fix(gui): pop up "File already exists" instead of silently bumping the run

The Run guard called set_scan_kind(), which runs update_filename() and
skips to the next free run number before the existence check, so the
check never fired and the scan started under a new number without a
word. Now the check runs first, then a warning box names the existing
master file and the run number it moved to, and the run is blocked.

- Simple tab "Run rotation" had no guard at all; same guard added
- "Taken" also matches <run>_*_master.h5: X-ray Centering writes
  <run>_raster2d_master.h5, which the exact name missed
- Camera context-menu "Evaluate grid" presses the panel button, so it
  gets the guard and stays inert while the button is disabled
- Dead next_free_run_from() removed

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/aare/gui/main_window.py

@@ -1007,7 +1007,9 @@ class MainWindow(QMainWindow):
 
         self.sample_camera.autofocus.connect(self.daq.autofocus)
 
-        self.sample_camera.evaluate_grid.connect(self.raster.run_grid_scan)
+        # Context-menu "Evaluate grid" presses the panel button so it gets the
+        # same file-exists guard, and stays inert while the button is disabled.
+        self.sample_camera.evaluate_grid.connect(self.data_collection.raster.start_button.click)
         self.data_collection.raster.evaluate_grid.connect(self.raster.run_grid_scan)
         self.data_collection.raster.evaluate_grid_auto.connect(self.raster.run_grid_scan_auto)
 

src/aare/gui/panels/file_path_panel.py

@@ -1,3 +1,4 @@
+import glob
 import os
 from datetime import datetime
 from pathlib import Path
@@ -119,8 +120,13 @@ class FilePathPanel(QWidget):
     def _exists_for_run(self, expanded_base_with_run: str) -> bool:
         # expanded_base_with_run is the base without scan-kind transforms yet
         effective = self._effective_dataset_base(expanded_base_with_run)
-        # Consider master file and directory as taken
-        return os.path.exists(f"{effective}_master.h5") or os.path.exists(effective)
+        # Taken = master file, directory, or any derived dataset of this run:
+        # X-ray centering writes "<run>_raster2d_master.h5", not "<run>_master.h5".
+        return (
+            os.path.exists(f"{effective}_master.h5")
+            or os.path.exists(effective)
+            or bool(glob.glob(f"{effective}_*_master.h5"))
+        )
 
     def update_filename(self):
         dir_name = self.directory_edit.text()
@@ -158,7 +164,7 @@ class FilePathPanel(QWidget):
 
         # Preview label shows the effective path (what will be written)
         effective = self._effective_dataset_base(self._filename)
-        exists = os.path.exists(f"{effective}_master.h5") or os.path.exists(effective)
+        exists = self._exists_for_run(self._filename)
         self.file_name_label.setText(effective + "_master.h5")
         # Empty stylesheet = reset to the THEME text color (a hardcoded
         # "default" black would be invisible on the dark theme).
@@ -231,42 +237,26 @@ class FilePathPanel(QWidget):
     def effective_path_for_base(self, base_with_run: str) -> str:
         return self._effective_dataset_base(base_with_run)
 
-    def next_free_run_from(self, start_rn: int) -> tuple[int, str]:
-        # Compute next free run number and updated base
-        dir_name = self.directory_edit.text().replace("{prefix}", self.file_prefix_edit.text())
-        base = dir_name if dir_name.endswith("/") or dir_name == "" else dir_name + "/"
-        base += "run" if self.file_prefix_edit.text() == "" else self.file_prefix_edit.text()
+    def file_path_error_box(self, scan_kind: str) -> bool:
+        """Click-time guard for the Run buttons: True when the run may start.
 
-        rn = start_rn
-        while rn <= self.run_number_edit.maximum():
-            candidate_base = self._expand_macros(base, rn)
-            if not self._exists_for_run(candidate_base):
-                return rn, candidate_base
-            rn += 1
-        return start_rn, self._expand_macros(base, start_rn)
-
-    def file_path_error_box(self, scan_kind: str):
-        self.set_scan_kind(scan_kind)
-        base = self.filename  # same base we emit
-        effective = self.effective_path_for_base(base)
-        if os.path.exists(f"{effective}_master.h5") or os.path.exists(effective):
-            reply = QMessageBox.question(
+        The scan kind is set directly, not via set_scan_kind(): that calls
+        update_filename(), which silently skips to the next free run number,
+        so the existence check below could never fire and the user was never
+        told the file was already there.
+        """
+        self._scan_kind = scan_kind
+        exists = self._exists_for_run(self.filename)
+        path = self.effective_path_for_base(self.filename) + "_master.h5"
+        # Refresh the label for the clicked kind; on a clash this also moves
+        # the run number to the next free one, as every edit already does.
+        self.update_filename()
+        if exists:
+            QMessageBox.warning(
                 self,
                 "File exists",
-                # f"This file already exists:\n{effective}_master.h5\nDo you wish to overwrite?",
-                f"This file already exists:\n{effective}_master.h5\n Updating run number",
-                QMessageBox.StandardButton.Yes | QMessageBox.StandardButton.No,
-                QMessageBox.StandardButton.No,
+                f"File already exists:\n{path}\n\n"
+                f"Run number moved to {self.run_number_edit.value()}.",
             )
-            if reply == QMessageBox.StandardButton.No:
-                # bump run and update
-                curr = self.run_number_edit.value()
-                new_rn, _ = self.next_free_run_from(curr + 1)
-                self.run_number_edit.setValue(new_rn)
-                self.update_filename()
-                return False
-            else:
-                return False
             return False
-
         return True

