populate: fail on inputs drawn that the flake doesn't have

Nix ignores an input that --override-input names but the flake doesn't
have, with a warning, so a misspelt input name in inputs draws nothing,
and the source keeps using its own input.

Before changing anything, populate locks the flake of each source that
draws inputs, with an empty flake in place of each input drawn, which
may be unreachable, and fails, naming the source and the input, unless
the flake has each input drawn.  Below an input drawn from a source, the
path continues in the flake of that source.

An edge case misspells an input of the source's flake, and one below an
input drawn from a source, both ways of drawing inputs.

1 files changed, 24 insertions, 0 deletions

diff --git a/tests/scenarios.nix b/tests/scenarios.nix
index 89a3b09..e23d14e 100644
--- a/tests/scenarios.nix
+++ b/tests/scenarios.nix
@@ -1445,6 +1445,30 @@ assert !(krops.isLocalTarget (targets.remote "/"));
         '';
       }];
     })
+    # Misspelt input names draw nothing, so they fail before anything
+    # changes: of the source's flake, and below an input drawn from a source.
+    (modes "inputs-typo" ({ draw, ... }: {
+      phases = [
+        {
+          sources = alt // {
+            x.flake-input = {
+              url = "/fixtures/top"; name = "dep"; inherit fetchOnTarget;
+            } // draw { innr.follows = "alt"; };
+          };
+          expect.fail = "error: source x draws input innr from source alt, but its flake has no input innr";
+        }
+        {
+          sources = {
+            x.flake = {
+              url = "/fixtures/top"; inherit fetchOnTarget;
+            } // draw { dep = { follows = "b"; inputs.qq.follows = "c2"; }; };
+            b.file = "/fixtures/two";
+            c2.file = "/fixtures/c2";
+          };
+          expect.fail = "error: source x draws input dep/qq from source c2, but the flake of source b has no input qq";
+        }
+      ];
+    }))
     # A signal ending populate leaves neither the ssh master nor the
     # temporary directory.
     (s "interrupt" {