687 lines
30 KiB
Rust
687 lines
30 KiB
Rust
use rustc::lint::*;
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use rustc_front::hir::*;
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use reexport::*;
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use rustc_front::intravisit::{Visitor, walk_expr, walk_block, walk_decl};
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use rustc::middle::ty;
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use rustc::middle::def::DefLocal;
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use consts::{constant_simple, Constant};
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use rustc::front::map::Node::{NodeBlock};
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use std::borrow::Cow;
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use std::collections::{HashSet,HashMap};
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use syntax::ast::Lit_::*;
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use utils::{snippet, span_lint, get_parent_expr, match_trait_method, match_type,
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in_external_macro, expr_block, span_help_and_lint, is_integer_literal,
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get_enclosing_block};
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use utils::{VEC_PATH, LL_PATH};
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/// **What it does:** This lint checks for looping over the range of `0..len` of some collection just to get the values by index. It is `Warn` by default.
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///
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/// **Why is this bad?** Just iterating the collection itself makes the intent more clear and is probably faster.
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///
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/// **Known problems:** None
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///
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/// **Example:**
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/// ```
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/// for i in 0..vec.len() {
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/// println!("{}", vec[i]);
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/// }
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/// ```
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declare_lint!{ pub NEEDLESS_RANGE_LOOP, Warn,
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"for-looping over a range of indices where an iterator over items would do" }
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/// **What it does:** This lint checks for loops on `x.iter()` where `&x` will do, and suggest the latter. It is `Warn` by default.
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///
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/// **Why is this bad?** Readability.
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///
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/// **Known problems:** False negatives. We currently only warn on some known types.
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///
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/// **Example:** `for x in y.iter() { .. }` (where y is a `Vec` or slice)
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declare_lint!{ pub EXPLICIT_ITER_LOOP, Warn,
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"for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do" }
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/// **What it does:** This lint checks for loops on `x.next()`. It is `Warn` by default.
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///
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/// **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).
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///
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/// **Known problems:** None
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///
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/// **Example:** `for x in y.next() { .. }`
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declare_lint!{ pub ITER_NEXT_LOOP, Warn,
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"for-looping over `_.next()` which is probably not intended" }
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/// **What it does:** This lint detects `loop + match` combinations that are easier written as a `while let` loop.
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///
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/// **Why is this bad?** The `while let` loop is usually shorter and more readable
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///
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/// **Known problems:** Sometimes the wrong binding is displayed (#383)
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///
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/// **Example:**
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///
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/// ```
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/// loop {
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/// let x = match y {
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/// Some(x) => x,
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/// None => break,
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/// }
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/// // .. do something with x
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/// }
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/// // is easier written as
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/// while let Some(x) = y {
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/// // .. do something with x
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/// }
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/// ```
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declare_lint!{ pub WHILE_LET_LOOP, Warn,
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"`loop { if let { ... } else break }` can be written as a `while let` loop" }
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/// **What it does:** This lint checks for using `collect()` on an iterator without using the result. It is `Warn` by default.
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///
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/// **Why is this bad?** It is more idiomatic to use a `for` loop over the iterator instead.
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///
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/// **Known problems:** None
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///
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/// **Example:** `vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();`
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declare_lint!{ pub UNUSED_COLLECT, Warn,
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"`collect()`ing an iterator without using the result; this is usually better \
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written as a for loop" }
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/// **What it does:** This lint 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(_)`.
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///
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/// **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.
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///
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/// **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.
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///
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/// **Examples**: `for x in 5..10-5 { .. }` (oops, stray `-`)
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declare_lint!{ pub REVERSE_RANGE_LOOP, Warn,
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"Iterating over an empty range, such as `10..0` or `5..5`" }
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/// **What it does:** This lint checks `for` loops over slices with an explicit counter and suggests the use of `.enumerate()`. It is `Warn` by default.
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///
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/// **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.
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///
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/// **Known problems:** None.
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///
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/// **Example:** `for i in 0..v.len() { foo(v[i]); }` or `for i in 0..v.len() { bar(i, v[i]); }`
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declare_lint!{ pub EXPLICIT_COUNTER_LOOP, Warn,
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"for-looping with an explicit counter when `_.enumerate()` would do" }
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/// **What it does:** This lint checks for empty `loop` expressions. It is `Warn` by default.
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///
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/// **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.
