Auto merge of #22532 - pnkfelix:arith-overflow, r=pnkfelix,eddyb

Rebase and follow-through on work done by @cmr and @aatch.

Implements most of rust-lang/rfcs#560. Errors encountered from the checks during building were fixed.

The checks for division, remainder and bit-shifting have not been implemented yet.

See also PR #20795

cc @Aatch ; cc @nikomatsakis

1 files changed, 19 insertions, 20 deletions

diff --git a/src/libsyntax/ext/deriving/encodable.rs b/src/libsyntax/ext/deriving/encodable.rs
index 8038074cee1..17687534d75 100644
--- a/src/libsyntax/ext/deriving/encodable.rs
+++ b/src/libsyntax/ext/deriving/encodable.rs
@@ -181,7 +181,6 @@ fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
         Struct(ref fields) => {
             let emit_struct_field = cx.ident_of("emit_struct_field");
             let mut stmts = Vec::new();
-            let last = fields.len() - 1;
             for (i, &FieldInfo {
                     name,
                     ref self_,
@@ -204,6 +203,7 @@ fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
                                                  lambda));
 
                 // last call doesn't need a try!
+                let last = fields.len() - 1;
                 let call = if i != last {
                     cx.expr_try(span, call)
                 } else {
@@ -240,25 +240,24 @@ fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
             let encoder = cx.expr_ident(trait_span, blkarg);
             let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
             let mut stmts = Vec::new();
-            let last = fields.len() - 1;
-            for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
-                let enc = cx.expr_method_call(span, self_.clone(),
-                                              encode, vec!(blkencoder.clone()));
-                let lambda = cx.lambda_expr_1(span, enc, blkarg);
-                let call = cx.expr_method_call(span, blkencoder.clone(),
-                                               emit_variant_arg,
-                                               vec!(cx.expr_usize(span, i),
-                                                 lambda));
-                let call = if i != last {
-                    cx.expr_try(span, call)
-                } else {
-                    cx.expr(span, ExprRet(Some(call)))
-                };
-                stmts.push(cx.stmt_expr(call));
-            }
-
-            // enums with no fields need to return Ok()
-            if stmts.len() == 0 {
+            if fields.len() > 0 {
+                let last = fields.len() - 1;
+                for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
+                    let enc = cx.expr_method_call(span, self_.clone(),
+                                                  encode, vec!(blkencoder.clone()));
+                    let lambda = cx.lambda_expr_1(span, enc, blkarg);
+                    let call = cx.expr_method_call(span, blkencoder.clone(),
+                                                   emit_variant_arg,
+                                                   vec!(cx.expr_usize(span, i),
+                                                        lambda));
+                    let call = if i != last {
+                        cx.expr_try(span, call)
+                    } else {
+                        cx.expr(span, ExprRet(Some(call)))
+                    };
+                    stmts.push(cx.stmt_expr(call));
+                }
+            } else {
                 let ret_ok = cx.expr(trait_span,
                                      ExprRet(Some(cx.expr_ok(trait_span,
                                                              cx.expr_tuple(trait_span, vec![])))));