1525 lines
52 KiB
Rust
1525 lines
52 KiB
Rust
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, walk_pat, walk_stmt, NestedVisitorMap};
|
||
use rustc::hir::map::Node::{NodeBlock, NodeExpr, NodeStmt};
|
||
use rustc::lint::*;
|
||
use rustc::middle::const_val::ConstVal;
|
||
use rustc::middle::region::CodeExtent;
|
||
use rustc::ty::{self, Ty};
|
||
use rustc::ty::subst::{Subst, Substs};
|
||
use rustc_const_eval::ConstContext;
|
||
use std::collections::{HashMap, HashSet};
|
||
use syntax::ast;
|
||
use utils::sugg;
|
||
|
||
use utils::{snippet, span_lint, get_parent_expr, match_trait_method, match_type, multispan_sugg, in_external_macro,
|
||
is_refutable, span_help_and_lint, is_integer_literal, get_enclosing_block, span_lint_and_then, higher,
|
||
last_path_segment, span_lint_and_sugg};
|
||
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 `y.into_iter()` where `y` will do, and
|
||
/// suggests the latter.
|
||
///
|
||
/// **Why is this bad?** Readability.
|
||
///
|
||
/// **Known problems:** None
|
||
///
|
||
/// **Example:**
|
||
/// ```rust
|
||
/// // with `y` a `Vec` or slice:
|
||
/// for x in y.into_iter() { .. }
|
||
/// ```
|
||
declare_lint! {
|
||
pub EXPLICIT_INTO_ITER_LOOP,
|
||
Warn,
|
||
"for-looping over `_.into_iter()` when `_` 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"
|
||
}
|
||
|
||
/// **What it does:** Checks for loops that will always `break`, `return` or
|
||
/// `continue` an outer loop.
|
||
///
|
||
/// **Why is this bad?** This loop never loops, all it does is obfuscating the
|
||
/// code.
|
||
///
|
||
/// **Known problems:** None
|
||
///
|
||
/// **Example:**
|
||
/// ```rust
|
||
/// loop { ..; break; }
|
||
/// ```
|
||
declare_lint! {
|
||
pub NEVER_LOOP,
|
||
Warn,
|
||
"any loop that will always `break` or `return`"
|
||
}
|
||
|
||
#[derive(Copy, Clone)]
|
||
pub struct Pass;
|
||
|
||
impl LintPass for Pass {
|
||
fn get_lints(&self) -> LintArray {
|
||
lint_array!(
|
||
NEEDLESS_RANGE_LOOP,
|
||
EXPLICIT_ITER_LOOP,
|
||
EXPLICIT_INTO_ITER_LOOP,
|
||
ITER_NEXT_LOOP,
|
||
FOR_LOOP_OVER_RESULT,
|
||
FOR_LOOP_OVER_OPTION,
|
||
WHILE_LET_LOOP,
|
||
UNUSED_COLLECT,
|
||
REVERSE_RANGE_LOOP,
|
||
EXPLICIT_COUNTER_LOOP,
|
||
EMPTY_LOOP,
|
||
WHILE_LET_ON_ITERATOR,
|
||
FOR_KV_MAP,
|
||
NEVER_LOOP
|
||
)
|
||
}
|
||
}
|
||
|
||
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
|
||
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
|
||
if let Some((pat, arg, body)) = higher::for_loop(expr) {
|
||
check_for_loop(cx, pat, arg, body, expr);
|
||
}
|
||
|
||
// check for never_loop
|
||
match expr.node {
|
||
ExprWhile(_, ref block, _) |
|
||
ExprLoop(ref block, _, _) => {
|
||
if never_loop(block, &expr.id) {
|
||
span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops");
|
||
}
|
||
},
|
||
_ => (),
|
||
}
|
||
|
||
// 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, _, LoopSource::Loop) = 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_sugg(
|
||
cx,
|
||
WHILE_LET_LOOP,
|
||
expr.span,
|
||
"this loop could be written as a `while let` loop",
|
||
"try",
|
||
format!(
|
||
"while let {} = {} {{ .. }}",
|
||
snippet(cx, arms[0].pats[0].span, ".."),
|
||
snippet(cx, matchexpr.span, "..")
