Merge pull request #6663 from Ma27/follows-invalid-input

flakes: throw an error if `follows`-declaration for an input is invalid

src/libexpr/flake/flake.cc

@@ -352,6 +352,39 @@ LockedFlake lockFlake(
 
         std::vector<FlakeRef> parents;
 
+        std::function<void(
+            const InputPath & inputPathPrefix,
+            const FlakeInputs & flakeInputs
+            )>
+            checkFollowsDeclarations;
+
+        checkFollowsDeclarations = [&](
+            const InputPath & inputPathPrefix,
+            const FlakeInputs & flakeInputs
+        ) {
+            for (auto [inputPath, inputOverride] : overrides) {
+                auto inputPath2(inputPath);
+                auto follow = inputPath2.back();
+                inputPath2.pop_back();
+                if (inputPath2 == inputPathPrefix
+                    && flakeInputs.find(follow) == flakeInputs.end()
+                ) {
+                    std::string root;
+                    for (auto & element : inputPath2) {
+                        root.append(element);
+                        if (element != inputPath2.back()) {
+                            root.append(".inputs.");
+                        }
+                    }
+                    warn(
+                        "%s has a `follows'-declaration for a non-existant input %s!",
+                        root,
+                        follow
+                    );
+                }
+            }
+        };
+
         std::function<void(
             const FlakeInputs & flakeInputs,
             std::shared_ptr<Node> node,
@@ -373,6 +406,8 @@ LockedFlake lockFlake(
         {
             debug("computing lock file node '%s'", printInputPath(inputPathPrefix));
 
+            checkFollowsDeclarations(inputPathPrefix, flakeInputs);
+
             /* Get the overrides (i.e. attributes of the form
                'inputs.nixops.inputs.nixpkgs.url = ...'). */
             for (auto & [id, input] : flakeInputs) {

tests/flakes.sh

@@ -801,6 +801,8 @@ nix flake metadata $flakeFollowsA
 
 nix flake update $flakeFollowsA
 
+nix flake lock $flakeFollowsA
+
 oldLock="$(cat "$flakeFollowsA/flake.lock")"
 
 # Ensure that locking twice doesn't change anything
@@ -823,7 +825,6 @@ cat > $flakeFollowsA/flake.nix <<EOF
     inputs = {
         B = {
             url = "path:./flakeB";
-            inputs.nonFlake.follows = "D";
         };
         D.url = "path:./flakeD";
     };
@@ -859,3 +860,21 @@ nix store delete $(nix store add-path $badFlakeDir)
 
 [[ $(nix path-info      $(nix store add-path $flake1Dir)) =~ flake1 ]]
 [[ $(nix path-info path:$(nix store add-path $flake1Dir)) =~ simple ]]
+
+# Non-existant follows causes an error
+
+cat >$flakeFollowsA/flake.nix <<EOF
+{
+    description = "Flake A";
+    inputs.B = {
+        url = "path:./flakeB";
+        inputs.invalid.follows = "D";
+    };
+    inputs.D.url = "path:./flakeD";
+    outputs = { ... }: {};
+}
+EOF
+
+git -C $flakeFollowsA add flake.nix
+
+nix flake lock $flakeFollowsA 2>&1 | grep "warning: B has a \`follows'-declaration for a non-existant input invalid!"