Add buildDhall*Package support for generating documentation

The `buildDhall{Directory,GitHub}Package` utilities now take an
optional `document` argument for generating documentation using
`dhall-docs`.  The documentation is stored underneath the `./docs`
subdirectory of the build product.

pkgs/development/interpreters/dhall/build-dhall-directory-package.nix

@@ -14,12 +14,17 @@ lib.makePackageOverridable
     , src
     , # The file to import, relative to the root directory
       file ? "package.dhall"
+      # Set to `true` to generate documentation for the package
+    , document ? false
     }:
 
-    buildDhallPackage {
-      inherit name dependencies source;
+    buildDhallPackage
+      ( { inherit name dependencies source;
 
           code = "${src}/${file}";
+
         }
+      // lib.optionalAttrs document { documentationRoot = src; }
+      )
   )
 

pkgs/development/interpreters/dhall/build-dhall-github-package.nix

@@ -12,6 +12,8 @@ lib.makePackageOverridable
       directory ? ""
     , # The file to import, relative to the above directory
       file ? "package.dhall"
+      # Set to `true` to generate documentation for the package
+    , document ? false
 
       # Arguments passed through to `fetchFromGitHub`
     , owner
@@ -22,10 +24,6 @@ lib.makePackageOverridable
     , ...
     }@args:
 
-    buildDhallPackage {
-      inherit name dependencies source;
-
-      code =
     let
       src = fetchFromGitHub ({
         name = "${name}-source";
@@ -34,6 +32,7 @@ lib.makePackageOverridable
       } // removeAttrs args [
         "name"
         "dependencies"
+        "document"
         "source"
         "directory"
         "file"
@@ -45,6 +44,12 @@ lib.makePackageOverridable
       prefix = lib.optionalString (directory != "") "${directory}/";
 
     in
-          "${src}/${prefix}${file}";
+      buildDhallPackage
+        ( { inherit name dependencies source;
+
+            code = "${src}/${prefix}${file}";
           }
+        // lib.optionalAttrs document
+          { documentationRoot = "${src}/${prefix}"; }
+        )
   )

pkgs/development/interpreters/dhall/build-dhall-package.nix

@@ -1,4 +1,4 @@
-{ dhall, haskell, lib, lndir, runCommand, writeText }:
+{ dhall, dhall-docs, haskell, lib, lndir, runCommand, writeText }:
 
 { name
 
@@ -31,6 +31,12 @@
   # space within the Nix store, but if you set the following `source` option to
   # `true` then the package will also include `source.dhall`.
 , source ? false
+
+  # Directory to generate documentation for (i.e. as the `--input` option to the
+  # `dhall-docs` command.)
+  #
+  # If `null`, then no documentation is generated.
+, documentationRoot ? null
 }:
 
 let
@@ -42,8 +48,12 @@ let
 
   cache = ".cache";
 
+  data = ".local/share";
+
   cacheDhall = "${cache}/dhall";
 
+  dataDhall = "${data}/dhall";
+
   sourceFile = "source.dhall";
 
 in
@@ -71,4 +81,10 @@ in
     echo "missing $SHA_HASH" > $out/binary.dhall
 
     ${lib.optionalString (!source) "rm $out/${sourceFile}"}
+
+    ${lib.optionalString (documentationRoot != null) ''
+    mkdir -p $out/${dataDhall}
+
+    XDG_DATA_HOME=$out/${data} ${dhall-docs}/bin/dhall-docs --input '${documentationRoot}' --output-link $out/docs
+    ''}
   ''

pkgs/top-level/all-packages.nix

@@ -10310,13 +10310,15 @@ in
 
   dhall = haskell.lib.justStaticExecutables haskellPackages.dhall;
 
-  dhall-nix = haskell.lib.justStaticExecutables haskellPackages.dhall-nix;
-
   dhall-bash = haskell.lib.justStaticExecutables haskellPackages.dhall-bash;
 
+  dhall-docs = haskell.lib.justStaticExecutables haskellPackages.dhall-docs;
+
+  dhall-lsp-server = haskell.lib.justStaticExecutables haskellPackages.dhall-lsp-server;
+
   dhall-json = haskell.lib.justStaticExecutables haskellPackages.dhall-json;
 
-  dhall-lsp-server = haskell.lib.justStaticExecutables haskellPackages.dhall-lsp-server;
+  dhall-nix = haskell.lib.justStaticExecutables haskellPackages.dhall-nix;
 
   dhall-text = haskell.lib.justStaticExecutables haskellPackages.dhall-text;