thx rebuilds venvs with unrelated pyproject.toml changes

[lordmauve]

With many tools providing configuration in pyproject.toml, it slows down the development cycle considerably if changes to config cause venvs to be rebuilt.

For example, changing a tool.mypy setting in order to re-run thx mypy causes venvs to be rebuilt unnecessarily. this is also true of thx jobs themselves.

diff --git a/pyproject.toml b/pyproject.toml
index 84cf078..88cda16 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -137,7 +137,7 @@ addopts = [
 [tool.mypy]
 files = ["src", "tests"]
 mypy_path = ["stubs"]
-disallow_untyped_defs = false
+disallow_untyped_defs = true
 warn_redundant_casts = true
 warn_unreachable = true
 warn_unused_configs = true

To avoid this we should capture the sections of pyproject.toml that affect installation, e.g.

• build-system
• project
• tool.thx.requirements
• tool.thx.extras

There may be some settings that do affect package builds, like tool.flit.module.name, but these are changed rarely and there's always --clean.

Alternatively, we could tool keys corresponding to well-known build tools and add these to the list of keys we consider for venv invalidation.