000..27ba77ddaf61
--- /dev/null
+++ b/tests/lang/eval-okay-context-introspection.exp
@@ -0,0 +1 @@
+true
diff --git a/tests/lang/eval-okay-context-introspection.nix b/tests/lang/eval-okay-context-introspection.nix
new file mode 100644
index 000000000000..d9b2ea354990
--- /dev/null
+++ b/tests/lang/eval-okay-context-introspection.nix
@@ -0,0 +1,22 @@
+let
+  drv = derivation {
+    name = "fail";
+    builder = "/bin/false";
+    system = "x86_64-linux";
+    outputs = [ "out" "foo" ];
+  };
+
+  path = "${./eval-okay-context-introspection.nix}";
+
+  desired-context = {
+    "${builtins.unsafeDiscardStringContext path}" = {
+      path = true;
+    };
+    "${builtins.unsafeDiscardStringContext drv.drvPath}" = {
+      outputs = [ "foo" "out" ];
+      allOutputs = true;
+    };
+  };
+
+  legit-context = "${path}${drv.outPath}${drv.foo.outPath}${drv.drvPath}";
+in builtins.getContext legit-context == desired-context