From 2941a599fa6c9fec5d084cec2cb5da3752efc5f8 Mon Sep 17 00:00:00 2001
From: oxalica <oxalicc@pm.me>
Date: Sun, 26 Mar 2023 22:39:24 +0800
Subject: [PATCH] Catch eval errors in `hasContent`

`legacyPackages` of nixpkgs trigger eval errors in `hasContent`, causing
the whole `legacyPackages` being skipped. We should treat it as
has-content in that case.
---
 src/nix/flake.cc     | 55 +++++++++++++++++++++++++-------------------
 tests/flakes/show.sh | 20 ++++++++++++++++
 2 files changed, 51 insertions(+), 24 deletions(-)

diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 0a6616396..df19e87e4 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -1026,36 +1026,43 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
             auto visitor2 = visitor.getAttr(attrName);
 
-            if ((attrPathS[0] == "apps"
-                    || attrPathS[0] == "checks"
-                    || attrPathS[0] == "devShells"
-                    || attrPathS[0] == "legacyPackages"
-                    || attrPathS[0] == "packages")
-                && (attrPathS.size() == 1 || attrPathS.size() == 2)) {
-                for (const auto &subAttr : visitor2->getAttrs()) {
-                    if (hasContent(*visitor2, attrPath2, subAttr)) {
-                        return true;
+            try {
+                if ((attrPathS[0] == "apps"
+                        || attrPathS[0] == "checks"
+                        || attrPathS[0] == "devShells"
+                        || attrPathS[0] == "legacyPackages"
+                        || attrPathS[0] == "packages")
+                    && (attrPathS.size() == 1 || attrPathS.size() == 2)) {
+                    for (const auto &subAttr : visitor2->getAttrs()) {
+                        if (hasContent(*visitor2, attrPath2, subAttr)) {
+                            return true;
+                        }
                     }
+                    return false;
                 }
-                return false;
-            }
 
-            if ((attrPathS.size() == 1)
-                && (attrPathS[0] == "formatter"
-                    || attrPathS[0] == "nixosConfigurations"
-                    || attrPathS[0] == "nixosModules"
-                    || attrPathS[0] == "overlays"
-                    )) {
-                for (const auto &subAttr : visitor2->getAttrs()) {
-                    if (hasContent(*visitor2, attrPath2, subAttr)) {
-                        return true;
+                if ((attrPathS.size() == 1)
+                    && (attrPathS[0] == "formatter"
+                        || attrPathS[0] == "nixosConfigurations"
+                        || attrPathS[0] == "nixosModules"
+                        || attrPathS[0] == "overlays"
+                        )) {
+                    for (const auto &subAttr : visitor2->getAttrs()) {
+                        if (hasContent(*visitor2, attrPath2, subAttr)) {
+                            return true;
+                        }
                     }
+                    return false;
                 }
-                return false;
-            }
 
-            // If we don't recognize it, it's probably content
-            return true;
+                // 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(
diff --git a/tests/flakes/show.sh b/tests/flakes/show.sh
index dd13264b9..6f886ccfb 100644
--- a/tests/flakes/show.sh
+++ b/tests/flakes/show.sh
@@ -64,3 +64,23 @@ in
 assert show_output == { };
 true
 '
+
+# Test that legacyPackages with errors are handled correctly.
+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
+'