|
||
),
|
||
);
|
||
}
|
||
},
|
||
_ => (),
|
||
}
|
||
}
|
||
}
|
||
}
|
||
if let ExprMatch(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
|
||
let pat = &arms[0].pats[0].node;
|
||
if let (&PatKind::TupleStruct(ref qpath, ref pat_args, _),
|
||
&ExprMethodCall(ref method_path, _, ref method_args)) = (pat, &match_expr.node)
|
||
{
|
||
let iter_expr = &method_args[0];
|
||
let lhs_constructor = last_path_segment(qpath);
|
||
if method_path.name == "next" && match_trait_method(cx, match_expr, &paths::ITERATOR) &&
|
||
lhs_constructor.name == "Some" && !is_refutable(cx, &pat_args[0]) &&
|
||
!is_iterator_used_after_while_let(cx, iter_expr) &&
|
||
!is_nested(cx, expr, &method_args[0])
|
||
{
|
||
let iterator = snippet(cx, method_args[0].span, "_");
|
||
let loop_var = snippet(cx, pat_args[0].span, "_");
|
||
span_lint_and_sugg(
|
||
cx,
|
||
WHILE_LET_ON_ITERATOR,
|
||
expr.span,
|
||
"this loop could be written as a `for` loop",
|
||
"try",
|
||
format!("for {} in {} {{ .. }}", loop_var, iterator),
|
||
);
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
|
||
if let StmtSemi(ref expr, _) = stmt.node {
|
||
if let ExprMethodCall(ref method, _, ref args) = expr.node {
|
||
if args.len() == 1 && method.name == "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 never_loop(block: &Block, id: &NodeId) -> bool {
|
||
!contains_continue_block(block, id) && loop_exit_block(block)
|
||
}
|
||
|
||
fn contains_continue_block(block: &Block, dest: &NodeId) -> bool {
|
||
block.stmts.iter().any(|e| contains_continue_stmt(e, dest)) ||
|
||
block.expr.as_ref().map_or(
|
||
false,
|
||
|e| contains_continue_expr(e, dest),
|
||
)
|
||
}
|
||
|
||
fn contains_continue_stmt(stmt: &Stmt, dest: &NodeId) -> bool {
|
||
match stmt.node {
|
||
StmtSemi(ref e, _) |
|
||
StmtExpr(ref e, _) => contains_continue_expr(e, dest),
|
||
StmtDecl(ref d, _) => contains_continue_decl(d, dest),
|
||
}
|
||
}
|
||
|
||
fn contains_continue_decl(decl: &Decl, dest: &NodeId) -> bool {
|
||
match decl.node {
|
||
DeclLocal(ref local) => {
|
||
local.init.as_ref().map_or(
|
||
false,
|
||
|e| contains_continue_expr(e, dest),
|
||
)
|
||
},
|
||
_ => false,
|
||
}
|
||
}
|
||
|
||
fn contains_continue_expr(expr: &Expr, dest: &NodeId) -> bool {
|
||
match expr.node {
|
||
ExprRet(Some(ref e)) |
|
||
ExprBox(ref e) |
|
||
ExprUnary(_, ref e) |
|
||
ExprCast(ref e, _) |
|
||
ExprType(ref e, _) |
|
||
ExprField(ref e, _) |
|
||
ExprTupField(ref e, _) |
|
||
ExprAddrOf(_, ref e) |
|
||
ExprRepeat(ref e, _) => contains_continue_expr(e, dest),
|
||
ExprArray(ref es) |
|
||
ExprMethodCall(_, _, ref es) |
|
||
ExprTup(ref es) => es.iter().any(|e| contains_continue_expr(e, dest)),
|
||
ExprCall(ref e, ref es) => {
|
||
contains_continue_expr(e, dest) || es.iter().any(|e| contains_continue_expr(e, dest))
|
||
},
|
||
ExprBinary(_, ref e1, ref e2) |
|
||
ExprAssign(ref e1, ref e2) |
|
||
ExprAssignOp(_, ref e1, ref e2) |
|
||
ExprIndex(ref e1, ref e2) => [e1, e2].iter().any(|e| contains_continue_expr(e, dest)),
|
||
ExprIf(ref e, ref e2, ref e3) => {
|
||
[e, e2].iter().chain(e3.as_ref().iter()).any(|e| {
|
||
contains_continue_expr(e, dest)
|
||
