gnu: Add python-mslice.

* gnu/packages/patches/python-mslice-matplotlib-3.6-compatibility.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add reference to it.
* gnu/packages/physics.scm (python-mslice): New variable.

Change-Id: I55b884b53bef3f59d466e8980a643e4ef78fa544

2 files changed, 89 insertions, 0 deletions

diff --git a/gnu/packages/patches/python-mslice-matplotlib-3.6-compatibility.patch b/gnu/packages/patches/python-mslice-matplotlib-3.6-compatibility.patch
new file mode 100644
index 00000000000..8bbb81224da
--- /dev/null
+++ b/gnu/packages/patches/python-mslice-matplotlib-3.6-compatibility.patch
@@ -0,0 +1,46 @@
+From: Danny Milosavljevic <dannym@friendly-machines.com>
+Date: 2026-02-13
+Subject: Fix compatibility with matplotlib 3.6+
+
+Matplotlib 3.6 removed the `message` Qt signal from NavigationToolbar2QT.
+The old API was:
+
+    message = QtCore.Signal(str)
+
+    def set_message(self, s):
+        self.message.emit(s)
+        self.locLabel.setText(s)
+
+The new API just updates the label directly with no signal:
+
+    def set_message(self, s):
+        self.locLabel.setText(s)
+
+Matplotlib provides no replacement signal.  The only way to intercept
+toolbar messages is to override the set_message method.
+
+This patch replaces the signal connection with a method override that
+forwards messages to the status bar.
+
+--- a/src/mslice/plotting/plot_window/plot_window.py
++++ b/src/mslice/plotting/plot_window/plot_window.py
+@@ -274,7 +274,18 @@ class PlotWindow(QtWidgets.QMainWindow):
+
+     def create_status_bar(self):
+         self.statusbar = QtWidgets.QStatusBar(self)
+-        self.stock_toolbar.message.connect(self.statusbar.showMessage)
++        # Matplotlib 3.6 removed the `message` Qt signal from
++        # NavigationToolbar2QT.  The old code was:
++        #
++        #     self.stock_toolbar.message.connect(self.statusbar.showMessage)
++        #
++        # Since matplotlib provides no replacement signal, we override
++        # set_message to forward messages to the status bar.
++        original_set_message = self.stock_toolbar.set_message
++        def set_message_forwarding_to_statusbar(s):
++            original_set_message(s)
++            self.statusbar.showMessage(s)
++        self.stock_toolbar.set_message = set_message_forwarding_to_statusbar
+         self.setStatusBar(self.statusbar)
+
+     def flag_as_kept(self):
diff --git a/gnu/packages/physics.scm b/gnu/packages/physics.scm
index 06acf991d08..828e0f9a9f5 100644
--- a/gnu/packages/physics.scm
+++ b/gnu/packages/physics.scm
@@ -168,6 +168,49 @@ scattering simulations.")
     (description "GOFit: Global Optimization for Fitting problems.")
     (license license:bsd-3)))
 
+(define-public python-mslice
+  (package
+    (name "python-mslice")
+    (version "2.14")
+    (source
+     (origin
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/mantidproject/mslice.git")
+             (commit version)))
+       (file-name (git-file-name name version))
+       (sha256
+        (base32 "1bbg9hyl6jxyk79hshvqvcbwbx48x6va5nyhavj5kjg6ybd0n8fd"))
+       (patches
+        (search-patches "python-mslice-matplotlib-3.6-compatibility.patch"))))
+    (build-system pyproject-build-system)
+    (arguments
+     (list #:tests? #f                    ;require mantid
+           #:phases
+           #~(modify-phases %standard-phases
+               (add-after 'unpack 'fix-compatibility
+                 (lambda _
+                   ;; dedent_interpd was an alias for interpd; the alias was
+                   ;; removed in
+                   ;; <https://github.com/matplotlib/matplotlib/pull/28826>.
+                   (substitute* "src/mslice/plotting/pyplot.py"
+                     (("@_docstring\\.dedent_interpd")
+                      "@_docstring.interpd"))
+                   ;; self.execute("cls") fails; use widget's clear() method.
+                   ;; <https://github.com/mantidproject/mslice/issues/1152>
+                   (substitute* "src/mslice/widgets/ipythonconsole/ipython_widget.py"
+                     (("self\\.execute\\(\"cls\"\\)")
+                      "self.clear()"))))
+               (delete 'sanity-check))))  ;would require mantid
+    (propagated-inputs (list python-matplotlib python-pyqt python-qtpy
+                             python-qtawesome))
+    (native-inputs (list python-pytest python-setuptools))
+    (home-page "https://github.com/mantidproject/mslice")
+    (synopsis "Performs slices and cuts of multi-dimensional data produced by Mantid")
+    (description "This package provides a tool for performing slices and cuts
+of multi-dimensional data produced by Mantid.")
+    (license license:gpl3+)))
+
 (define-public python-pycifrw
   (package
     (name "python-pycifrw")