use rustc::lint::*;
use rustc_front::hir::*;
use reexport::*;
use rustc_front::visit::{Visitor, walk_expr, walk_block, walk_decl};
use rustc::middle::ty;
use rustc::middle::def::DefLocal;
use consts::{constant_simple, Constant};
use rustc::front::map::Node::{NodeBlock};
use std::collections::{HashSet,HashMap};
use syntax::ast::Lit_::*;
use utils::{snippet, span_lint, get_parent_expr, match_trait_method, match_type,
in_external_macro, expr_block, span_help_and_lint, is_integer_literal};
use utils::{VEC_PATH, LL_PATH};
declare_lint!{ pub NEEDLESS_RANGE_LOOP, Warn,
"for-looping over a range of indices where an iterator over items would do" }
declare_lint!{ pub EXPLICIT_ITER_LOOP, Warn,
"for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do" }
declare_lint!{ pub ITER_NEXT_LOOP, Warn,
"for-looping over `_.next()` which is probably not intended" }
declare_lint!{ pub WHILE_LET_LOOP, Warn,
"`loop { if let { ... } else break }` can be written as a `while let` loop" }
declare_lint!{ pub UNUSED_COLLECT, Warn,
"`collect()`ing an iterator without using the result; this is usually better \
written as a for loop" }
declare_lint!{ pub REVERSE_RANGE_LOOP, Warn,
"Iterating over an empty range, such as `10..0` or `5..5`" }
declare_lint!{ pub EXPLICIT_COUNTER_LOOP, Warn,
"for-looping with an explicit counter when `_.enumerate()` would do" }
#[derive(Copy, Clone)]
pub struct LoopsPass;
impl LintPass for LoopsPass {
fn get_lints(&self) -> LintArray {
lint_array!(NEEDLESS_RANGE_LOOP, EXPLICIT_ITER_LOOP, ITER_NEXT_LOOP,
WHILE_LET_LOOP, UNUSED_COLLECT, REVERSE_RANGE_LOOP, EXPLICIT_COUNTER_LOOP)
}
}
impl LateLintPass for LoopsPass {
fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
if let Some((pat, arg, body)) = recover_for_loop(expr) {
if let ExprRange(Some(ref l), _) = arg.node {
if let ExprLit(ref lit) = l.node {
if let LitInt(0, _) = lit.node {
if let PatIdent(_, ref ident, _) = pat.node {
let mut visitor = VarVisitor { cx: cx, var: ident.node.name,
indexed: HashSet::new(), nonindex: false };
walk_expr(&mut visitor, body);
if visitor.indexed.len() == 1 {
let indexed = visitor.indexed.into_iter().next().expect(
"Len was nonzero, but no contents found");
if visitor.nonindex {
span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
"the loop variable `{}` is used to index `{}`. Consider using \
`for ({}, item) in {}.iter().enumerate()` or similar iterators",
ident.node.name, indexed, ident.node.name, indexed));
} else {
span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
"the loop variable `{}` is only used to index `{}`. \
Consider using `for item in &{}` or similar iterators",
ident.node.name, indexed, indexed));
}
}
}
}
}
}
if let ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
if let Some(Constant::ConstantInt(start_idx, _)) = constant_simple(start_expr) {
if let Some(Constant::ConstantInt(stop_idx, _)) = constant_simple(stop_expr) {
if start_idx > stop_idx {
span_help_and_lint(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 {
span_lint(cx, REVERSE_RANGE_LOOP, expr.span,
"this range is empty so this for loop will never run");
}
}
}
}
if let ExprMethodCall(ref method, _, ref args) = arg.node {
if args.len() == 1 {
let method_name = method.node.name;
if method_name == "iter" || method_name == "iter_mut" {
if is_ref_iterable_type(cx, &args[0]) {
let object = snippet(cx, args[0].span, "_");
span_lint(cx, EXPLICIT_ITER_LOOP, expr.span, &format!(
"it is more idiomatic to loop over `&{}{}` instead of `{}.{}()`",
if method_name == "iter_mut" { "mut " } else { "" },
object, object, method_name));
}
}
else if method_name == "next" &&
match_trait_method(cx, arg, &["core", "iter", "Iterator"]) {
span_lint(cx, ITER_NEXT_LOOP, expr.span,
"you are iterating over `Iterator::next()` which is an Option; \
this will compile but is probably not what you want");
}
}
}
