gnu: Add python-tomli-w.

* gnu/packages/python-build.scm (python-tomli-w): New variable.

gnu/packages/python-build.scm

@@ -26,6 +26,7 @@ (define-module (gnu packages python-build)
   #:use-module (gnu packages)
   #:use-module ((guix licenses) #:prefix license:)
   #:use-module (guix build-system python)
+  #:use-module (guix gexp)
   #:use-module (guix download)
   #:use-module (guix git-download)
   #:use-module (guix packages))
@@ -92,6 +93,38 @@ (define-public python-toml
 Language (TOML) configuration files.")
     (license license:expat)))
 
+(define-public python-tomli-w
+  (package
+    (name "python-tomli-w")
+    (version "1.0.0")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (pypi-uri "tomli_w" version))
+       (sha256
+        (base32 "1fg13bfq5qy1ym4x77815nhxh1xpfs0drhn9r9464cz00m1l6qzl"))))
+    (build-system python-build-system)
+    (arguments
+     (list
+      #:tests? #f                       ;to avoid extra dependencies
+      #:phases
+      #~(modify-phases %standard-phases
+          ;; XXX: PEP 517 manual build copied from python-isort.
+          (replace 'build
+            (lambda _
+              (invoke "python" "-m" "build" "--wheel" "--no-isolation" ".")))
+          (replace 'install
+            (lambda _
+              (let ((whl (car (find-files "dist" "\\.whl$"))))
+                (invoke "pip" "--no-cache-dir" "--no-input"
+                        "install" "--no-deps" "--prefix" #$output whl)))))))
+    (native-inputs (list python-pypa-build python-flit-core))
+    (home-page "https://github.com/hukkin/tomli-w")
+    (synopsis "Minimal TOML writer")
+    (description "Tomli-W is a Python library for writing TOML.  It is a
+write-only counterpart to Tomli, which is a read-only TOML parser.")
+    (license license:expat)))
+
 (define-public python-pytoml
   (package
     (name "python-pytoml")