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///
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/// **Known problems:** None
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///
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/// **Example:** `loop {}`
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declare_lint!{ pub EMPTY_LOOP, Warn, "empty `loop {}` detected" }
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declare_lint!{ pub WHILE_LET_ON_ITERATOR, Warn, "using a while-let loop instead of a for loop on an iterator" }
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#[derive(Copy, Clone)]
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pub struct LoopsPass;
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impl LintPass for LoopsPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_RANGE_LOOP, EXPLICIT_ITER_LOOP, ITER_NEXT_LOOP,
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WHILE_LET_LOOP, UNUSED_COLLECT, REVERSE_RANGE_LOOP,
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EXPLICIT_COUNTER_LOOP, EMPTY_LOOP,
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WHILE_LET_ON_ITERATOR)
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}
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}
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impl LateLintPass for LoopsPass {
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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if let Some((pat, arg, body)) = recover_for_loop(expr) {
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check_for_loop(cx, pat, arg, body, expr);
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}
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// check for `loop { if let {} else break }` that could be `while let`
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// (also matches an explicit "match" instead of "if let")
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// (even if the "match" or "if let" is used for declaration)
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if let ExprLoop(ref block, _) = expr.node {
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// also check for empty `loop {}` statements
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if block.stmts.is_empty() && block.expr.is_none() {
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span_lint(cx, EMPTY_LOOP, expr.span,
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"empty `loop {}` detected. You may want to either \
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use `panic!()` or add `std::thread::sleep(..);` to \
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the loop body.");
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}
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// extract the expression from the first statement (if any) in a block
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let inner_stmt_expr = extract_expr_from_first_stmt(block);
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// extract the first expression (if any) from the block
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let inner_expr = extract_first_expr(block);
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let (extracted, collect_expr) = match inner_stmt_expr {
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Some(_) => (inner_stmt_expr, true), // check if an expression exists in the first statement
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None => (inner_expr, false), // if not, let's go for the first expression in the block
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};
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if let Some(inner) = extracted {
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if let ExprMatch(ref matchexpr, ref arms, ref source) = inner.node {
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// collect the remaining statements below the match
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let mut other_stuff = block.stmts
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.iter()
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.skip(1)
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.map(|stmt| {
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format!("{}", snippet(cx, stmt.span, ".."))
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}).collect::<Vec<String>>();
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if collect_expr { // if we have a statement which has a match,
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match block.expr { // then collect the expression (without semicolon) below it
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Some(ref expr) => other_stuff.push(format!("{}", snippet(cx, expr.span, ".."))),
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None => (),
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}
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}
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// ensure "if let" compatible match structure
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match *source {
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MatchSource::Normal | MatchSource::IfLetDesugar{..} => if
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arms.len() == 2 &&
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arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
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arms[1].pats.len() == 1 && arms[1].guard.is_none() &&
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// finally, check for "break" in the second clause
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is_break_expr(&arms[1].body)
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{
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if in_external_macro(cx, expr.span) { return; }
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let loop_body = match inner_stmt_expr {
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// FIXME: should probably be an ellipsis
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// tabbing and newline is probably a bad idea, especially for large blocks
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Some(_) => Cow::Owned(format!("{{\n {}\n}}", other_stuff.join("\n "))),
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None => expr_block(cx, &arms[0].body,
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Some(other_stuff.join("\n ")), ".."),
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};
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span_help_and_lint(cx, WHILE_LET_LOOP, expr.span,
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"this loop could be written as a `while let` loop",
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&format!("try\nwhile let {} = {} {}",
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snippet(cx, arms[0].pats[0].span, ".."),
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snippet(cx, matchexpr.span, ".."),
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loop_body));
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},
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_ => ()
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}
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}
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}
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}
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if let ExprMatch(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
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let pat = &arms[0].pats[0].node;
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if let (&PatEnum(ref path, Some(ref pat_args)),
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&ExprMethodCall(method_name, _, ref method_args)) =
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(pat, &match_expr.node) {
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let iter_expr = &method_args[0];
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if let Some(lhs_constructor) = path.segments.last() {
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if method_name.node.as_str() == "next" &&
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match_trait_method(cx, match_expr, &["core", "iter", "Iterator"]) &&
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lhs_constructor.identifier.name.as_str() == "Some" &&
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!is_iterator_used_after_while_let(cx, iter_expr) {
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let iterator = snippet(cx, method_args[0].span, "_");
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let loop_var = snippet(cx, pat_args[0].span, "_");
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span_help_and_lint(cx, WHILE_LET_ON_ITERATOR, expr.span,
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"this loop could be written as a `for` loop",
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&format!("try\nfor {} in {} {{...}}",
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loop_var,
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iterator));
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}