src/aare/gui/panels/smart_rotation_panel.py

@@ -515,6 +515,13 @@ class SimpleRotationSettingsPanel(QWidget):
 
     @Slot()
     def run_measurement(self):
+        # Same file-exists guard as the Rotation tab; this panel is not a
+        # ScanSettingsPanel, so it has no check_before_run() to inherit.
+        file_path_panel = getattr(self.parent(), "file_path_panel", None)
+        if file_path_panel is not None and not file_path_panel.file_path_error_box(
+            scan_kind="rotation"
+        ):
+            return
         # Send exactly what the panel last calculated and displayed, rather
         # than re-reading the widgets: dtz, exposure and transmission are a
         # single consistent solution and must not be mixed with a newer entry.

tests/unit/gui/test_data_collection_settings.py

@@ -485,3 +485,87 @@ def test_transmission_rows_are_per_mode(panel, qapp, diffraction):
     raster_label = _grid_widget(raster._layout, 2, 0)
     assert isinstance(raster_label, QLabel)
     assert raster_label.text() == "Transmission"
+
+
+# ---------------------------------------------------------------------------
+# File path panel: the Run buttons must not overwrite an existing dataset
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture
+def file_panel(qapp):
+    from aare.gui.panels.file_path_panel import FilePathPanel
+
+    p = FilePathPanel()
+    p.directory_edit.setText("d")
+    p.file_prefix_edit.setText("x")
+    p.run_number_edit.setValue(1)
+    return p
+
+
+def _taken(monkeypatch, *suffixes):
+    from aare.gui.panels import file_path_panel
+
+    monkeypatch.setattr(
+        file_path_panel.os.path, "exists", lambda path: any(path.endswith(s) for s in suffixes)
+    )
+
+
+def test_run_is_blocked_with_a_popup_when_the_file_exists(file_panel, monkeypatch):
+    from PySide6.QtWidgets import QMessageBox
+
+    _taken(monkeypatch, "data/d/x_001_master.h5")
+    boxes = []
+    monkeypatch.setattr(QMessageBox, "warning", lambda *a, **k: boxes.append(a))
+
+    assert file_panel.file_path_error_box(scan_kind="rotation") is False
+    assert len(boxes) == 1
+    assert "data/d/x_001_master.h5" in boxes[0][2]
+    # The panel moved on to the next free run, so the next click can go ahead.
+    assert file_panel.run_number_edit.value() == 2
+    assert file_panel.file_path_error_box(scan_kind="rotation") is True
+    assert len(boxes) == 1
+
+
+def test_run_proceeds_when_the_file_is_free(file_panel, monkeypatch):
+    from PySide6.QtWidgets import QMessageBox
+
+    _taken(monkeypatch)
+    monkeypatch.setattr(QMessageBox, "warning", lambda *a, **k: pytest.fail("no popup expected"))
+
+    assert file_panel.file_path_error_box(scan_kind="rotation") is True
+    assert file_panel.run_number_edit.value() == 1
+
+
+def test_a_derived_dataset_counts_as_taken(file_panel, monkeypatch):
+    # X-ray centering writes <run>_raster2d_master.h5, not <run>_master.h5.
+    from aare.gui.panels import file_path_panel
+
+    _taken(monkeypatch)
+    monkeypatch.setattr(
+        file_path_panel.glob,
+        "glob",
+        lambda pat: ["hit"] if pat.endswith("raster/d/x_001_*_master.h5") else [],
+    )
+    monkeypatch.setattr(file_path_panel.QMessageBox, "warning", lambda *a, **k: None)
+
+    assert file_panel.file_path_error_box(scan_kind="raster") is False
+    assert file_panel.run_number_edit.value() == 2
+
+
+def test_simple_tab_run_is_blocked_by_the_file_guard(qapp):
+    from PySide6.QtWidgets import QWidget
+
+    from aare.gui.panels.smart_rotation_panel import SimpleRotationSettingsPanel
+
+    holder = QWidget()
+    cast(Any, holder).file_path_panel = types.SimpleNamespace(
+        file_path_error_box=lambda scan_kind: False
+    )
+    panel = SimpleRotationSettingsPanel(parent=holder)
+    requests = []
+    panel.rotation_scan.connect(requests.append)
+
+    panel.run_measurement()
+
+    assert requests == []