This involves a little hack to insert a lambda parameter 'x' to be used at
keyword position. If the template language were dynamically typed (and were
interpreted), .map() implementation would be simpler. I considered that, but
interpreter version has its own warts (late error reporting, uneasy to cache
static object, etc.), and I don't think the current template engine is
complex enough to rewrite from scratch.
.map() returns template, which can't be join()-ed. This will be fixed later.
I'm thinking of rewriting the evaluation part as a simple interpreter. It
will increase the runtime cost (about a few microseconds per entry I suppose),
but will greatly reduce the complexity of generic property function chaining.
The extracted template_builder module is the part I'm going to reimplement.
A list type isn't so useful without a map operation, but List<CommitId>
is at least printable. Maybe we can experiment with it to craft a map
operation.
If a map operation is introduced, this keyword might be replaced with
"parents.map(|commit| commit.commit_id)", where parents is of List<Commit>
type, and the .map() method will probably return List<Template>.
This basically undoes d6c6cdb45c "templater: store type-erased version of
commit/change id." Since they are looked up differently, they should preserve
the original types.
FWIW, I'm thinking of making the repo parameter generic over Arc<ReadonlyRepo>
and &MutableRepo. It will allow us cache a parsed commit_summary template.