let mut visitor = IncrementVisitor { cx: cx, states: HashMap::new(), depth: 0, done: false };
walk_expr(&mut visitor, body);
let map = &cx.tcx.map;
let parent_scope = map.get_enclosing_scope(expr.id).and_then(|id| map.get_enclosing_scope(id) );
if let Some(parent_id) = parent_scope {
if let NodeBlock(block) = map.get(parent_id) {
for (id, _) in visitor.states.iter().filter( |&(_,v)| *v == VarState::IncrOnce) {
let mut visitor2 = InitializeVisitor { cx: cx, end_expr: expr, var_id: id.clone(),
state: VarState::IncrOnce, name: None,
depth: 0, done: false };
walk_block(&mut visitor2, block);
if visitor2.state == VarState::Warn {
if let Some(name) = visitor2.name {
span_lint(cx, EXPLICIT_COUNTER_LOOP, expr.span,
&format!("the variable `{0}` is used as a loop counter. Consider \
using `for ({0}, item) in {1}.enumerate()` \
or similar iterators",
name, snippet(cx, arg.span, "_")));
}
}
}
}
}
}
if let ExprLoop(ref block, _) = expr.node {
if let Some(inner) = extract_single_expr(block) {
if let ExprMatch(ref matchexpr, ref arms, ref source) = inner.node {
match *source {
MatchSource::Normal | MatchSource::IfLetDesugar{..} => if
arms.len() == 2 &&
arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
arms[1].pats.len() == 1 && arms[1].guard.is_none() &&
is_break_expr(&arms[1].body)
{
if in_external_macro(cx, expr.span) { return; }
span_help_and_lint(cx, WHILE_LET_LOOP, expr.span,
"this loop could be written as a `while let` loop",
&format!("try\nwhile let {} = {} {}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, matchexpr.span, ".."),
expr_block(cx, &arms[0].body, "..")));
},
_ => ()
}
}
}
}
}
fn check_stmt(&mut self, cx: &LateContext, stmt: &Stmt) {
if let StmtSemi(ref expr, _) = stmt.node {
if let ExprMethodCall(ref method, _, ref args) = expr.node {
if args.len() == 1 && method.node.name == "collect" &&
match_trait_method(cx, expr, &["core", "iter", "Iterator"]) {
span_lint(cx, UNUSED_COLLECT, expr.span, &format!(
"you are collect()ing an iterator and throwing away the result. \
Consider using an explicit for loop to exhaust the iterator"));
}
}
}
}
}
fn recover_for_loop(expr: &Expr) -> Option<(&Pat, &Expr, &Expr)> {
if_let_chain! {
[
let ExprMatch(ref iterexpr, ref arms, _) = expr.node,
let ExprCall(_, ref iterargs) = iterexpr.node,
iterargs.len() == 1 && arms.len() == 1 && arms[0].guard.is_none(),
let ExprLoop(ref block, _) = arms[0].body.node,
block.stmts.is_empty(),
let Some(ref loopexpr) = block.expr,
let ExprMatch(_, ref innerarms, MatchSource::ForLoopDesugar) = loopexpr.node,
innerarms.len() == 2 && innerarms[0].pats.len() == 1,
let PatEnum(_, Some(ref somepats)) = innerarms[0].pats[0].node,
somepats.len() == 1
], {
return Some((&somepats[0],
&iterargs[0],
&innerarms[0].body));
}
}
None
}
struct VarVisitor<'v, 't: 'v> {
cx: &'v LateContext<'v, 't>, var: Name, indexed: HashSet<Name>, nonindex: bool, }
impl<'v, 't> Visitor<'v> for VarVisitor<'v, 't> {
fn visit_expr(&mut self, expr: &'v Expr) {
if let ExprPath(None, ref path) = expr.node {
if path.segments.len() == 1 && path.segments[0].identifier.name == self.var {
if_let_chain! {
[
let Some(parexpr) = get_parent_expr(self.cx, expr),
let ExprIndex(ref seqexpr, _) = parexpr.node,
let ExprPath(None, ref seqvar) = seqexpr.node,
seqvar.segments.len() == 1
], {
self.indexed.insert(seqvar.segments[0].identifier.name);
return; }
}
self.nonindex = true;
return;
}
}
walk_expr(self, expr);
}
}
fn is_ref_iterable_type(cx: &LateContext, e: &Expr) -> bool {
let ty = cx.tcx.expr_ty(e);
is_iterable_array(ty) ||
match_type(cx, ty, &VEC_PATH) ||
match_type(cx, ty, &LL_PATH) ||
match_type(cx, ty, &["std", "collections", "hash", "map", "HashMap"]) ||
match_type(cx, ty, &["std", "collections", "hash", "set", "HashSet"]) ||
match_type(cx, ty, &["collections", "vec_deque", "VecDeque"]) ||
match_type(cx, ty, &["collections", "binary_heap", "BinaryHeap"]) ||
