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With the new focus on quasiquotes in macro implementations, we now have
to change the way how inference of macro def return types works.
Previously, if the return type of a macro def wasn’t specified, we looked into
the signature of its macro impl, took its return type (which could only
be c.Expr[T]) and then assigned T to be the return type of the macro def.
We also had a convenient special case which inferred Any in case when
the body of the macro impl wasn’t an expr. That avoided reporting spurious
errors if the macro impl had its body typed incorrectly (because in that
case we would report a def/impl signature mismatch anyway) and also provided
a convenience by letting macro impls end with `???`.
However now we also allow macro impls to return c.Tree, which means that
we are no longer able to do any meaningful type inference, because c.Tree
could correspond to tree of any type.
Unfortunately, when coupled with the type inference special case described
above, this means that the users who migrate from exprs to quasiquotes
are going to face an unpleasant surprise. If they haven’t provided
explicit return types for their macro defs, those types are going to be
silently inferred as `Any`!
This commit plugs this loophole by prohibiting type inference from
non-expr return types of macro impls (not counting Nothing). Moreover,
it also deprecates c.Expr[T] => T inference in order to avoid confusion
when switching between exprs and quasiquotes.
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This is the first commit in the series. This commit only:
1) Splits Context into BlackboxContext and WhiteboxContext
2) Splits Macro into BlackboxMacro and WhiteboxMacro
3) Introduces the isBundle property in the macro impl binding
Here we just teach the compiler that macros can now be blackbox and whitebox,
without actually imposing any restrictions on blackbox macros. These
restrictions will come in subsequent commits.
For description and documentation of the blackbox/whitebox separation
see the official macro guide at the scaladoc website:
http://docs.scala-lang.org/overviews/macros/blackbox-whitebox.html
Some infrastructure work to make evolving macros easier:
compile partest-extras with quick so they can use latest library/reflect/...
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One of the previous commits relaxed the top-level restriction for bundles,
turning it into a requirement of staticness (i.e. bundles nested in static
objects are also okay now).
This means that we can now define bundles in repl. Almost.
There's still a little problem remaining that arises from the fact that
when compiling a line of input, repl doesn't automatically import all
previously defined symbols, but rather uses an heuristic to scan the
input and guess what symbols need to be imported.
Unfortunately for bundles, this heuristic fails, because when scanning
a macro definition that looks like `def foo = macro Macros.foo`, it thinks
that it's only necessary to import a term symbol called Macros (a vanilla
way of defining macro impls), but not a type symbol called Macros (a new
way of writing macro impls in bundles).
This commit fixes the problem by making the repl look for both term and
type symbols corresponding to the identifiers used in macro definitions.
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