diff options
Diffstat (limited to 'src/libsyntax')
| -rw-r--r-- | src/libsyntax/ext/expand.rs | 36 |
1 files changed, 32 insertions, 4 deletions
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs index 762363f3abe..b8766200ccd 100644 --- a/src/libsyntax/ext/expand.rs +++ b/src/libsyntax/ext/expand.rs @@ -147,11 +147,17 @@ pub fn expand_expr(e: @ast::Expr, fld: &mut MacroExpander) -> @ast::Expr { // ['<ident>:] loop { // match i.next() { // None => break, - // Some(<src_pat>) => <src_loop_block> + // Some(mut value) => { + // let <src_pat> = value; + // <src_loop_block> + // } // } // } // } // } + // + // (The use of the `let` is to give better error messages + // when the pattern is refutable.) let local_ident = token::gensym_ident("__i"); // FIXME #13573 let next_ident = fld.cx.ident_of("next"); @@ -167,11 +173,33 @@ pub fn expand_expr(e: @ast::Expr, fld: &mut MacroExpander) -> @ast::Expr { fld.cx.arm(span, vec!(none_pat), break_expr) }; - // `Some(<src_pat>) => <src_loop_block>` + // let <src_pat> = value; + let value_ident = token::gensym_ident("__value"); + // this is careful to use src_pat.span so that error + // messages point exact at that. + let local = @ast::Local { + ty: fld.cx.ty_infer(src_pat.span), + pat: src_pat, + init: Some(fld.cx.expr_ident(src_pat.span, value_ident)), + id: ast::DUMMY_NODE_ID, + span: src_pat.span, + source: ast::LocalFor + }; + let local = codemap::respan(src_pat.span, ast::DeclLocal(local)); + let local = @codemap::respan(span, ast::StmtDecl(@local, ast::DUMMY_NODE_ID)); + + // { let ...; <src_loop_block> } + let block = fld.cx.block(span, vec![local], + Some(fld.cx.expr_block(src_loop_block))); + + // `Some(mut value) => { ... }` + // Note the _'s in the name will stop any unused mutability warnings. + let value_pat = fld.cx.pat_ident_binding_mode(span, value_ident, + ast::BindByValue(ast::MutMutable)); let some_arm = fld.cx.arm(span, - vec!(fld.cx.pat_enum(span, some_path, vec!(src_pat))), - fld.cx.expr_block(src_loop_block)); + vec!(fld.cx.pat_enum(span, some_path, vec!(value_pat))), + fld.cx.expr_block(block)); // `match i.next() { ... }` let match_expr = { |