The path templates feature implemented in #134860 highlights path
properties that have syntax errors in red and provides a list of those
errors in the path's tool tip. However, syntax errors are not the only
kind of error.
For example, if given the render output path `//render/{blend_nam}`,
with a typo in the variable `blend_name`, this error is not indicated
until actually trying to render. This is because the path is
*syntactically* correct, and the error is due to `blend_nam` not being
an available variable.
This PR resolves this: paths with path template support now indicate all
errors in the UI, not just syntax errors, with red highlights and a list
of errors in the tool tip.
The primary mechanisms for this are:
- A new function `BKE_build_template_variables_for_prop()`, which takes
an RNA pointer and produces an appropriate template variable map for the
given property, which can then be used to fully validate a path
property's value in the UI code.
- A new enum `PropertyPathTemplateType` has been added to `PropertyRNA`,
which determines what variables should be made available to a property
and how they should be build. This is used by
`BKE_build_template_variables_for_prop()`.
Additionally, the following changes have been made to help ensure that
`BKE_path_apply_template()` and `BKE_path_validate_template()` produce
identical errors:
- Both functions now call into a third static function `eval_template()`
that does the actual work, optionally modifying the input path or not.
- Previously only `BKE_path_apply_template()` had unit tests, but now
the unit tests have been reorganized to simultaneously test both
`BKE_path_apply_template()` and `BKE_path_validate_template()`.
Pull Request: https://projects.blender.org/blender/blender/pulls/138679
5ff12bdc98