use reexport::*;
use rustc::hir::*;
use rustc::hir::def::Def;
use rustc::hir::def_id::DefId;
use rustc::hir::intravisit::{Visitor, walk_expr, walk_block, walk_decl};
use rustc::hir::map::Node::NodeBlock;
use rustc::lint::*;
use rustc::middle::const_val::ConstVal;
use rustc::middle::region::CodeExtent;
use rustc::ty;
use rustc_const_eval::EvalHint::ExprTypeChecked;
use rustc_const_eval::eval_const_expr_partial;
use std::collections::HashMap;
use syntax::ast;
use utils::sugg;
use utils::{snippet, span_lint, get_parent_expr, match_trait_method, match_type, multispan_sugg, in_external_macro,
span_help_and_lint, is_integer_literal, get_enclosing_block, span_lint_and_then, higher,
walk_ptrs_ty};
use utils::paths;
/// **What it does:** Checks for looping over the range of `0..len` of some
/// collection just to get the values by index.
///
/// **Why is this bad?** Just iterating the collection itself makes the intent
/// more clear and is probably faster.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for i in 0..vec.len() {
/// println!("{}", vec[i]);
/// }
/// ```
declare_lint! {
pub NEEDLESS_RANGE_LOOP,
Warn,
"for-looping over a range of indices where an iterator over items would do"
}
/// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
/// suggests the latter.
///
/// **Why is this bad?** Readability.
///
/// **Known problems:** False negatives. We currently only warn on some known
/// types.
///
/// **Example:**
/// ```rust
/// // with `y` a `Vec` or slice:
/// for x in y.iter() { .. }
/// ```
declare_lint! {
pub EXPLICIT_ITER_LOOP,
Warn,
"for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
}
/// **What it does:** Checks for loops on `x.next()`.
///
/// **Why is this bad?** `next()` returns either `Some(value)` if there was a
/// value, or `None` otherwise. The insidious thing is that `Option<_>`
/// implements `IntoIterator`, so that possibly one value will be iterated,
/// leading to some hard to find bugs. No one will want to write such code
/// [except to win an Underhanded Rust
/// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for x in y.next() { .. }
/// ```
declare_lint! {
pub ITER_NEXT_LOOP,
Warn,
"for-looping over `_.next()` which is probably not intended"
}
/// **What it does:** Checks for `for` loops over `Option` values.
///
/// **Why is this bad?** Readability. This is more clearly expressed as an `if let`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for x in option { .. }
/// ```
///
/// This should be
/// ```rust
/// if let Some(x) = option { .. }
/// ```
declare_lint! {
pub FOR_LOOP_OVER_OPTION,
Warn,
"for-looping over an `Option`, which is more clearly expressed as an `if let`"
}
/// **What it does:** Checks for `for` loops over `Result` values.
///
/// **Why is this bad?** Readability. This is more clearly expressed as an `if let`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for x in result { .. }
/// ```
///
/// This should be
/// ```rust
/// if let Ok(x) = result { .. }
/// ```
declare_lint! {
pub FOR_LOOP_OVER_RESULT,
Warn,
"for-looping over a `Result`, which is more clearly expressed as an `if let`"
}
/// **What it does:** Detects `loop + match` combinations that are easier
/// written as a `while let` loop.
///
/// **Why is this bad?** The `while let` loop is usually shorter and more readable.
///
/// **Known problems:** Sometimes the wrong binding is displayed (#383).
///
/// **Example:**
/// ```rust
/// loop {
/// let x = match y {
/// Some(x) => x,
/// None => break,
/// }
/// // .. do something with x
/// }
/// // is easier written as
/// while let Some(x) = y {
/// // .. do something with x
/// }
/// ```
declare_lint! {
pub WHILE_LET_LOOP,
Warn,
"`loop { if let { ... } else break }`, which can be written as a `while let` loop"
}
/// **What it does:** Checks for using `collect()` on an iterator without using
/// the result.
///
/// **Why is this bad?** It is more idiomatic to use a `for` loop over the
/// iterator instead.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
/// ```
declare_lint! {
pub UNUSED_COLLECT,
Warn,
"`collect()`ing an iterator without using the result; this is usually better \
written as a for loop"
}
/// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
/// are constant and `x` is greater or equal to `y`, unless the range is
/// reversed or has a negative `.step_by(_)`.
