doc: lib.customization: add Type and Example tags

Add the "Type:" blocks.
Move the examples below the descriptions whenever possibles
Add "Example:" tags before the examples moved below the descriptions.

lib/customisation.nix

@@ -13,16 +13,7 @@ rec {
      scenarios (e.g. in ~/.config/nixpkgs/config.nix).  For instance,
      if you want to "patch" the derivation returned by a package
      function in Nixpkgs to build another version than what the
-     function itself provides, you can do something like this:
-
-       mySed = overrideDerivation pkgs.gnused (oldAttrs: {
-         name = "sed-4.2.2-pre";
-         src = fetchurl {
-           url = ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2;
-           hash = "sha256-MxBJRcM2rYzQYwJ5XKxhXTQByvSg5jZc5cSHEZoB2IY=";
-         };
-         patches = [];
-       });
+     function itself provides.
 
      For another application, see build-support/vm, where this
      function is used to build arbitrary derivations inside a QEMU
@@ -35,6 +26,19 @@ rec {
 
      You should in general prefer `drv.overrideAttrs` over this function;
      see the nixpkgs manual for more information on overriding.
+
+     Example:
+       mySed = overrideDerivation pkgs.gnused (oldAttrs: {
+         name = "sed-4.2.2-pre";
+         src = fetchurl {
+           url = ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2;
+           hash = "sha256-MxBJRcM2rYzQYwJ5XKxhXTQByvSg5jZc5cSHEZoB2IY=";
+         };
+         patches = [];
+       });
+
+     Type:
+       overrideDerivation :: Derivation -> ( Derivation -> AttrSet ) -> Derivation
   */
   overrideDerivation = drv: f:
     let
@@ -55,6 +59,11 @@ rec {
      injects `override` attribute which can be used to override arguments of
      the function.
 
+     Please refer to "Nixpkgs Contributors Guide" section
+     "<pkg>.overrideDerivation" to learn about `overrideDerivation` and caveats
+     related to its use.
+
+     Example:
        nix-repl> x = {a, b}: { result = a + b; }
 
        nix-repl> y = lib.makeOverridable x { a = 1; b = 2; }
@@ -65,9 +74,8 @@ rec {
        nix-repl> y.override { a = 10; }
        { override = «lambda»; overrideDerivation = «lambda»; result = 12; }
 
-     Please refer to "Nixpkgs Contributors Guide" section
-     "<pkg>.overrideDerivation" to learn about `overrideDerivation` and caveats
-     related to its use.
+     Type:
+       makeOverridable :: (AttrSet -> a) -> AttrSet -> a
   */
   makeOverridable = f: lib.setFunctionArgs
     (origArgs: let
@@ -105,20 +113,29 @@ rec {
     `autoArgs`.  This function is intended to be partially
     parameterised, e.g.,
 
+      ```nix
       callPackage = callPackageWith pkgs;
       pkgs = {
         libfoo = callPackage ./foo.nix { };
         libbar = callPackage ./bar.nix { };
       };
+      ```
 
     If the `libbar` function expects an argument named `libfoo`, it is
     automatically passed as an argument.  Overrides or missing
     arguments can be supplied in `args`, e.g.
 
+      ```nix
       libbar = callPackage ./bar.nix {
         libfoo = null;
         enableX11 = true;
       };
+      ```
+
+    <!-- TODO: Apply "Example:" tag to the examples above -->
+
+    Type:
+      callPackageWith :: AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a
   */
   callPackageWith = autoArgs: fn: args:
     let
@@ -129,7 +146,7 @@ rec {
       # This includes automatic ones and ones passed explicitly
       allArgs = builtins.intersectAttrs fargs autoArgs // args;
 
-      # A list of argument names that the function requires, but
+      # a list of argument names that the function requires, but
       # wouldn't be passed to it
       missingArgs = lib.attrNames
         # Filter out arguments that have a default value
@@ -176,7 +193,11 @@ rec {
 
   /* Like callPackage, but for a function that returns an attribute
      set of derivations. The override function is added to the
-     individual attributes. */
+     individual attributes.
+
+     Type:
+       callPackagesWith :: AttrSet -> ((AttrSet -> AttrSet) | Path) -> AttrSet -> AttrSet
+  */
   callPackagesWith = autoArgs: fn: args:
     let
       f = if lib.isFunction fn then fn else import fn;
@@ -193,7 +214,11 @@ rec {
 
 
   /* Add attributes to each output of a derivation without changing
-     the derivation itself and check a given condition when evaluating. */
+     the derivation itself and check a given condition when evaluating.
+
+     Type:
+       extendDerivation :: Bool -> Any -> Derivation -> Derivation
+  */
   extendDerivation = condition: passthru: drv:
     let
       outputs = drv.outputs or [ "out" ];
@@ -227,7 +252,11 @@ rec {
   /* Strip a derivation of all non-essential attributes, returning
      only those needed by hydra-eval-jobs. Also strictly evaluate the
      result to ensure that there are no thunks kept alive to prevent
-     garbage collection. */
+     garbage collection.
+
+     Type:
+       hydraJob :: (Derivation | Null) -> (Derivation | Null)
+  */
   hydraJob = drv:
     let
       outputs = drv.outputs or ["out"];
@@ -265,7 +294,11 @@ rec {
      called with the overridden packages. The package sets may be
      hierarchical: the packages in the set are called with the scope
      provided by `newScope` and the set provides a `newScope` attribute
-     which can form the parent scope for later package sets. */
+     which can form the parent scope for later package sets.
+
+     Type:
+       makeScope :: (AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a) -> (AttrSet -> AttrSet) -> AttrSet
+  */
   makeScope = newScope: f:
     let self = f self // {
           newScope = scope: newScope (self // scope);
@@ -287,7 +320,25 @@ rec {
     { inherit otherSplices keep extra f; };
 
   /* Like makeScope, but aims to support cross compilation. It's still ugly, but
-     hopefully it helps a little bit. */
+     hopefully it helps a little bit.
+
+     Type:
+       makeScopeWithSplicing' ::
+         { splicePackages :: Splice -> AttrSet
+         , newScope :: AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a
+         }
+         -> { otherSplices :: Splice, keep :: AttrSet -> AttrSet, extra :: AttrSet -> AttrSet }
+         -> AttrSet
+
+       Splice ::
+         { pkgsBuildBuild :: AttrSet
+         , pkgsBuildHost :: AttrSet
+         , pkgsBuildTarget :: AttrSet
+         , pkgsHostHost :: AttrSet
+         , pkgsHostTarget :: AttrSet
+         , pkgsTargetTarget :: AttrSet
+         }
+  */
   makeScopeWithSplicing' =
     { splicePackages
     , newScope