This implementation required a compromise between parser
performance and AST structuring. On the one hand, Parse
must be fast in order to keep things in the IDE zippy, on
the other we must hit the disk to properly resolve 'canImport'
conditions and inject members of the active clause into the AST.
Additionally, a Parse-only pass may not provide platform-specific
information to the compiler invocation and so may mistakenly
activate or de-activate branches in the if-configuration decl.
The compromise is to perform condition evaluation only when
continuing on to semantic analysis. This keeps the parser quick
and avoids the unpacking that parse does for active conditions
while still retaining the ability to see through to an active
condition when we know we're moving on to semantic analysis anyways.
This changes `getBaseName()` on `DeclName` to return a `DeclBaseName`
instead of an `Identifier`. All places that will continue to be
expecting an `Identifier` are changed to call `getBaseIdentifier` which
will later assert that the `DeclName` is actually backed by an
identifier and not a special name.
For transitional purposes, a conversion operator from `DeclBaseName` to
`Identifier` has been added that will be removed again once migration
to DeclBaseName has been completed in other parts of the compiler.
Unify approach to printing declaration names
Printing a declaration's name using `<<` and `getBaseName()` is be
independent of the return type of `getBaseName()` which will change in
the future from `Identifier` to `DeclBaseName`
Resolves: https://bugs.swift.org/browse/SR-4426
* Make IfConfigDecl be able to hold ASTNodes
* Parse #if as IfConfigDecl
* Stop enclosing toplevel #if into TopLevelCodeDecl.
* Eliminate IfConfigStmt
Fixes:
https://bugs.swift.org/browse/SR-3455https://bugs.swift.org/browse/SR-3663https://bugs.swift.org/browse/SR-4032https://bugs.swift.org/browse/SR-4031
Now, compilation conditions are validated at first, then evaluated. Also,
in non-Swift3 mode, '&&' now has higher precedence than '||'.
'A || B && C || D' are evaluated as 'A || (B && C) || D'.
Swift3 source breaking changes:
* [SR-3663] This used to be accepted and evaluate to 'true' because of short
circuit without any validation.
#if true || true * 12 = try Anything is OK?
print("foo")
#endif
In this change, remaining expressions are properly validated and
diagnosed if it's invalid.
* [SR-4031] Compound name references are now diagnosed as errors.
e.g. `#if os(foo:bar:)(macOS)` or `#if FLAG(x:y:)`
Swift3 compatibility:
* [SR-3663] The precedence of '||' and '&&' are still the same and the
following code evaluates to 'true'.
#if false || true && false
print("foo")
#endif
