feat: add dynamic file structures in loop using yield-tag

copier/errors.py

@@ -112,6 +112,12 @@ def __init__(self, features: Sequence[str]):
         )
 
 
+class YieldTagInFileError(CopierError):
+    """A yield tag is used in the file content, but it is not allowed."""
+
+    pass
+
+
 # Warnings
 class CopierWarning(Warning):
     """Base class for all other Copier warnings."""

copier/main.py

@@ -42,6 +42,7 @@
     ExtensionNotFoundError,
     UnsafeTemplateError,
     UserMessageError,
+    YieldTagInFileError,
 )
 from .jinja_ext import YieldEnvironment, YieldExtension
 from .subproject import Subproject
@@ -615,6 +616,10 @@ def _render_template(self) -> None:
                     self._render_folder(dst_relpath)
                 else:
                     self._render_file(src_relpath, dst_relpath, extra_context=ctx or {})
+                    if self.jinja_env.yield_context:
+                        raise YieldTagInFileError(
+                            f"File {src_relpath} contains a yield tag, but it was not allowed."
+                        )
 
     def _render_file(
         self,

tests/test_dynamic_file_structures.py

@@ -3,6 +3,7 @@
 import pytest
 
 import copier
+from copier.errors import YieldTagInFileError
 from tests.helpers import build_file_tree
 
 
@@ -163,3 +164,25 @@ def test_folder_loop_dict_items(tmp_path_factory: pytest.TempPathFactory) -> Non
         unexpected_files = set(all_files) - set(expected_files)
 
         assert not unexpected_files, f"Unexpected files found: {unexpected_files}"
+
+
+def test_raise_yield_tag_in_file(tmp_path_factory: pytest.TempPathFactory) -> None:
+    src, dst = map(tmp_path_factory.mktemp, ("src", "dst"))
+    build_file_tree(
+        {
+            src / "copier.yml": "",
+            src
+            / "file.txt.jinja": "{% yield item from strings %}{{ item }}{% endyield %}",
+        }
+    )
+
+    with pytest.raises(YieldTagInFileError, match="file.txt.jinja"):
+        copier.run_copy(
+            str(src),
+            dst,
+            data={
+                "strings": ["a", "b", "c"],
+            },
+            defaults=True,
+            overwrite=True,
+        )