///
/// **Why is it bad?** Such loops will either be skipped or loop until
/// wrap-around (in debug code, this may `panic!()`). Both options are probably
/// not intended.
///
/// **Known problems:** The lint cannot catch loops over dynamically defined
/// ranges. Doing this would require simulating all possible inputs and code
/// paths through the program, which would be complex and error-prone.
///
/// **Example:**
/// ```rust
/// for x in 5..10-5 { .. } // oops, stray `-`
/// ```
declare_lint! {
pub REVERSE_RANGE_LOOP,
Warn,
"iteration over an empty range, such as `10..0` or `5..5`"
}
/// **What it does:** Checks `for` loops over slices with an explicit counter
/// and suggests the use of `.enumerate()`.
///
/// **Why is it bad?** Not only is the version using `.enumerate()` more
/// readable, the compiler is able to remove bounds checks which can lead to
/// faster code in some instances.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for i in 0..v.len() { foo(v[i]);
/// for i in 0..v.len() { bar(i, v[i]); }
/// ```
declare_lint! {
pub EXPLICIT_COUNTER_LOOP,
Warn,
"for-looping with an explicit counter when `_.enumerate()` would do"
}
/// **What it does:** Checks for empty `loop` expressions.
///
/// **Why is this bad?** Those busy loops burn CPU cycles without doing
/// anything. Think of the environment and either block on something or at least
/// make the thread sleep for some microseconds.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// loop {}
/// ```
declare_lint! {
pub EMPTY_LOOP,
Warn,
"empty `loop {}`, which should block or sleep"
}
/// **What it does:** Checks for `while let` expressions on iterators.
///
/// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
/// the intent better.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// while let Some(val) = iter() { .. }
/// ```
declare_lint! {
pub WHILE_LET_ON_ITERATOR,
Warn,
"using a while-let loop instead of a for loop on an iterator"
}
/// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
/// ignoring either the keys or values.
///
/// **Why is this bad?** Readability. There are `keys` and `values` methods that
/// can be used to express that don't need the values or keys.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for (k, _) in &map { .. }
/// ```
///
/// could be replaced by
///
/// ```rust
/// for k in map.keys() { .. }
/// ```
declare_lint! {
pub FOR_KV_MAP,
Warn,
"looping on a map using `iter` when `keys` or `values` would do"
}
#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
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,
EMPTY_LOOP,
WHILE_LET_ON_ITERATOR,
FOR_KV_MAP)
}
}
impl LateLintPass for Pass {
fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
if let Some((pat, arg, body)) = higher::for_loop(expr) {
check_for_loop(cx, pat, arg, body, expr);
}
// check for `loop { if let {} else break }` that could be `while let`
// (also matches an explicit "match" instead of "if let")
// (even if the "match" or "if let" is used for declaration)
if let ExprLoop(ref block, _) = expr.node {
// also check for empty `loop {}` statements
if block.stmts.is_empty() && block.expr.is_none() {
span_lint(cx,
EMPTY_LOOP,
expr.span,
"empty `loop {}` detected. You may want to either use `panic!()` or add \
`std::thread::sleep(..);` to the loop body.");
}
// extract the expression from the first statement (if any) in a block
let inner_stmt_expr = extract_expr_from_first_stmt(block);
// or extract the first expression (if any) from the block
if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
if let ExprMatch(ref matchexpr, ref arms, ref source) = inner.node {
// ensure "if let" compatible match structure
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;
}
// NOTE: we used to make build a body here instead of using
// ellipsis, this was removed because:
// 1) it was ugly with big bodies;
// 2) it was not indented properly;
// 3) it wasn’t very smart (see #675).
