Add Symlink(Output) class

omicron/ssg/output/__init__.py

@@ -1,13 +1,15 @@
-from omicron.ssg.output.output import Output
+from omicron.ssg.output.output import Output, OutputError
 from omicron.ssg.output.content import Content, ContentError
 from omicron.ssg.output.factory import create_content, is_content
 from omicron.ssg.output.file import File
 from omicron.ssg.output.index import Index, discover_index
 from omicron.ssg.output.memory import Memory
+from omicron.ssg.output.symlink import Symlink
 from omicron.ssg.output.tags import Tags, discover_tags
 
 __all__ = [
     "Output",
+    "OutputError",
     "Content",
     "ContentError",
     "create_content",
@@ -16,6 +18,7 @@ __all__ = [
     "Index",
     "discover_index",
     "Memory",
+    "Symlink",
     "Tags",
     "discover_tags",
 ]

omicron/ssg/output/content.py

@@ -1,6 +1,6 @@
 import re
 from typing import TYPE_CHECKING
-from omicron.ssg.output.output import Output
+from omicron.ssg.output.output import Output, OutputError
 from pathlib import Path
 from datetime import date
 
@@ -10,7 +10,7 @@ else:
     Site = "omicron.ssg.site.Site"
 
 
-class ContentError(RuntimeError):
+class ContentError(OutputError):
     pass
 
 

omicron/ssg/output/output.py

@@ -9,6 +9,10 @@ else:
     Site = "omicron.ssg.site.Site"  # for runtime checking with beartype
 
 
+class OutputError(RuntimeError):
+    pass
+
+
 class Output(ABC):
     def __init__(self, site: Site, destination: Path):
         self._site_ref = weakref.ref(site)

omicron/ssg/output/symlink.py

@@ -0,0 +1,38 @@
+import logging
+import os
+from typing import TYPE_CHECKING
+from omicron.ssg.output.output import Output, OutputError
+from pathlib import Path
+
+log = logging.getLogger(__name__)
+
+if TYPE_CHECKING:
+    from omicron.ssg.site import Site  # for static checking with mypy
+else:
+    Site = "omicron.ssg.site.Site"  # for runtime checking with beartype
+
+
+class Symlink(Output):
+    def __init__(self, site: Site, link: Path, target: Path):
+        if target.is_absolute():
+            raise ValueError("Symlinks must be relative")
+        if (
+            not (site.output_path / target)
+            .resolve()
+            .is_relative_to(site.output_path.resolve())
+        ):
+            raise ValueError("Symlink target escapes the output directory")
+        super().__init__(site, link)
+        self.target = target
+
+    def write(self) -> None:
+        site = self.site
+        if self.target not in site.by_path:
+            raise OutputError(f"Symlink target '{self.target}' is not a known output")
+        link = site.output_path / self.destination
+        link.parent.mkdir(parents=True, exist_ok=True)
+        if link.exists() or link.is_symlink():
+            link.unlink()
+        rel_target = os.path.relpath(site.output_path / self.target, link.parent)
+        link.symlink_to(rel_target)
+        log.debug("Symlinked %s -> %s", link, rel_target)