})
|
||
},
|
||
ExprWhile(ref e, ref b, _) => contains_continue_expr(e, dest) || contains_continue_block(b, dest),
|
||
ExprMatch(ref e, ref arms, _) => {
|
||
contains_continue_expr(e, dest) || arms.iter().any(|a| contains_continue_expr(&a.body, dest))
|
||
},
|
||
ExprBlock(ref block) => contains_continue_block(block, dest),
|
||
ExprStruct(_, _, ref base) => {
|
||
base.as_ref().map_or(
|
||
false,
|
||
|e| contains_continue_expr(e, dest),
|
||
)
|
||
},
|
||
ExprAgain(d) => d.target_id.opt_id().map_or(false, |id| id == *dest),
|
||
_ => false,
|
||
}
|
||
}
|
||
|
||
fn loop_exit_block(block: &Block) -> bool {
|
||
block.stmts.iter().any(|e| loop_exit_stmt(e)) || block.expr.as_ref().map_or(false, |e| loop_exit_expr(e))
|
||
}
|
||
|
||
fn loop_exit_stmt(stmt: &Stmt) -> bool {
|
||
match stmt.node {
|
||
StmtSemi(ref e, _) |
|
||
StmtExpr(ref e, _) => loop_exit_expr(e),
|
||
StmtDecl(ref d, _) => loop_exit_decl(d),
|
||
}
|
||
}
|
||
|
||
fn loop_exit_decl(decl: &Decl) -> bool {
|
||
match decl.node {
|
||
DeclLocal(ref local) => local.init.as_ref().map_or(false, |e| loop_exit_expr(e)),
|
||
_ => false,
|
||
}
|
||
}
|
||
|
||
fn loop_exit_expr(expr: &Expr) -> bool {
|
||
match expr.node {
|
||
ExprBox(ref e) |
|
||
ExprUnary(_, ref e) |
|
||
ExprCast(ref e, _) |
|
||
ExprType(ref e, _) |
|
||
ExprField(ref e, _) |
|
||
ExprTupField(ref e, _) |
|
||
ExprAddrOf(_, ref e) |
|
||
ExprRepeat(ref e, _) => loop_exit_expr(e),
|
||
ExprArray(ref es) |
|
||
ExprMethodCall(_, _, ref es) |
|
||
ExprTup(ref es) => es.iter().any(|e| loop_exit_expr(e)),
|
||
ExprCall(ref e, ref es) => loop_exit_expr(e) || es.iter().any(|e| loop_exit_expr(e)),
|
||
ExprBinary(_, ref e1, ref e2) |
|
||
ExprAssign(ref e1, ref e2) |
|
||
ExprAssignOp(_, ref e1, ref e2) |
|
||
ExprIndex(ref e1, ref e2) => [e1, e2].iter().any(|e| loop_exit_expr(e)),
|
||
ExprIf(ref e, ref e2, ref e3) => {
|
||
loop_exit_expr(e) || e3.as_ref().map_or(false, |e| loop_exit_expr(e)) && loop_exit_expr(e2)
|
||
},
|
||
ExprWhile(ref e, ref b, _) => loop_exit_expr(e) || loop_exit_block(b),
|
||
ExprMatch(ref e, ref arms, _) => loop_exit_expr(e) || arms.iter().all(|a| loop_exit_expr(&a.body)),
|
||
ExprBlock(ref b) => loop_exit_block(b),
|
||
ExprBreak(_, _) | ExprAgain(_) | ExprRet(_) => true,
|
||
_ => false,
|
||
}
|
||
}
|
||
|
||
fn check_for_loop<'a, 'tcx>(
|
||
cx: &LateContext<'a, 'tcx>,
|
||
pat: &'tcx Pat,
|
||
arg: &'tcx Expr,
|
||
body: &'tcx Expr,
|
||
expr: &'tcx 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<'a, 'tcx>(
|
||
cx: &LateContext<'a, 'tcx>,
|
||
pat: &'tcx Pat,
|
||
arg: &'tcx Expr,
|
||
body: &'tcx Expr,
|
||
expr: &'tcx 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(_, def_id, ref ident, _) = pat.node {
|
||
let mut visitor = VarVisitor {
|
||
cx: cx,
|
||
var: def_id,
|
||
indexed: HashMap::new(),
|
||
referenced: HashSet::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().expect(
|
||
"already checked that we have exactly 1 element",
|
||
);
|
||
|
||
// ensure that the indexed variable was declared before the loop, see #601
|
||
if let Some(indexed_extent) = indexed_extent {
|
||
let parent_id = cx.tcx.hir.get_parent(expr.id);