span_lint_and_then(cx,
WHILE_LET_LOOP,
expr.span,
"this loop could be written as a `while let` loop",
|db| {
let sug = format!("while let {} = {} {{ .. }}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, matchexpr.span, ".."));
db.span_suggestion(expr.span, "try", sug);
});
}
}
_ => (),
}
}
}
}
if let ExprMatch(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
let pat = &arms[0].pats[0].node;
if let (&PatKind::TupleStruct(ref path, ref pat_args, _),
&ExprMethodCall(method_name, _, ref method_args)) = (pat, &match_expr.node) {
let iter_expr = &method_args[0];
if let Some(lhs_constructor) = path.segments.last() {
if method_name.node.as_str() == "next" &&
match_trait_method(cx, match_expr, &paths::ITERATOR) &&
lhs_constructor.name.as_str() == "Some" &&
!is_iterator_used_after_while_let(cx, iter_expr) {
let iterator = snippet(cx, method_args[0].span, "_");
let loop_var = snippet(cx, pat_args[0].span, "_");
span_lint_and_then(cx,
WHILE_LET_ON_ITERATOR,
expr.span,
"this loop could be written as a `for` loop",
|db| {
db.span_suggestion(expr.span,
"try",
format!("for {} in {} {{ .. }}", loop_var, iterator));
});
}
}
}
}
}
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.as_str() == "collect" &&
match_trait_method(cx, expr, &paths::ITERATOR) {
span_lint(cx,
UNUSED_COLLECT,
expr.span,
"you are collect()ing an iterator and throwing away the result. \
Consider using an explicit for loop to exhaust the iterator");
}
}
}
}
}
fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
check_for_loop_range(cx, pat, arg, body, expr);
check_for_loop_reverse_range(cx, arg, expr);
check_for_loop_arg(cx, pat, arg, expr);
check_for_loop_explicit_counter(cx, arg, body, expr);
check_for_loop_over_map_kv(cx, pat, arg, body, expr);
}
/// Check for looping over a range and then indexing a sequence with it.
/// The iteratee must be a range literal.
fn check_for_loop_range(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
if let Some(higher::Range { start: Some(start), ref end, limits }) = higher::range(arg) {
// the var must be a single name
if let PatKind::Binding(_, ref ident, _) = pat.node {
let mut visitor = VarVisitor {
cx: cx,
var: cx.tcx.expect_def(pat.id).def_id(),
indexed: HashMap::new(),
nonindex: false,
};
walk_expr(&mut visitor, body);
// linting condition: we only indexed one variable
if visitor.indexed.len() == 1 {
let (indexed, indexed_extent) = visitor.indexed
.into_iter()
.next()
.unwrap_or_else(|| unreachable!() /* len == 1 */);
// ensure that the indexed variable was declared before the loop, see #601
if let Some(indexed_extent) = indexed_extent {
let pat_extent = cx.tcx.region_maps.var_scope(pat.id);
if cx.tcx.region_maps.is_subscope_of(indexed_extent, pat_extent) {
return;
}
}
let starts_at_zero = is_integer_literal(start, 0);
let skip = if starts_at_zero {
"".to_owned()
} else {
format!(".skip({})", snippet(cx, start.span, ".."))
};
let take = if let Some(end) = *end {
if is_len_call(end, &indexed) {
"".to_owned()
} else {
match limits {
ast::RangeLimits::Closed => {
let end = sugg::Sugg::hir(cx, end, "<count>");
format!(".take({})", end + sugg::ONE)
}
ast::RangeLimits::HalfOpen => {
format!(".take({})", snippet(cx, end.span, ".."))
}
}
}
} else {
"".to_owned()
};
if visitor.nonindex {
span_lint_and_then(cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is used to index `{}`", ident.node, indexed),
|db| {
multispan_sugg(db, "consider using an iterator".to_string(), &[
(pat.span, &format!("({}, <item>)", ident.node)),
(arg.span, &format!("{}.iter().enumerate(){}{}", indexed, take, skip)),
]);
});
} else {
let repl = if starts_at_zero && take.is_empty() {
format!("&{}", indexed)
} else {
format!("{}.iter(){}{}", indexed, take, skip)
};
span_lint_and_then(cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is only used to index `{}`.", ident.node, indexed),
|db| {
multispan_sugg(db, "consider using an iterator".to_string(), &[
(pat.span, "<item>"),
(arg.span, &repl),
]);
});
}
}
}
}
}
fn is_len_call(expr: &Expr, var: &Name) -> bool {
if_let_chain! {[
let ExprMethodCall(method, _, ref len_args) = expr.node,
len_args.len() == 1,
method.node.as_str() == "len",
let ExprPath(_, ref path) = len_args[0].node,
path.segments.len() == 1,
&path.segments[0].name == var
], {
return true;
}}
false
}
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 Some(higher::Range { start: Some(start), end: Some(end), limits }) = higher::range(arg) {
// ...and both sides are compile-time constant integers...
