rollup merge of #23945: pnkfelix/gate-u-negate

Feature-gate  unsigned unary negate.

Discussed in weekly meeting here: https://github.com/rust-lang/meeting-minutes/blob/master/weekly-meetings/2015-03-31.md#feature-gate--expr

and also in the internals thread here: http://internals.rust-lang.org/t/forbid-unsigned-integer/752

4 files changed, 10 insertions, 4 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index ce1539c62f8..40390765dde 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -388,7 +388,7 @@ pub const CRATE_NODE_ID: NodeId = 0;
 /// When parsing and doing expansions, we initially give all AST nodes this AST
 /// node value. Then later, in the renumber pass, we renumber them to have
 /// small, positive ids.
-pub const DUMMY_NODE_ID: NodeId = -1;
+pub const DUMMY_NODE_ID: NodeId = !0;
 
 /// The AST represents all type param bounds as types.
 /// typeck::collect::compute_bounds matches these against
diff --git a/src/libsyntax/codemap.rs b/src/libsyntax/codemap.rs
index 6a00fff1860..c2f2c51ed2c 100644
--- a/src/libsyntax/codemap.rs
+++ b/src/libsyntax/codemap.rs
@@ -278,9 +278,9 @@ pub struct ExpnInfo {
 #[derive(PartialEq, Eq, Clone, Debug, Hash, RustcEncodable, RustcDecodable, Copy)]
 pub struct ExpnId(u32);
 
-pub const NO_EXPANSION: ExpnId = ExpnId(-1);
+pub const NO_EXPANSION: ExpnId = ExpnId(!0);
 // For code appearing from the command line
-pub const COMMAND_LINE_EXPN: ExpnId = ExpnId(-2);
+pub const COMMAND_LINE_EXPN: ExpnId = ExpnId(!1);
 
 impl ExpnId {
     pub fn from_llvm_cookie(cookie: c_uint) -> ExpnId {
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 4c01cecc67c..2aa405bf6df 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -152,6 +152,9 @@ const KNOWN_FEATURES: &'static [(&'static str, &'static str, Status)] = &[
 
     // #23121. Array patterns have some hazards yet.
     ("slice_patterns", "1.0.0", Active),
+
+    // Allows use of unary negate on unsigned integers, e.g. -e for e: u8
+    ("negate_unsigned", "1.0.0", Active),
 ];
 // (changing above list without updating src/doc/reference.md makes @cmr sad)
 
@@ -325,6 +328,7 @@ pub struct Features {
     pub allow_custom_derive: bool,
     pub simd_ffi: bool,
     pub unmarked_api: bool,
+    pub negate_unsigned: bool,
     /// spans of #![feature] attrs for stable language features. for error reporting
     pub declared_stable_lang_features: Vec<Span>,
     /// #![feature] attrs for non-language (library) features
@@ -346,6 +350,7 @@ impl Features {
             allow_custom_derive: false,
             simd_ffi: false,
             unmarked_api: false,
+            negate_unsigned: false,
             declared_stable_lang_features: Vec::new(),
             declared_lib_features: Vec::new()
         }
@@ -724,6 +729,7 @@ fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler,
         allow_custom_derive: cx.has_feature("custom_derive"),
         simd_ffi: cx.has_feature("simd_ffi"),
         unmarked_api: cx.has_feature("unmarked_api"),
+        negate_unsigned: cx.has_feature("negate_unsigned"),
         declared_stable_lang_features: accepted_features,
         declared_lib_features: unknown_features
     }
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index c2f323f98af..3e0c938649d 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -3053,7 +3053,7 @@ mod test {
     #[test]
     fn test_signed_int_to_string() {
         let pos_int = ast::LitInt(42, ast::SignedIntLit(ast::TyI32, ast::Plus));
-        let neg_int = ast::LitInt((-42) as u64, ast::SignedIntLit(ast::TyI32, ast::Minus));
+        let neg_int = ast::LitInt((!42 + 1) as u64, ast::SignedIntLit(ast::TyI32, ast::Minus));
         assert_eq!(format!("-{}", lit_to_string(&codemap::dummy_spanned(pos_int))),
                    lit_to_string(&codemap::dummy_spanned(neg_int)));
     }