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}
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}
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}
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}
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fn check_stmt(&mut self, cx: &LateContext, stmt: &Stmt) {
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if let StmtSemi(ref expr, _) = stmt.node {
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if let ExprMethodCall(ref method, _, ref args) = expr.node {
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if args.len() == 1 && method.node.as_str() == "collect" &&
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match_trait_method(cx, expr, &["core", "iter", "Iterator"]) {
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span_lint(cx, UNUSED_COLLECT, expr.span, &format!(
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"you are collect()ing an iterator and throwing away the result. \
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Consider using an explicit for loop to exhaust the iterator"));
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}
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}
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}
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}
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}
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fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
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// check for looping over a range and then indexing a sequence with it
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// -> the iteratee must be a range literal
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if let ExprRange(Some(ref l), _) = arg.node {
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// Range should start with `0`
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if let ExprLit(ref lit) = l.node {
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if let LitInt(0, _) = lit.node {
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// the var must be a single name
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if let PatIdent(_, ref ident, _) = pat.node {
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let mut visitor = VarVisitor { cx: cx, var: ident.node.name,
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indexed: HashSet::new(), nonindex: false };
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walk_expr(&mut visitor, body);
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// linting condition: we only indexed one variable
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if visitor.indexed.len() == 1 {
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let indexed = visitor.indexed.into_iter().next().expect(
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"Len was nonzero, but no contents found");
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if visitor.nonindex {
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span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
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"the loop variable `{}` is used to index `{}`. Consider using \
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`for ({}, item) in {}.iter().enumerate()` or similar iterators",
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ident.node.name, indexed, ident.node.name, indexed));
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} else {
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span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
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"the loop variable `{}` is only used to index `{}`. \
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Consider using `for item in &{}` or similar iterators",
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ident.node.name, indexed, indexed));
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}
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}
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}
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}
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}
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}
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// if this for loop is iterating over a two-sided range...
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if let ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
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// ...and both sides are compile-time constant integers...
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if let Some(start_idx @ Constant::ConstantInt(..)) = constant_simple(start_expr) {
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if let Some(stop_idx @ Constant::ConstantInt(..)) = constant_simple(stop_expr) {
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// ...and the start index is greater than the stop index,
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// this loop will never run. This is often confusing for developers
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// who think that this will iterate from the larger value to the
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// smaller value.
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if start_idx > stop_idx {
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span_help_and_lint(cx, REVERSE_RANGE_LOOP, expr.span,
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"this range is empty so this for loop will never run",
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&format!("Consider using `({}..{}).rev()` if you are attempting to \
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iterate over this range in reverse", stop_idx, start_idx));
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} else if start_idx == stop_idx {
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// if they are equal, it's also problematic - this loop
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// will never run.
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span_lint(cx, REVERSE_RANGE_LOOP, expr.span,
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"this range is empty so this for loop will never run");
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}
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}
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}
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}
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if let ExprMethodCall(ref method, _, ref args) = arg.node {
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// just the receiver, no arguments
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if args.len() == 1 {
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let method_name = method.node;
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// check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
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if method_name.as_str() == "iter" || method_name.as_str() == "iter_mut" {
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if is_ref_iterable_type(cx, &args[0]) {
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let object = snippet(cx, args[0].span, "_");
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span_lint(cx, EXPLICIT_ITER_LOOP, expr.span, &format!(
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"it is more idiomatic to loop over `&{}{}` instead of `{}.{}()`",
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if method_name.as_str() == "iter_mut" { "mut " } else { "" },
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object, object, method_name));
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}
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}
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// check for looping over Iterator::next() which is not what you want
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else if method_name.as_str() == "next" &&
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match_trait_method(cx, arg, &["core", "iter", "Iterator"]) {
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span_lint(cx, ITER_NEXT_LOOP, expr.span,
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"you are iterating over `Iterator::next()` which is an Option; \
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this will compile but is probably not what you want");
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}
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}
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}
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// Look for variables that are incremented once per loop iteration.
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let mut visitor = IncrementVisitor { cx: cx, states: HashMap::new(), depth: 0, done: false };
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walk_expr(&mut visitor, body);
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// For each candidate, check the parent block to see if
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// it's initialized to zero at the start of the loop.