if let Ok(start_idx) = eval_const_expr_partial(cx.tcx, start, ExprTypeChecked, None) {
if let Ok(end_idx) = eval_const_expr_partial(cx.tcx, end, ExprTypeChecked, None) {
// ...and the start index is greater than the end 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.
let (sup, eq) = match (start_idx, end_idx) {
(ConstVal::Integral(start_idx), ConstVal::Integral(end_idx)) => {
(start_idx > end_idx, start_idx == end_idx)
}
_ => (false, false),
};
if sup {
let start_snippet = snippet(cx, start.span, "_");
let end_snippet = snippet(cx, end.span, "_");
let dots = if limits == ast::RangeLimits::Closed {
"..."
} else {
".."
};
span_lint_and_then(cx,
REVERSE_RANGE_LOOP,
expr.span,
"this range is empty so this for loop will never run",
|db| {
db.span_suggestion(arg.span,
"consider using the following if \
you are attempting to iterate \
over this range in reverse",
format!("({end}{dots}{start}).rev()",
end=end_snippet,
dots=dots,
start=start_snippet));
});
} else if eq && limits != ast::RangeLimits::Closed {
// if they are equal, it's also problematic - this loop
// will never run.
span_lint(cx,
REVERSE_RANGE_LOOP,
expr.span,
"this range is empty so this for loop will never run");
}
}
}
}
}
fn check_for_loop_arg(cx: &LateContext, pat: &Pat, arg: &Expr, expr: &Expr) {
let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
if let ExprMethodCall(ref method, _, ref args) = arg.node {
// just the receiver, no arguments
if args.len() == 1 {
let method_name = method.node;
// check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
if method_name.as_str() == "iter" || method_name.as_str() == "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.as_str() == "iter_mut" {
"mut "
} else {
""
},
object,
object,
method_name));
}
} else if method_name.as_str() == "next" && match_trait_method(cx, arg, &paths::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");
next_loop_linted = true;
}
}
}
if !next_loop_linted {
check_arg_type(cx, pat, arg);
}
}
/// Check for `for` loops over `Option`s and `Results`
fn check_arg_type(cx: &LateContext, pat: &Pat, arg: &Expr) {
let ty = cx.tcx.expr_ty(arg);
if match_type(cx, ty, &paths::OPTION) {
span_help_and_lint(cx,
FOR_LOOP_OVER_OPTION,
arg.span,
&format!("for loop over `{0}`, which is an `Option`. This is more readably written as an \
`if let` statement.",
snippet(cx, arg.span, "_")),
&format!("consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
snippet(cx, pat.span, "_"),
snippet(cx, arg.span, "_")));
} else if match_type(cx, ty, &paths::RESULT) {
span_help_and_lint(cx,
FOR_LOOP_OVER_RESULT,
arg.span,
&format!("for loop over `{0}`, which is a `Result`. This is more readably written as an \
`if let` statement.",
snippet(cx, arg.span, "_")),
&format!("consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
snippet(cx, pat.span, "_"),
snippet(cx, arg.span, "_")));
}
}
fn check_for_loop_explicit_counter(cx: &LateContext, arg: &Expr, body: &Expr, expr: &Expr) {
// Look for variables that are incremented once per loop iteration.
let mut visitor = IncrementVisitor {
cx: cx,
states: HashMap::new(),
depth: 0,
done: false,
};
walk_expr(&mut visitor, body);
// For each candidate, check the parent block to see if
// it's initialized to zero at the start of the loop.