|
||
let parent_def_id = cx.tcx.hir.local_def_id(parent_id);
|
||
let region_maps = cx.tcx.region_maps(parent_def_id);
|
||
let pat_extent = region_maps.var_scope(pat.id);
|
||
if region_maps.is_subscope_of(indexed_extent, pat_extent) {
|
||
return;
|
||
}
|
||
}
|
||
|
||
// don't lint if the container that is indexed into is also used without
|
||
// indexing
|
||
if visitor.referenced.contains(&indexed) {
|
||
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(),
|
||
vec![(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(),
|
||
vec![(pat.span, "<item>".to_string()), (arg.span, repl)]);
|
||
});
|
||
}
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn is_len_call(expr: &Expr, var: &Name) -> bool {
|
||
if_let_chain! {[
|
||
let ExprMethodCall(ref method, _, ref len_args) = expr.node,
|
||
len_args.len() == 1,
|
||
method.name == "len",
|
||
let ExprPath(QPath::Resolved(_, 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...
|
||
let parent_item = cx.tcx.hir.get_parent(arg.id);
|
||
let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
|
||
let substs = Substs::identity_for_item(cx.tcx, parent_def_id);
|
||
let constcx = ConstContext::new(cx.tcx, cx.param_env.and(substs), cx.tables);
|
||
if let Ok(start_idx) = constcx.eval(start) {
|
||
if let Ok(end_idx) = constcx.eval(end) {
|
||
// ...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 lint_iter_method(cx: &LateContext, args: &[Expr], arg: &Expr, method_name: &str) {
|
||
let object = snippet(cx, args[0].span, "_");
|
||
let muta = if method_name == "iter_mut" {
|
||
"mut "
|
||
} else {
|
||
""
|
||
};
|
||
span_lint_and_sugg(
|
||
cx,
|
||
EXPLICIT_ITER_LOOP,
|
||
arg.span,
|
||
"it is more idiomatic to loop over references to containers instead of using explicit \
|
||
iteration methods",
|
||
"to write this more concisely, try",
|
||
format!("&{}{}", muta, object),
|
||
)
|
||
}
|
||
|
||
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.name.as_str();
|
||
// check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
|
||
if method_name == "iter" || method_name == "iter_mut" {
|
||
if is_ref_iterable_type(cx, &args[0]) {
|
||
lint_iter_method(cx, args, arg, method_name);
|
||
}
|
||
} else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
|
||
let def_id = cx.tables.type_dependent_defs()[arg.hir_id].def_id();
|
||
let substs = cx.tables.node_substs(arg.hir_id);
|
||
let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
|
||
|
||
let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
|
||
assert_eq!(fn_arg_tys.skip_binder().len(), 1);
|
||
if fn_arg_tys.skip_binder()[0].is_region_ptr() {
|
||
lint_iter_method(cx, args, arg, method_name);
|
||
} else {
|
||
let object = snippet(cx, args[0].span, "_");
|
||
span_lint_and_sugg(
|
||
cx,
|
||
EXPLICIT_INTO_ITER_LOOP,
|
||
arg.span,
|
||
"it is more idiomatic to loop over containers instead of using explicit \
|
||
iteration methods`",
|
||
"to write this more concisely, try",
|
||
object.to_string(),
|
||
);
|
||
}
|
||
} else if method_name == "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.tables.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<'a, 'tcx>(