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let map = &cx.tcx.map;
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let parent_scope = map.get_enclosing_scope(expr.id).and_then(|id| map.get_enclosing_scope(id) );
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if let Some(parent_id) = parent_scope {
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if let NodeBlock(block) = map.get(parent_id) {
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for (id, _) in visitor.states.iter().filter( |&(_,v)| *v == VarState::IncrOnce) {
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let mut visitor2 = InitializeVisitor { cx: cx, end_expr: expr, var_id: id.clone(),
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state: VarState::IncrOnce, name: None,
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depth: 0,
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past_loop: false };
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walk_block(&mut visitor2, block);
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if visitor2.state == VarState::Warn {
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if let Some(name) = visitor2.name {
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span_lint(cx, EXPLICIT_COUNTER_LOOP, expr.span,
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&format!("the variable `{0}` is used as a loop counter. Consider \
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using `for ({0}, item) in {1}.enumerate()` \
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or similar iterators",
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name, snippet(cx, arg.span, "_")));
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}
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}
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}
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}
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}
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}
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/// Recover the essential nodes of a desugared for loop:
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/// `for pat in arg { body }` becomes `(pat, arg, body)`.
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fn recover_for_loop(expr: &Expr) -> Option<(&Pat, &Expr, &Expr)> {
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if_let_chain! {
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[
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let ExprMatch(ref iterexpr, ref arms, _) = expr.node,
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let ExprCall(_, ref iterargs) = iterexpr.node,
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iterargs.len() == 1 && arms.len() == 1 && arms[0].guard.is_none(),
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let ExprLoop(ref block, _) = arms[0].body.node,
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block.stmts.is_empty(),
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let Some(ref loopexpr) = block.expr,
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let ExprMatch(_, ref innerarms, MatchSource::ForLoopDesugar) = loopexpr.node,
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innerarms.len() == 2 && innerarms[0].pats.len() == 1,
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let PatEnum(_, Some(ref somepats)) = innerarms[0].pats[0].node,
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somepats.len() == 1
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], {
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return Some((&somepats[0],
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&iterargs[0],
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&innerarms[0].body));
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}
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}
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None
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}
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struct VarVisitor<'v, 't: 'v> {
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cx: &'v LateContext<'v, 't>, // context reference
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var: Name, // var name to look for as index
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indexed: HashSet<Name>, // indexed variables
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nonindex: bool, // has the var been used otherwise?
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}
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impl<'v, 't> Visitor<'v> for VarVisitor<'v, 't> {
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fn visit_expr(&mut self, expr: &'v Expr) {
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if let ExprPath(None, ref path) = expr.node {
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if path.segments.len() == 1 && path.segments[0].identifier.name == self.var {
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// we are referencing our variable! now check if it's as an index
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if_let_chain! {
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[
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let Some(parexpr) = get_parent_expr(self.cx, expr),
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let ExprIndex(ref seqexpr, _) = parexpr.node,
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let ExprPath(None, ref seqvar) = seqexpr.node,
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seqvar.segments.len() == 1
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], {
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self.indexed.insert(seqvar.segments[0].identifier.name);
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return; // no need to walk further
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}
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}
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// we are not indexing anything, record that
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self.nonindex = true;
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return;
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}
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}
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walk_expr(self, expr);
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}
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}
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fn is_iterator_used_after_while_let(cx: &LateContext, iter_expr: &Expr) -> bool {
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let def_id = match var_def_id(cx, iter_expr) {
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Some(id) => id,
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None => return false
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};
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let mut visitor = VarUsedAfterLoopVisitor {
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|
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.
|
|
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, &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 {
|
|
// 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) => Some(expr),
|
|
None if !block.stmts.is_empty() => match block.stmts[0].node {
|
|
StmtExpr(ref expr, _) | StmtSemi(ref expr, _) => Some(expr),
|
|
_ => 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,
|
|
// there won't be a `let <pat> = break` and so we can safely ignore the StmtDecl case
|
|
ExprBlock(ref b) => match extract_first_expr(b) {
|
|
Some(ref 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,
|
|
_ => ()
|
|
}
|
|
}
|
|
}
|
|
// Give up if there are nested loops
|
|
else if is_loop(expr) {
|
|
self.states.clear();
|
|
self.done = true;
|
|
return;
|
|
}
|
|
// Keep track of whether we're inside a conditional expression
|
|
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 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 {
|
|
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;
|
|
}
|
|
}
|
|
// If there are other loops between the declaration and the target loop, give up
|
|
else if !self.past_loop && is_loop(expr) {
|
|
self.state = VarState::DontWarn;
|
|
return;
|
|
}
|
|
// Keep track of whether we're inside a conditional expression
|
|
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
|
|
}
|
|
}
|