Fixes ICE when using reexported unit-like structs

Fixes that unit-like structs cannot be used if they are reexported and
used in another crate. The compiler fails with an ICE, because unit-like
structs are exported as DefFn and the expression `UnitStruct` is
interpreted as function pointer instead of a call to the constructor.

To resolve this ambiguity tuple-like struct constructors are now exported
as CtorFn. When `rustc::metadata::decoder` finds a CtorFn it sets a new
flag `is_ctor` in DefFn to true.

Relevant changes are in `rustc::metadata::{encoder, decoder}` and in
`rustc::middle::ty`.

Closes #12660 and #16973.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/librustc/middle/astencode.rs b/src/librustc/middle/astencode.rs
index f40d6d47281..2bd145706aa 100644
--- a/src/librustc/middle/astencode.rs
+++ b/src/librustc/middle/astencode.rs
@@ -440,7 +440,7 @@ fn decode_def(dcx: &DecodeContext, doc: rbml::Doc) -> def::Def {
 impl tr for def::Def {
     fn tr(&self, dcx: &DecodeContext) -> def::Def {
         match *self {
-          def::DefFn(did, p) => def::DefFn(did.tr(dcx), p),
+          def::DefFn(did, p, is_ctor) => def::DefFn(did.tr(dcx), p, is_ctor),
           def::DefStaticMethod(did, wrapped_did2, p) => {
             def::DefStaticMethod(did.tr(dcx),
                                    match wrapped_did2 {