|
||
cx: &LateContext<'a, 'tcx>,
|
||
arg: &'tcx Expr,
|
||
body: &'tcx Expr,
|
||
expr: &'tcx 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.hir;
|
||
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<'a, 'tcx>(
|
||
cx: &LateContext<'a, 'tcx>,
|
||
pat: &'tcx Pat,
|
||
arg: &'tcx Expr,
|
||
body: &'tcx Expr,
|
||
expr: &'tcx Expr,
|
||
) {
|
||
let pat_span = pat.span;
|
||
|
||
if let PatKind::Tuple(ref pat, _) = pat.node {
|
||
if pat.len() == 2 {
|
||
let arg_span = arg.span;
|
||
let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
|
||
ty::TyRef(_, ref tam) => {
|
||
match (&pat[0].node, &pat[1].node) {
|
||
(key, _) if pat_is_wild(key, body) => (pat[1].span, "value", tam.ty, tam.mutbl),
|
||
(_, value) if pat_is_wild(value, body) => (pat[0].span, "key", tam.ty, MutImmutable),
|
||
_ => return,
|
||
}
|
||
},
|
||
_ => return,
|
||
};
|
||
let mutbl = match mutbl {
|
||
MutImmutable => "",
|
||
MutMutable => "_mut",
|
||
};
|
||
let arg = match arg.node {
|
||
ExprAddrOf(_, ref expr) => &**expr,
|
||
_ => 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(),
|
||
vec![(pat_span, snippet(cx, new_pat_span, kind).into_owned()),
|
||
(arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl))]);
|
||
});
|
||
}
|
||
}
|
||
}
|
||
|
||
}
|
||
|
||
/// Return true if the pattern is a `PatWild` or an ident prefixed with `'_'`.
|
||
fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx 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,
|
||
}
|
||
}
|
||
|
||
fn match_var(expr: &Expr, var: Name) -> bool {
|
||
if let ExprPath(QPath::Resolved(None, ref path)) = expr.node {
|
||
if path.segments.len() == 1 && path.segments[0].name == var {
|
||
return true;
|
||
}
|
||
}
|
||
false
|
||
}
|
||
|
||
struct UsedVisitor {
|
||
var: ast::Name, // var to look for
|
||
used: bool, // has the var been used otherwise?
|
||
}
|
||
|
||
impl<'tcx> Visitor<'tcx> for UsedVisitor {
|
||
fn visit_expr(&mut self, expr: &'tcx Expr) {
|
||
if match_var(expr, self.var) {
|
||
self.used = true;
|
||
return;
|
||
}
|
||
walk_expr(self, expr);
|
||
}
|
||
|
||
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
|
||
NestedVisitorMap::None
|
||
}
|
||
}
|
||
|
||
struct VarVisitor<'a, 'tcx: 'a> {
|
||
/// context reference
|
||
cx: &'a LateContext<'a, 'tcx>,
|
||
/// var name to look for as index
|
||
var: DefId,
|
||
/// indexed variables, the extend is `None` for global
|
||
indexed: HashMap<Name, Option<CodeExtent>>,
|
||
/// Any names that are used outside an index operation.
|
||
/// Used to detect things like `&mut vec` used together with `vec[i]`
|
||
referenced: HashSet<Name>,
|
||
/// has the loop variable been used in expressions other than the index of
|
||
/// an index op?
|
||
nonindex: bool,
|
||
}
|
||
|
||
impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
|
||
fn visit_expr(&mut self, expr: &'tcx Expr) {
|
||
if_let_chain! {[
|
||
// an index op
|
||
let ExprIndex(ref seqexpr, ref idx) = expr.node,
|
||
// directly indexing a variable
|
||
let ExprPath(ref qpath) = idx.node,
|
||
let QPath::Resolved(None, ref path) = *qpath,
|
||
path.segments.len() == 1,
|
||
// our variable!
