view CONTRIBUTING @ 37272:7d3bc1d4e871

templater: pass (context, mapping) down to unwraphybrid()

See the subsequent patches for why.

I initially thought it would be wrong to pass a mapping to flatten() and
stringify() since these functions may be applied to a tree of generators,
where each node should be bound to the mapping when it was evaluated. But,
actually that isn't a problem. If an intermediate node has to override a
mapping dict, it can do on unwraphybrid() and yield "unwrapped" generator
of byte strings:

   "{f(g(v))}"  # literal template example.
       ^^^^     # g() want to override a mapping, so it returns a wrapped
                # object 'G{V}' with partial mapping 'lm' attached.
     ^^^^^^^    # f() stringifies 'G{V}', starting from a mapping 'm'.
                # when unwrapping 'G{}', it updates 'm' with 'lm', and
                # passes it to 'V'.

This structure is important for the formatter (and the hgweb) to build a
static template keyword, which can't access a mapping dict until evaluation
phase.

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