stdenv: allow querying meta on disallowed packages

In the end I've chosen to do the check when evaluating the name.
There were two tricky points to consider:
 - nix-env -qa (changes in there tend to be very slow to get released)
 - hydra.nixos.org
   #9305 (comment)

lib/check-meta.nix

@@ -2,17 +2,28 @@ let
   lib = import ./default.nix;
 in rec {
 
-  # Extend a derivation with a check for brokenness, license, etc.
-  # Throw a descriptive error when the check fails.
-  # Note: no dependencies are checked in this step.
-  addMetaCheck = config: meta: drv:
+  # Extend attributes to be passed to derivation (or similar) with a check
+  # for brokenness, license, etc.  Throw a descriptive error if the check fails.
+  # Note: no dependencies are checked in this step, but this should be done before
+  #   applying the `derivation` primitive in order to "propagate to dependants".
+  addMetaCheckInner = config: meta: drv:
     let
       name = drv.name or "«name-missing»";
       position = meta.position or "«unknown-file»";
       v = checkMetaValidity { inherit meta config; inherit (drv) system; };
     in
-      if v.valid then drv
+      # As a compromise, do the check when evaluating the name attribute;
+      #   the intention is to also catch any attempt to show in nix-env -qa,
+      #   while allowing to query meta (surprisingly even --no-name doesn't break that).
+      drv // {
+        name = if v.valid then drv.name
           else throwEvalHelp (removeAttrs v ["valid"] // { inherit name position; });
+      };
+
+  # Make sure the dependencies are evaluted when accessing the name.
+  # The input is a derivation, i.e. *after* applying the `derivation` primitive.
+  addMetaCheckOuter = drv:
+    drv // { name = assert drv.outPath != null; drv.name; };
 
   # Throw a descriptive error message for a failed evaluation check.
   throwEvalHelp = { reason, errormsg, name, position }:

pkgs/stdenv/generic/default.nix

@@ -169,7 +169,7 @@ let
     in
 
       lib.addPassthru
-        (derivation (lib.addMetaCheck config meta derivationArg))
+        (lib.addMetaCheckOuter (derivation (lib.addMetaCheckInner config meta derivationArg)))
         ( {
             overrideAttrs = f: mkDerivation (attrs // (f attrs));
             inherit meta passthru;

pkgs/top-level/release-lib.nix

@@ -85,6 +85,9 @@ rec {
   packagePlatforms = mapAttrs (name: value:
     let res = builtins.tryEval (
       if isDerivation value then
+        # Hopefully a reliable way to test whether the derivation evaluates,
+        # including brokenness/license checks in any dependencies.
+        assert value.outPath != null;
         value.meta.hydraPlatforms or (value.meta.platforms or [ "x86_64-linux" ])
       else if value.recurseForDerivations or false || value.recurseForRelease or false then
         packagePlatforms value