lib: Add getName to mirror getVersion

lib/default.nix

@@ -84,7 +84,8 @@ let
       hasInfix hasPrefix hasSuffix stringToCharacters stringAsChars escape
       escapeShellArg escapeShellArgs replaceChars lowerChars
       upperChars toLower toUpper addContextFrom splitString
-      removePrefix removeSuffix versionOlder versionAtLeast getVersion
+      removePrefix removeSuffix versionOlder versionAtLeast
+      getName getVersion
       nameFromURL enableFeature enableFeatureAs withFeature
       withFeatureAs fixedWidthString fixedWidthNumber isStorePath
       toInt readPathsFromFile fileContents;

lib/strings.nix

@@ -472,6 +472,23 @@ rec {
   */
   versionAtLeast = v1: v2: !versionOlder v1 v2;
 
+  /* This function takes an argument that's either a derivation or a
+     derivation's "name" attribute and extracts the name part from that
+     argument.
+
+     Example:
+       getName "youtube-dl-2016.01.01"
+       => "youtube-dl"
+       getName pkgs.youtube-dl
+       => "youtube-dl"
+  */
+  getName = x:
+   let
+     parse = drv: (builtins.parseDrvName drv).name;
+   in if isString x
+      then parse x
+      else x.pname or (parse x.name);
+
   /* This function takes an argument that's either a derivation or a
      derivation's "name" attribute and extracts the version part from that
      argument.