rustc: Switch tuple structs to have private fields

This is a continuation of the work done in #13184 to make struct fields private
by default. This commit finishes RFC 4 by making all tuple structs have private
fields by default. Note that enum variants are not affected.

A tuple struct having a private field means that it cannot be matched on in a
pattern match (both refutable and irrefutable), and it also cannot have a value
specified to be constructed. Similarly to private fields, switching the type of
a private field in a tuple struct should be able to be done in a backwards
compatible way.

The one snag that I ran into which wasn't mentioned in the RFC is that this
commit also forbids taking the value of a tuple struct constructor. For example,
this code now fails to compile:

    mod a {
        pub struct A(int);
    }

    let a: fn(int) -> a::A = a::A; //~ ERROR: first field is private

Although no fields are bound in this example, it exposes implementation details
through the type itself. For this reason, taking the value of a struct
constructor with private fields is forbidden (outside the containing module).

RFC: 0004-private-fields

1 files changed, 6 insertions, 6 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 3a9cdfb56e3..0f082c7e2f1 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -493,10 +493,10 @@ pub enum Expr_ {
     ExprVstore(@Expr, ExprVstore),
     // First expr is the place; second expr is the value.
     ExprBox(@Expr, @Expr),
-    ExprVec(Vec<@Expr> , Mutability),
-    ExprCall(@Expr, Vec<@Expr> ),
-    ExprMethodCall(Ident, Vec<P<Ty>> , Vec<@Expr> ),
-    ExprTup(Vec<@Expr> ),
+    ExprVec(Vec<@Expr>, Mutability),
+    ExprCall(@Expr, Vec<@Expr>),
+    ExprMethodCall(Ident, Vec<P<Ty>>, Vec<@Expr>),
+    ExprTup(Vec<@Expr>),
     ExprBinary(BinOp, @Expr, @Expr),
     ExprUnary(UnOp, @Expr),
     ExprLit(@Lit),
@@ -508,14 +508,14 @@ pub enum Expr_ {
     // Conditionless loop (can be exited with break, cont, or ret)
     // FIXME #6993: change to Option<Name>
     ExprLoop(P<Block>, Option<Ident>),
-    ExprMatch(@Expr, Vec<Arm> ),
+    ExprMatch(@Expr, Vec<Arm>),
     ExprFnBlock(P<FnDecl>, P<Block>),
     ExprProc(P<FnDecl>, P<Block>),
     ExprBlock(P<Block>),
 
     ExprAssign(@Expr, @Expr),
     ExprAssignOp(BinOp, @Expr, @Expr),
-    ExprField(@Expr, Ident, Vec<P<Ty>> ),
+    ExprField(@Expr, Ident, Vec<P<Ty>>),
     ExprIndex(@Expr, @Expr),
 
     /// Expression that looks like a "name". For example,