match_type(cx, ty, &["collections", "btree", "map", "BTreeMap"]) ||
match_type(cx, ty, &["collections", "btree", "set", "BTreeSet"])
}
fn is_iterable_array(ty: ty::Ty) -> bool {
match ty.sty {
ty::TyArray(_, 0...32) => true,
_ => false
}
}
fn extract_single_expr(block: &Block) -> Option<&Expr> {
match (&block.stmts.len(), &block.expr) {
(&1, &None) => match block.stmts[0].node {
StmtExpr(ref expr, _) |
StmtSemi(ref expr, _) => Some(expr),
_ => None,
},
(&0, &Some(ref expr)) => Some(expr),
_ => None
}
}
fn is_break_expr(expr: &Expr) -> bool {
match expr.node {
ExprBreak(None) => true,
ExprBlock(ref b) => match extract_single_expr(b) {
Some(ref subexpr) => is_break_expr(subexpr),
None => false,
},
_ => false,
}
}
#[derive(PartialEq)]
enum VarState {
Initial, IncrOnce, Declared, Warn,
DontWarn
}
struct IncrementVisitor<'v, 't: 'v> {
cx: &'v LateContext<'v, 't>, states: HashMap<NodeId, VarState>, depth: u32, done: bool
}
impl<'v, 't> Visitor<'v> for IncrementVisitor<'v, 't> {
fn visit_expr(&mut self, expr: &'v Expr) {
if self.done {
return;
}
if let Some(def_id) = var_def_id(self.cx, expr) {
if let Some(parent) = get_parent_expr(self.cx, expr) {
let state = self.states.entry(def_id).or_insert(VarState::Initial);
match parent.node {
ExprAssignOp(op, ref lhs, ref rhs) =>
if lhs.id == expr.id {
if op.node == BiAdd && is_integer_literal(rhs, 1) {
*state = match *state {
VarState::Initial if self.depth == 0 => VarState::IncrOnce,
_ => VarState::DontWarn
};
}
else {
*state = VarState::DontWarn;
}
},
ExprAssign(ref lhs, _) if lhs.id == expr.id => *state = VarState::DontWarn,
ExprAddrOf(mutability,_) if mutability == MutMutable => *state = VarState::DontWarn,
_ => ()
}
}
}
else if is_loop(expr) {
self.states.clear();
self.done = true;
return;
}
else if is_conditional(expr) {
self.depth += 1;
walk_expr(self, expr);
self.depth -= 1;
return;
}
walk_expr(self, expr);
}
}
struct InitializeVisitor<'v, 't: 'v> {
cx: &'v LateContext<'v, 't>, end_expr: &'v Expr, var_id: NodeId,
state: VarState,
name: Option<Name>,
depth: u32, done: bool
}
impl<'v, 't> Visitor<'v> for InitializeVisitor<'v, 't> {
fn visit_decl(&mut self, decl: &'v Decl) {
if let DeclLocal(ref local) = decl.node {
if local.pat.id == self.var_id {
if let PatIdent(_, ref ident, _) = local.pat.node {
self.name = Some(ident.node.name);
self.state = if let Some(ref init) = local.init {
if is_integer_literal(init, 0) {
VarState::Warn
} else {
VarState::Declared
}
}
else {
VarState::Declared
}
}
}
}
walk_decl(self, decl);
}
fn visit_expr(&mut self, expr: &'v Expr) {
if self.state == VarState::DontWarn || expr == self.end_expr {
self.done = true;
}
if self.state == VarState::IncrOnce || self.done {
return;
}
if var_def_id(self.cx, expr) == Some(self.var_id) {
if let Some(parent) = get_parent_expr(self.cx, expr) {
match parent.node {
ExprAssignOp(_, ref lhs, _) if lhs.id == expr.id => {
self.state = VarState::DontWarn;
},
ExprAssign(ref lhs, ref rhs) if lhs.id == expr.id => {
self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
VarState::Warn
} else {
VarState::DontWarn
}},
ExprAddrOf(mutability,_) if mutability == MutMutable => self.state = VarState::DontWarn,
_ => ()
}
}
}
else if is_loop(expr) {
self.state = VarState::DontWarn;
self.done = true;
return;
}
else if is_conditional(expr) {
self.depth += 1;
walk_expr(self, expr);
self.depth -= 1;
return;
}
walk_expr(self, expr);
}
}
fn var_def_id(cx: &LateContext, expr: &Expr) -> Option<NodeId> {
if let Some(path_res) = cx.tcx.def_map.borrow().get(&expr.id) {
if let DefLocal(node_id) = path_res.base_def {
return Some(node_id)
}
}
None
}
fn is_loop(expr: &Expr) -> bool {
match expr.node {
ExprLoop(..) | ExprWhile(..) => true,
_ => false
}
}
fn is_conditional(expr: &Expr) -> bool {
match expr.node {
ExprIf(..) | ExprMatch(..) => true,
_ => false
}
}