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Use const_eval in loops

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This commit is contained in:
mcarton 2016-02-07 18:10:03 +01:00
parent 93461afffc
commit 34812e82d0
2 changed files with 49 additions and 18 deletions
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45
src/loops.rs
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@ -1,11 +1,12 @@
use rustc::lint::*;
use rustc_front::hir::*;
use reexport::*;
use rustc_front::intravisit::{Visitor, walk_expr, walk_block, walk_decl};
use rustc::middle::ty;
use rustc::middle::def::Def;
use consts::{constant_simple, Constant};
use rustc::front::map::Node::NodeBlock;
use rustc::lint::*;
use rustc::middle::const_eval::EvalHint::ExprTypeChecked;
use rustc::middle::const_eval::{ConstVal, eval_const_expr_partial};
use rustc::middle::def::Def;
use rustc::middle::ty;
use rustc_front::hir::*;
use rustc_front::intravisit::{Visitor, walk_expr, walk_block, walk_decl};
use std::borrow::Cow;
use std::collections::{HashSet, HashMap};
@ -421,22 +422,36 @@ fn check_for_loop_reverse_range(cx: &LateContext, arg: &Expr, expr: &Expr) {
// if this for loop is iterating over a two-sided range...
if let ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
// ...and both sides are compile-time constant integers...
if let Some(start_idx @ Constant::Int(..)) = constant_simple(start_expr) {
if let Some(stop_idx @ Constant::Int(..)) = constant_simple(stop_expr) {
if let Ok(start_idx) = eval_const_expr_partial(&cx.tcx, start_expr, ExprTypeChecked, None) {
if let Ok(stop_idx) = eval_const_expr_partial(&cx.tcx, stop_expr, ExprTypeChecked, None) {
// ...and the start index is greater than the stop index,
// this loop will never run. This is often confusing for developers
// who think that this will iterate from the larger value to the
// smaller value.
if start_idx > stop_idx {
span_help_and_lint(cx,
let (sup, eq) = match (start_idx, stop_idx) {
(ConstVal::Int(start_idx), ConstVal::Int(stop_idx)) => (start_idx > stop_idx, start_idx == stop_idx),
(ConstVal::Uint(start_idx), ConstVal::Uint(stop_idx)) => (start_idx > stop_idx, start_idx == stop_idx),
_ => (false, false),
};
if sup {
let start_snippet = snippet(cx, start_expr.span, "_");
let stop_snippet = snippet(cx, stop_expr.span, "_");
span_lint_and_then(cx,
REVERSE_RANGE_LOOP,
expr.span,
"this range is empty so this for loop will never run",
&format!("Consider using `({}..{}).rev()` if you are attempting to iterate \
over this range in reverse",
stop_idx,
start_idx));
} else if start_idx == stop_idx {
|db| {
db.span_suggestion(expr.span,
"consider using the following if \
you are attempting to iterate \
over this range in reverse",
format!("({}..{}).rev()` ",
stop_snippet,
start_snippet));
});
} else if eq {
// if they are equal, it's also problematic - this loop
// will never run.
span_lint(cx,