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Auto merge of #33337 - birkenfeld:issue-27842, r=jseyfried

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typeck: show a note about tuple indexing for erroneous tup[i]

Fixes: #27842
This commit is contained in:
bors 2016-05-10 03:06:05 -07:00
commit 3585321d1e
2 changed files with 48 additions and 1 deletions
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25
src/librustc_typeck/check/mod.rs
View File

@ -3691,7 +3691,7 @@ fn check_expr_with_expectation_and_lvalue_pref<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
}
None => {
check_expr_has_type(fcx, &idx, fcx.tcx().types.err);
fcx.type_error_message(
let mut err = fcx.type_error_struct(
expr.span,
|actual| {
format!("cannot index a value of type `{}`",
@ -3699,6 +3699,29 @@ fn check_expr_with_expectation_and_lvalue_pref<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
},
base_t,
None);
// Try to give some advice about indexing tuples.
if let ty::TyTuple(_) = base_t.sty {
let mut needs_note = true;
// If the index is an integer, we can show the actual
// fixed expression:
if let hir::ExprLit(ref lit) = idx.node {
if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
let snip = fcx.tcx().sess.codemap().span_to_snippet(base.span);
if let Ok(snip) = snip {
err.span_suggestion(expr.span,
"to access tuple elements, use tuple \
indexing syntax as shown",
format!("{}.{}", snip, i));
needs_note = false;
}
}
}
if needs_note {
err.help("to access tuple elements, use tuple indexing \
syntax (e.g. `tuple.0`)");
}
}
err.emit();
fcx.write_ty(id, fcx.tcx().types.err);
}
}

24
src/test/compile-fail/issue-27842.rs Normal file
View File

@ -0,0 +1,24 @@
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
fn main() {
let tup = (0, 1, 2);
// the case where we show a suggestion
let _ = tup[0];
//~^ ERROR cannot index a value of type
//~| HELP to access tuple elements, use tuple indexing syntax as shown
//~| SUGGESTION let _ = tup.0
// the case where we show just a general hint
let i = 0_usize;
let _ = tup[i];
//~^ ERROR cannot index a value of type
//~| HELP to access tuple elements, use tuple indexing syntax (e.g. `tuple.0`)
}