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Some places in the compiler, and many places in macros, use
`untypecheck` (aka `resetAttrs`) to strip types and local symbols
from a tree before retypechecking it under some different context.
The refactoring of the desugaring of vals and vars in Scala 2.12.0
broke an assumption in this facility.
When a ValDef must be split into multiple members (e.g. a field and
a getter, or a perhaps also a setter), the ValDef that was parsed
assumes the role of the `field`, and the trees for other members are
stached by `Namer` to the `synthetics` map of the compilation unit,
in order to spliced into the right statement list by typechecking.
See `enterGetterSetter` for more details.
However, the parsed ValDef is now used verbatim, carrying the meaning
(ie, the symbol) of the `private[this]` field. This tree now had
an inconsistency between the flags in `tree.mods.flags` and
`tree.symbol.flags`. `tree.name` also differed from `tree.symbol.name`
(the latter was renamed to be a local name, ie one with a trailing space.)
When `ResetAttrs` stripped off the symbol and we retypechecked, we'd
end up with two symbols in scope with the same name.
In the first from the `run` test:
```
================================================================================
{
class a extends scala.AnyRef {
def <init>(): a = {
a.super.<init>();
()
};
private[this] val x: Int = 42;
<stable> <accessor> def x: Int = a.this.x
};
new a()
}
{
class a extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
val x = 42; // oops, the name is "x" rather than "x " and we've missing `private[this]`!
<stable> <accessor> def x: Int = a.this.x
};
new a()
}
scala.tools.reflect.ToolBoxError: reflective typecheck has failed: x is already defined as value x
```
This commit uses the flags and name of the symbol in `typedValDef`.
I've also had to modify the internals of `CodePrinter` to use the
implicit, override, and deferred flags from the modifiers of an
accessor when recovering pre-typer tree for a ValDef.
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