mkDerivation: Expose pname & version in meta

Nix only knows of `name` attribute and considers `pname` what parseDrvName
spits out. Unfortunately, that fails to account for many real-life packages
that have variants or dashes followed by number in their name.
Since many of packages in nixpkgs already have pname corresponding
to project name, we will export it here. We will fallback to the parseDrvName
algorithm when pname is not present.
We handle the version similarly.

This will be useful for Repology as well as any other scripted processing of
Nixpkgs JSON dump.

See: https://github.com/NixOS/nixos-homepage/issues/306

pkgs/stdenv/generic/check-meta.nix

@@ -188,7 +188,8 @@ let
     # Weirder stuff that doesn't appear in the documentation?
     knownVulnerabilities = listOf str;
     name = str;
-    version = str;
+    pname = str;
+    version = nullOr str;
     tag = str;
     updateWalker = bool;
     executables = listOf str;

pkgs/stdenv/generic/make-derivation.nix

@@ -286,6 +286,16 @@ in rec {
           # lets have a clean always accessible version here.
           name = attrs.name or "${attrs.pname}-${attrs.version}";
 
+          # Nix only knows of `name` attribute and considers `pname` what parseDrvName
+          # spits out. Unfortunately, that fails to account for many real-life packages
+          # that have variants or dashes followed by number in their name.
+          # Since many of packages in nixpkgs already have pname corresponding
+          # to project name, we will export it here. We will fallback to the parseDrvName
+          # algorithm when pname is not present.
+          # We handle the version similarly.
+          pname = attrs.pname or (builtins.parseDrvName attrs.name).name;
+          version = attrs.version or ((x: if x != "" then x else null) (builtins.parseDrvName attrs.name).version);
+
           # If the packager hasn't specified `outputsToInstall`, choose a default,
           # which is the name of `p.bin or p.out or p`;
           # if he has specified it, it will be overridden below in `// meta`.