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,
state: VarState::IncrOnce,
name: None,
depth: 0,
past_loop: 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, "_")));
}
}
}
}
}
}
/// Check for the `FOR_KV_MAP` lint.
fn check_for_loop_over_map_kv(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
let pat_span = pat.span;
if let PatKind::Tuple(ref pat, _) = pat.node {
if pat.len() == 2 {
let (new_pat_span, kind) = match (&pat[0].node, &pat[1].node) {
(key, _) if pat_is_wild(key, body) => (pat[1].span, "value"),
(_, value) if pat_is_wild(value, body) => (pat[0].span, "key"),
_ => return,
};
let (arg_span, arg) = match arg.node {
ExprAddrOf(MutImmutable, ref expr) => (arg.span, &**expr),
ExprAddrOf(MutMutable, _) => return, // for _ in &mut _, there is no {values,keys}_mut method
_ => (arg.span, arg),
};
let ty = walk_ptrs_ty(cx.tcx.expr_ty(arg));
if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
span_lint_and_then(cx,
FOR_KV_MAP,
expr.span,
&format!("you seem to want to iterate on a map's {}s", kind),
|db| {
let map = sugg::Sugg::hir(cx, arg, "map");
multispan_sugg(db, "use the corresponding method".into(), &[
(pat_span, &snippet(cx, new_pat_span, kind)),
(arg_span, &format!("{}.{}s()", map.maybe_par(), kind)),
]);
});
}
}
}
}
/// Return true if the pattern is a `PatWild` or an ident prefixed with `'_'`.
fn pat_is_wild(pat: &PatKind, body: &Expr) -> bool {
match *pat {
PatKind::Wild => true,
PatKind::Binding(_, ident, None) if ident.node.as_str().starts_with('_') => {
let mut visitor = UsedVisitor {
var: ident.node,
used: false,
};
walk_expr(&mut visitor, body);
!visitor.used
}
_ => false,
}
}
struct UsedVisitor {
var: ast::Name, // var to look for
used: bool, // has the var been used otherwise?
}
impl<'a> Visitor<'a> for UsedVisitor {
fn visit_expr(&mut self, expr: &Expr) {
if let ExprPath(None, ref path) = expr.node {
if path.segments.len() == 1 && path.segments[0].name == self.var {
self.used = true;
return;
}
}
walk_expr(self, expr);
}
}
struct VarVisitor<'v, 't: 'v> {
cx: &'v LateContext<'v, 't>, // context reference
var: DefId, // var name to look for as index
indexed: HashMap<Name, Option<CodeExtent>>, // indexed variables, the extent is None for global
nonindex: bool, // has the var been used otherwise?
}
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 && self.cx.tcx.expect_def(expr.id).def_id() == self.var {
// we are referencing our variable! now check if it's as an index
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
], {
let def_map = self.cx.tcx.def_map.borrow();
if let Some(def) = def_map.get(&seqexpr.id) {
match def.base_def {
Def::Local(..) | Def::Upvar(..) => {
let extent = self.cx.tcx.region_maps.var_scope(def.base_def.var_id());
self.indexed.insert(seqvar.segments[0].name, Some(extent));
return; // no need to walk further
}
Def::Static(..) | Def::Const(..) => {
self.indexed.insert(seqvar.segments[0].name, None);
return; // no need to walk further
}
_ => (),
}
}
}}
// we are not indexing anything, record that
self.nonindex = true;
return;
}
}
walk_expr(self, expr);
}
}
fn is_iterator_used_after_while_let(cx: &LateContext, iter_expr: &Expr) -> bool {
let def_id = match var_def_id(cx, iter_expr) {
Some(id) => id,
None => return false,
};
let mut visitor = VarUsedAfterLoopVisitor {
cx: cx,
def_id: def_id,
iter_expr_id: iter_expr.id,
past_while_let: false,
var_used_after_while_let: false,
};
if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
walk_block(&mut visitor, enclosing_block);
}
visitor.var_used_after_while_let
}
struct VarUsedAfterLoopVisitor<'v, 't: 'v> {
cx: &'v LateContext<'v, 't>,
def_id: NodeId,
iter_expr_id: NodeId,
past_while_let: bool,
var_used_after_while_let: bool,
}
impl<'v, 't> Visitor<'v> for VarUsedAfterLoopVisitor<'v, 't> {
fn visit_expr(&mut self, expr: &'v Expr) {
if self.past_while_let {
if Some(self.def_id) == var_def_id(self.cx, expr) {
self.var_used_after_while_let = true;
}
} else if self.iter_expr_id == expr.id {
self.past_while_let = true;
}
walk_expr(self, expr);
}
}
/// Return true if the type of expr is one that provides `IntoIterator` impls
/// for `&T` and `&mut T`, such as `Vec`.
