Merge pull request #8109 from oxalica/fix/show-legacy-packages

Catch eval errors in `hasContent`

src/nix/flake.cc

@@ -1026,6 +1026,7 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
             auto visitor2 = visitor.getAttr(attrName);
 
+            try {
                 if ((attrPathS[0] == "apps"
                         || attrPathS[0] == "checks"
                         || attrPathS[0] == "devShells"
@@ -1056,6 +1057,12 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
                 // If we don't recognize it, it's probably content
                 return true;
+            } catch (EvalError & e) {
+                // Some attrs may contain errors, eg. legacyPackages of
+                // nixpkgs. We still want to recurse into it, instead of
+                // skipping it at all.
+                return true;
+            }
         };
 
         std::function<nlohmann::json(

tests/flakes/show.sh

@@ -64,3 +64,24 @@ in
 assert show_output == { };
 true
 '
+
+# Test that attributes with errors are handled correctly.
+# nixpkgs.legacyPackages is a particularly prominent instance of this.
+cat >flake.nix <<EOF
+{
+  outputs = inputs: {
+    legacyPackages.$system = {
+      AAAAAASomeThingsFailToEvaluate = throw "nooo";
+      simple = import ./simple.nix;
+    };
+  };
+}
+EOF
+nix flake show --json --legacy --all-systems > show-output.json
+nix eval --impure --expr '
+let show_output = builtins.fromJSON (builtins.readFile ./show-output.json);
+in
+assert show_output.legacyPackages.${builtins.currentSystem}.AAAAAASomeThingsFailToEvaluate == { };
+assert show_output.legacyPackages.${builtins.currentSystem}.simple.name == "simple";
+true
+'