|
||
self.cx.tables.qpath_def(qpath, expr.hir_id).def_id() == self.var,
|
||
// the indexed container is referenced by a name
|
||
let ExprPath(ref seqpath) = seqexpr.node,
|
||
let QPath::Resolved(None, ref seqvar) = *seqpath,
|
||
seqvar.segments.len() == 1,
|
||
], {
|
||
let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
|
||
match def {
|
||
Def::Local(..) | Def::Upvar(..) => {
|
||
let def_id = def.def_id();
|
||
let node_id = self.cx.tcx.hir.as_local_node_id(def_id).expect("local/upvar are local nodes");
|
||
|
||
let parent_id = self.cx.tcx.hir.get_parent(expr.id);
|
||
let parent_def_id = self.cx.tcx.hir.local_def_id(parent_id);
|
||
let extent = self.cx.tcx.region_maps(parent_def_id).var_scope(node_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
|
||
}
|
||
_ => (),
|
||
}
|
||
}}
|
||
|
||
if_let_chain! {[
|
||
// directly indexing a variable
|
||
let ExprPath(ref qpath) = expr.node,
|
||
let QPath::Resolved(None, ref path) = *qpath,
|
||
path.segments.len() == 1,
|
||
], {
|
||
if self.cx.tables.qpath_def(qpath, expr.hir_id).def_id() == self.var {
|
||
// we are not indexing anything, record that
|
||
self.nonindex = true;
|
||
} else {
|
||
// not the correct variable, but still a variable
|
||
self.referenced.insert(path.segments[0].name);
|
||
}
|
||
}}
|
||
|
||
walk_expr(self, expr);
|
||
}
|
||
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
|
||
NestedVisitorMap::None
|
||
}
|
||
}
|
||
|
||
fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx 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<'a, 'tcx: 'a> {
|
||
cx: &'a LateContext<'a, 'tcx>,
|
||
def_id: NodeId,
|
||
iter_expr_id: NodeId,
|
||
past_while_let: bool,
|
||
var_used_after_while_let: bool,
|
||
}
|
||
|
||
impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
|
||
fn visit_expr(&mut self, expr: &'tcx 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);
|
||
}
|
||
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
|
||
NestedVisitorMap::None
|
||
}
|
||
}
|
||
|
||
|
||
/// 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.tables.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) -> 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(dest, _) if dest.ident.is_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<'a, 'tcx: 'a> {
|
||
cx: &'a LateContext<'a, 'tcx>, // context reference
|
||
states: HashMap<NodeId, VarState>, // incremented variables
|
||
depth: u32, // depth of conditional expressions
|
||
done: bool,
|
||
}
|
||
|
||
impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
|
||
fn visit_expr(&mut self, expr: &'tcx 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);
|
||
}
|
||
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
|
||
NestedVisitorMap::None
|
||
}
|
||
}
|
||
|
||
/// Check whether a variable is initialized to zero at the start of a loop.
