Allow a single file to be expanded into a directory

This allows a file whose name is templated to be expanded into a directory
under its expanded name, so we can find out what that name is, even when we
are expanding just that one file.

Author: rrthomas

README.md

@@ -99,6 +99,9 @@ Nancy then processes each file:
   or directory in the output, the name in the input tree is expanded, and
   any `.nancy` suffix is removed. There is one exception: the root directory
   (or file) is called `OUTPUT` (that is, the `OUTPUT` argument to Nancy).
+  However, if `OUTPUT` already exists and is a directory, and the root is a
+  file, then the output is written with its expanded file name to the
+  directory `OUTPUT`.
 
 Input files, which are not copied to the output in any form, can be used by
 commands in other files. They can also be used for documentation or other

README.nancy.md

@@ -75,6 +75,9 @@ Nancy then processes each file:
   or directory in the output, the name in the input tree is expanded, and
   any `.nancy` suffix is removed. There is one exception: the root directory
   (or file) is called `OUTPUT` (that is, the `OUTPUT` argument to Nancy).
+  However, if `OUTPUT` already exists and is a directory, and the root is a
+  file, then the output is written with its expanded file name to the
+  directory `OUTPUT`.
 
 Input files, which are not copied to the output in any form, can be used by
 commands in other files. They can also be used for documentation or other

nancy/__init__.py

@@ -348,19 +348,29 @@ def __init__(
 
     async def set_output_path(self):
         """Recompute `_output_path` by expanding `path`."""
-        output_path = self.path.relative_to(self.tree.build)
-        if output_path.name != "":
-            if re.search(COPY_REGEX, output_path.name):
-                output_path = output_path.with_name(
-                    output_path.name.replace(".copy", "", 1)
-                )
+        # Compute expanded filename
+        if self.path.name != "":
+            if re.search(COPY_REGEX, self.path.name):
+                final_path = self.path.with_name(self.path.name.replace(".copy", "", 1))
             else:
-                output_path = output_path.with_name(
-                    re.sub(TEMPLATE_REGEX, "", output_path.name)
+                final_path = self.path.with_name(
+                    re.sub(TEMPLATE_REGEX, "", self.path.name)
                 )
             # Discard computed inputs when expanding filenames.
-            output, _ = await self.expand(bytes(output_path))
-            output_path = Path(os.fsdecode(output))
+            expanded_final_path, _ = await self.expand(bytes(final_path))
+            expanded_final_path = Path(os.fsdecode(expanded_final_path))
+        else:
+            expanded_final_path = Path("")
+
+        output_path = self.path.relative_to(self.tree.build)
+        if output_path.name != "":
+            output_path = output_path.with_name(expanded_final_path.name)
+        elif (
+            self.tree.output.exists()
+            and self.tree.output.is_dir()
+            and self.input_file().is_file()
+        ):
+            output_path = Path(expanded_final_path.name)
         self._output_path = output_path
 
     def input_file(self):

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "nancy"
-version = "13.0.2"
+version = "13.1.0"
 description = "Simple templating system"
 license = "GPL-3.0-or-later"
 authors = [

tests/test_nancy.py

@@ -401,6 +401,17 @@ async def test_expanding_macros_in_file_names() -> None:
         )
 
 
+async def test_expanding_macro_in_single_file_argument_with_directory_output() -> None:
+    with TemporaryDirectory() as tmp_dir:
+        with chdir(tests_dir):
+            await passing_test(
+                "expanding-macros-in-file-names-src",
+                "expanding-macros-in-file-names-expected",
+                "$include(name.in.txt).nancy.txt",
+                tmp_dir,
+            )
+
+
 async def test_run_with_input() -> None:
     with chdir(tests_dir):
         await passing_test(