DOC: Use warnings instead of exceptions in gallery order

Exceptions cause a hard exit of sphinx, which is undesirable. Incorrect order specification should not break the build. It also make fixes harder since one one gets the first ordering issue and possibly would have to do multiple builds to see and fix multiple ordering issues.

Author: timhoffm

doc/sphinxext/gallery_order.py

@@ -7,6 +7,9 @@
 from pathlib import Path
 
 from sphinx_gallery.sorting import ExplicitOrder
+from sphinx.util import logging as sphinx_logging
+
+logger = sphinx_logging.getLogger(__name__)
 
 # Gallery sections shall be displayed in the following order.
 # Non-matching sections are inserted at the unsorted position
@@ -98,7 +101,7 @@ class MplFileExplicitOrder(ExplicitOrder):
     Use this if you want to ensure that a full order is intentionally maintained.
     """
     def __init__(self, src_dir):
-        ordered_list = self.read_gallery_order(Path(src_dir)) or []
+        ordered_list = self.read_gallery_order(Path(src_dir).resolve()) or []
         super().__init__(ordered_list)
 
     @staticmethod
@@ -135,13 +138,14 @@ def read_gallery_order(src_dir: Path):
         non_existing_examples = listed_examples - existing_examples
         missing_examples = existing_examples - listed_examples
 
+        rel_txt_path = gallery_order_txt.relative_to(gallery_order_txt.parents[3])
         if non_existing_examples:
-            raise ValueError(
-                f"The following examples listed in {gallery_order_txt} do not exist: "
+            logger.warning(
+                f"The following examples listed in {rel_txt_path} do not exist: "
                 f"{', '.join(non_existing_examples)}")
         if placeholder_index is None and missing_examples:
-            raise ValueError(
-                f"The following examples are not listed in {gallery_order_txt}. "
+            logger.warning(
+                f"The following examples are not listed in {rel_txt_path}. "
                 f"Either include them or add a '*' to indicate where not listed "
                 f"examples should be placed: "
                 f"{', '.join(missing_examples)}"