#[cfg_attr(rustfmt, rustfmt_skip)]
fn is_ref_iterable_type(cx: &LateContext, e: &Expr) -> bool {
// no walk_ptrs_ty: calling iter() on a reference can make sense because it
// will allow further borrows afterwards
let ty = cx.tcx.expr_ty(e);
is_iterable_array(ty) ||
match_type(cx, ty, &paths::VEC) ||
match_type(cx, ty, &paths::LINKED_LIST) ||
match_type(cx, ty, &paths::HASHMAP) ||
match_type(cx, ty, &paths::HASHSET) ||
match_type(cx, ty, &paths::VEC_DEQUE) ||
match_type(cx, ty, &paths::BINARY_HEAP) ||
match_type(cx, ty, &paths::BTREEMAP) ||
match_type(cx, ty, &paths::BTREESET)
}
fn is_iterable_array(ty: ty::Ty) -> bool {
// IntoIterator is currently only implemented for array sizes <= 32 in rustc
match ty.sty {
ty::TyArray(_, 0...32) => true,
_ => false,
}
}
/// If a block begins with a statement (possibly a `let` binding) and has an expression, return it.
fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
if block.stmts.is_empty() {
return None;
}
if let StmtDecl(ref decl, _) = block.stmts[0].node {
if let DeclLocal(ref local) = decl.node {
if let Some(ref expr) = local.init {
Some(expr)
} else {
None
}
} else {
None
}
} else {
None
}
}
/// If a block begins with an expression (with or without semicolon), return it.
fn extract_first_expr(block: &Block) -> Option<&Expr> {
match block.expr {
Some(ref expr) if block.stmts.is_empty() => Some(expr),
None if !block.stmts.is_empty() => {
match block.stmts[0].node {
StmtExpr(ref expr, _) | StmtSemi(ref expr, _) => Some(expr),
StmtDecl(..) => None,
}
}
_ => None,
}
}
/// Return true if expr contains a single break expr (maybe within a block).
fn is_break_expr(expr: &Expr) -> bool {
match expr.node {
ExprBreak(None) => true,
ExprBlock(ref b) => {
match extract_first_expr(b) {
Some(subexpr) => is_break_expr(subexpr),
None => false,
}
}
_ => false,
}
}
// To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
// incremented exactly once in the loop body, and initialized to zero
// at the start of the loop.
#[derive(PartialEq)]
enum VarState {
Initial, // Not examined yet
IncrOnce, // Incremented exactly once, may be a loop counter
Declared, // Declared but not (yet) initialized to zero
Warn,
DontWarn,
}
/// Scan a for loop for variables that are incremented exactly once.
struct IncrementVisitor<'v, 't: 'v> {
cx: &'v LateContext<'v, 't>, // context reference
states: HashMap<NodeId, VarState>, // incremented variables
depth: u32, // depth of conditional expressions
done: bool,
}
impl<'v, 't> Visitor<'v> for IncrementVisitor<'v, 't> {
fn visit_expr(&mut self, expr: &'v Expr) {
if self.done {
return;
}
// If node is a variable
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 {
// Assigned some other value
*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);
}
}
/// Check whether a variable is initialized to zero at the start of a loop.
struct InitializeVisitor<'v, 't: 'v> {
cx: &'v LateContext<'v, 't>, // context reference
end_expr: &'v Expr, // the for loop. Stop scanning here.
var_id: NodeId,
state: VarState,
name: Option<Name>,
depth: u32, // depth of conditional expressions
past_loop: bool,
}
impl<'v, 't> Visitor<'v> for InitializeVisitor<'v, 't> {
fn visit_decl(&mut self, decl: &'v Decl) {
// Look for declarations of the variable
if let DeclLocal(ref local) = decl.node {
if local.pat.id == self.var_id {
if let PatKind::Binding(_, ref ident, _) = local.pat.node {
self.name = Some(ident.node);
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 {
return;
}
if expr == self.end_expr {
self.past_loop = true;
return;
}
// No need to visit expressions before the variable is
// declared
if self.state == VarState::IncrOnce {
return;
}
// If node is the desired variable, see how it's used
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,
_ => (),
}
}
if self.past_loop {
self.state = VarState::DontWarn;
return;
}
} else if !self.past_loop && is_loop(expr) {
self.state = VarState::DontWarn;
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 Def::Local(_, 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,
}
}