From ed7ccf2e48188c7e6536d9841ca0f5962c31de5f Mon Sep 17 00:00:00 2001
From: Thomas Williams <32936518+thomaswilliamsastro@users.noreply.github.com>
Date: Thu, 15 Oct 2026 10:05:47 +0100
Subject: [PATCH] Skip linear mosaic targets in ImagingChunkedHandler

Mosaic targets have no MS of their own, so ImagingChunkedHandler crashed
on init. Check for a linmos target up front, log a warning, and make
run_imaging and task_complete_gather_into_cubes no-ops, matching the
behaviour of the standard ImagingHandler.

Closes #350

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 CHANGELOG.md                            |  1 +
 phangsPipeline/handlerImagingChunked.py | 18 ++++++
 tests/test_handlerImagingChunked.py     | 75 +++++++++++++++++++++++++
 3 files changed, 94 insertions(+)
 create mode 100644 tests/test_handlerImagingChunked.py

diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb18198..30a8588 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -69,6 +69,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Ensure fits import adds Stokes axis in feather routines (#407).
 - Fixed regression in get_ghz_range_for_line (#409).
 - Remove obsolete keywords so legacy singledish pipeline works again (#410).
+- ``ImagingChunkedHandler`` skips linear mosaic targets rather than crashing (#413).
 
 ### Dependencies
 - Bump actions/upload-artifact from 6 to 7 (#313).
diff --git a/phangsPipeline/handlerImagingChunked.py b/phangsPipeline/handlerImagingChunked.py
index 2ab62ee..4c1c2db 100644
--- a/phangsPipeline/handlerImagingChunked.py
+++ b/phangsPipeline/handlerImagingChunked.py
@@ -112,6 +112,16 @@ def __init__(
             self.config = config
             self.product = product
 
+            # Linear mosaic targets have no MS of their own, so there is nothing to image.
+            # Skip them gracefully, as the standard ImagingHandler does
+            self.skip_target = self._kh.is_target_linmos(self.target)
+            if self.skip_target:
+                logger.warning(f"Target {self.target} is a linear mosaic, so has no visibilities to image. "
+                               "Skipping.")
+                self.chunk_params = {}
+                self.nchunks = 0
+                return
+
             # Enforce that chunked imaging be used for cubes only.
             # Otherwise, there's no need for this approach:
             is_line_product = self.product in self._kh.get_line_products()
@@ -419,6 +429,10 @@ def run_imaging(
                 do_export_to_fits = True
                 do_cleanup = True
 
+            if self.skip_target:
+                logger.warning(f"Target {self.target} is a linear mosaic. Skipping imaging.")
+                return
+
             cwd = os.getcwd()
 
             # Create the imaging directory if it doesn't exist
@@ -1485,6 +1499,10 @@ def task_complete_gather_into_cubes(self, root_name='all',
             Intended to create a final set of cubes.
             '''
 
+            if self.skip_target:
+                logger.warning(f"Target {self.target} is a linear mosaic. Skipping gathering into cubes.")
+                return
+
             accepted_root_names = ['dirty', 'singlescale', 'multiscale', None]
 
             if root_name == 'all':
diff --git a/tests/test_handlerImagingChunked.py b/tests/test_handlerImagingChunked.py
new file mode 100644
index 0000000..1f72769
--- /dev/null
+++ b/tests/test_handlerImagingChunked.py
@@ -0,0 +1,75 @@
+import importlib.util
+import os
+
+import pytest
+
+# Load the key writer directly, since importing the phangsPipelineTests package
+# pulls in the full (slow, side-effectful) legacy test suite
+_spec = importlib.util.spec_from_file_location(
+    "minimal_key_writer",
+    os.path.join(os.path.dirname(__file__), "..", "phangsPipelineTests", "minimal_key_writer.py"),
+)
+_mkw = importlib.util.module_from_spec(_spec)
+_spec.loader.exec_module(_mkw)
+MinimalKeyWriter = _mkw.MinimalKeyWriter
+
+_TARGET = "testgal_1"
+_MOSAIC = "testgal"
+_CONFIG = "C1"
+_PRODUCT = "co21"
+
+
+@pytest.fixture
+def mosaic_key_handler(tmp_path):
+    """KeyHandler where _MOSAIC is a linear mosaic of _TARGET, with no MS of its own."""
+
+    from phangsPipeline import handlerKeys as kh
+
+    writer = MinimalKeyWriter(
+        key_dir=tmp_path / "keys",
+        data_dir=tmp_path / "data",
+        ms_root=tmp_path / "uvdata",
+    )
+    master_key = writer.write_all(
+        target=_TARGET,
+        config=_CONFIG,
+        product=_PRODUCT,
+        ms_filename="missing.ms",
+        restfreq_GHz=230.538,
+        ra="12h00m00.0s",
+        dec="-30d00m00.0s",
+    )
+
+    # Add the mosaic as a target, and define it as a linear mosaic
+    with open(os.path.join(writer.key_dir, "target_definitions.txt"), "a") as f:
+        f.write(f"{_MOSAIC}\t12h00m00.0s\t-30d00m00.0s\t0\t15\n")
+    with open(os.path.join(writer.key_dir, "linearmosaic_definitions.txt"), "a") as f:
+        f.write(f"{_MOSAIC}\t{_TARGET}\n")
+
+    cwd = os.getcwd()
+    yield kh.KeyHandler(master_key=master_key)
+    os.chdir(cwd)
+
+
+@pytest.mark.casa
+def test_chunked_handler_skips_linmos_target(mosaic_key_handler):
+    """ImagingChunkedHandler should skip linear mosaic targets, rather than crash."""
+
+    from phangsPipeline.handlerImagingChunked import ImagingChunkedHandler
+
+    assert mosaic_key_handler.is_target_linmos(_MOSAIC)
+
+    im_handler = ImagingChunkedHandler(
+        target=_MOSAIC,
+        config=_CONFIG,
+        product=_PRODUCT,
+        key_handler=mosaic_key_handler,
+        make_temp_dir=False,
+    )
+
+    assert im_handler.skip_target
+    assert im_handler.nchunks == 0
+
+    # Neither of these should do anything, or raise
+    im_handler.run_imaging(do_all=True)
+    im_handler.task_complete_gather_into_cubes(root_name="all")