|
||
struct InitializeVisitor<'a, 'tcx: 'a> {
|
||
cx: &'a LateContext<'a, 'tcx>, // context reference
|
||
end_expr: &'tcx 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<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
|
||
fn visit_decl(&mut self, decl: &'tcx 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: &'tcx 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 nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
|
||
NestedVisitorMap::None
|
||
}
|
||
}
|
||
|
||
fn var_def_id(cx: &LateContext, expr: &Expr) -> Option<NodeId> {
|
||
if let ExprPath(ref qpath) = expr.node {
|
||
let path_res = cx.tables.qpath_def(qpath, expr.hir_id);
|
||
if let Def::Local(def_id) = path_res {
|
||
let node_id = cx.tcx.hir.as_local_node_id(def_id).expect(
|
||
"That DefId should be valid",
|
||
);
|
||
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,
|
||
}
|
||
}
|
||
|
||
fn is_nested(cx: &LateContext, match_expr: &Expr, iter_expr: &Expr) -> bool {
|
||
if_let_chain! {[
|
||
let Some(loop_block) = get_enclosing_block(cx, match_expr.id),
|
||
let Some(map::Node::NodeExpr(loop_expr)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(loop_block.id)),
|
||
], {
|
||
return is_loop_nested(cx, loop_expr, iter_expr)
|
||
}}
|
||
false
|
||
}
|
||
|
||
fn is_loop_nested(cx: &LateContext, loop_expr: &Expr, iter_expr: &Expr) -> bool {
|
||
let mut id = loop_expr.id;
|
||
let iter_name = if let Some(name) = path_name(iter_expr) {
|
||
name
|
||
} else {
|
||
return true;
|
||
};
|
||
loop {
|
||
let parent = cx.tcx.hir.get_parent_node(id);
|
||
if parent == id {
|
||
return false;
|
||
}
|
||
match cx.tcx.hir.find(parent) {
|
||
Some(NodeExpr(expr)) => {
|
||
match expr.node {
|
||
ExprLoop(..) | ExprWhile(..) => {
|
||
return true;
|
||
},
|
||
_ => (),
|
||
}
|
||
},
|
||
Some(NodeBlock(block)) => {
|
||
let mut block_visitor = LoopNestVisitor {
|
||
id: id,
|
||
iterator: iter_name,
|
||
nesting: Unknown,
|
||
};
|
||
walk_block(&mut block_visitor, block);
|
||
if block_visitor.nesting == RuledOut {
|
||
return false;
|
||
}
|
||
},
|
||
Some(NodeStmt(_)) => (),
|
||
_ => {
|
||
return false;
|
||
},
|
||
}
|
||
id = parent;
|
||
}
|
||
}
|
||
|
||
#[derive(PartialEq, Eq)]
|
||
enum Nesting {
|
||
Unknown, // no nesting detected yet
|
||
RuledOut, // the iterator is initialized or assigned within scope
|
||
LookFurther, // no nesting detected, no further walk required
|
||
}
|
||
|
||
use self::Nesting::{Unknown, RuledOut, LookFurther};
|
||
|
||
struct LoopNestVisitor {
|
||
id: NodeId,
|
||
iterator: Name,
|
||
nesting: Nesting,
|
||
}
|
||
|
||
impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
|
||
fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
|
||
if stmt.node.id() == self.id {
|
||
self.nesting = LookFurther;
|
||
} else if self.nesting == Unknown {
|
||
walk_stmt(self, stmt);
|
||
}
|
||
}
|
||
|
||
fn visit_expr(&mut self, expr: &'tcx Expr) {
|
||
if self.nesting != Unknown {
|
||
return;
|
||
}
|
||
if expr.id == self.id {
|
||
self.nesting = LookFurther;
|
||
return;
|
||
}
|
||
match expr.node {
|
||
ExprAssign(ref path, _) |
|
||
ExprAssignOp(_, ref path, _) => {
|
||
if match_var(path, self.iterator) {
|
||
self.nesting = RuledOut;
|
||
}
|
||
},
|
||
_ => walk_expr(self, expr),
|
||
}
|
||
}
|
||
|
||
fn visit_pat(&mut self, pat: &'tcx Pat) {
|
||
if self.nesting != Unknown {
|
||
return;
|
||
}
|
||
if let PatKind::Binding(_, _, span_name, _) = pat.node {
|
||
if self.iterator == span_name.node {
|
||
self.nesting = RuledOut;
|
||
return;
|
||
}
|
||
}
|
||
walk_pat(self, pat)
|
||
}
|
||
|
||
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
|
||
NestedVisitorMap::None
|
||
}
|
||
}
|
||
|
||
fn path_name(e: &Expr) -> Option<Name> {
|
||
if let ExprPath(QPath::Resolved(_, ref path)) = e.node {
|
||
let segments = &path.segments;
|
||
if segments.len() == 1 {
|
||
return Some(segments[0].name);
|
||
}
|
||
};
|
||
None
|
||
}
|