use rustc::lint::*;
use rustc_front::hir::*;
use reexport::*;
-use rustc_front::visit::{Visitor, walk_expr};
+use rustc_front::intravisit::{Visitor, walk_expr, walk_block, walk_decl};
use rustc::middle::ty;
+use rustc::middle::def::DefLocal;
use consts::{constant_simple, Constant};
-use std::collections::HashSet;
+use rustc::front::map::Node::NodeBlock;
+use std::borrow::Cow;
+use std::collections::{HashSet, HashMap};
-use utils::{snippet, span_lint, get_parent_expr, match_trait_method, match_type,
- in_external_macro, expr_block, span_help_and_lint};
-use utils::{VEC_PATH, LL_PATH};
+use utils::{snippet, span_lint, get_parent_expr, match_trait_method, match_type, in_external_macro, expr_block,
+ span_help_and_lint, is_integer_literal, get_enclosing_block};
+use utils::{HASHMAP_PATH, VEC_PATH, LL_PATH};
+/// **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.
+///
+/// **Why is this bad?** Just iterating the collection itself makes the intent more clear and is probably faster.
+///
+/// **Known problems:** None
+///
+/// **Example:**
+/// ```
+/// 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:** This lint checks for loops on `x.iter()` where `&x` will do, and suggest the latter. It is `Warn` by default.
+///
+/// **Why is this bad?** Readability.
+///
+/// **Known problems:** False negatives. We currently only warn on some known types.
+///
+/// **Example:** `for x in y.iter() { .. }` (where y is a `Vec` or slice)
declare_lint!{ pub EXPLICIT_ITER_LOOP, Warn,
"for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do" }
+/// **What it does:** This lint checks for loops on `x.next()`. It is `Warn` by default.
+///
+/// **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:** `for x in y.next() { .. }`
declare_lint!{ pub ITER_NEXT_LOOP, Warn,
"for-looping over `_.next()` which is probably not intended" }
+/// **What it does:** This lint detects `loop + match` combinations that are easier written as a `while let` loop. It is `Warn` by default.
+///
+/// **Why is this bad?** The `while let` loop is usually shorter and more readable
+///
+/// **Known problems:** Sometimes the wrong binding is displayed (#383)
+///
+/// **Example:**
+///
+/// ```
+/// 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 }` can be written as a `while let` loop" }
+/// **What it does:** This lint checks for using `collect()` on an iterator without using the result. It is `Warn` by default.
+///
+/// **Why is this bad?** It is more idiomatic to use a `for` loop over the iterator instead.
+///
+/// **Known problems:** None
+///
+/// **Example:** `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:** 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(_)`. It is `Warn` by default.
+///
+/// **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.
+///
+/// **Examples**: `for x in 5..10-5 { .. }` (oops, stray `-`)
declare_lint!{ pub REVERSE_RANGE_LOOP, Warn,
"Iterating over an empty range, such as `10..0` or `5..5`" }
+/// **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.
+///
+/// **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:** `for i in 0..v.len() { foo(v[i]); }` or `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:** This lint checks for empty `loop` expressions. It is `Warn` by default.
+///
+/// **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:** `loop {}`
+declare_lint!{ pub EMPTY_LOOP, Warn, "empty `loop {}` detected" }
+
+/// **What it does:** This lint checks for `while let` expressions on iterators. It is `Warn` by default.
+///
+/// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys the intent better.
+///
+/// **Known problems:** None
+///
+/// **Example:** `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" }
+
#[derive(Copy, Clone)]
pub struct LoopsPass;
impl LintPass for LoopsPass {
fn get_lints(&self) -> LintArray {
- lint_array!(NEEDLESS_RANGE_LOOP, EXPLICIT_ITER_LOOP, ITER_NEXT_LOOP,
- WHILE_LET_LOOP, UNUSED_COLLECT, REVERSE_RANGE_LOOP)
+ 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)
}
+}
- fn check_expr(&mut self, cx: &Context, expr: &Expr) {
+impl LateLintPass for LoopsPass {
+ fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
if let Some((pat, arg, body)) = recover_for_loop(expr) {
- // check for looping over a range and then indexing a sequence with it
- // -> the iteratee must be a range literal
- if let ExprRange(Some(ref l), _) = arg.node {
- // Range should start with `0`
- if let ExprLit(ref lit) = l.node {
- if let LitInt(0, _) = lit.node {
-
- // the var must be a single name
- if let PatIdent(_, ref ident, _) = pat.node {
- let mut visitor = VarVisitor { cx: cx, var: ident.node.name,
- indexed: HashSet::new(), nonindex: false };
- walk_expr(&mut visitor, body);
- // linting condition: we only indexed one variable
- if visitor.indexed.len() == 1 {
- let indexed = visitor.indexed.into_iter().next().expect(
- "Len was nonzero, but no contents found");
- if visitor.nonindex {
- span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
- "the loop variable `{}` is used to index `{}`. Consider using \
- `for ({}, item) in {}.iter().enumerate()` or similar iterators",
- ident.node.name, indexed, ident.node.name, indexed));
- } else {
- span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
- "the loop variable `{}` is only used to index `{}`. \
- Consider using `for item in &{}` or similar iterators",
- ident.node.name, indexed, indexed));
+ 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 {
+ // collect the remaining statements below the match
+ let mut other_stuff = block.stmts
+ .iter()
+ .skip(1)
+ .map(|stmt| format!("{}", snippet(cx, stmt.span, "..")))
+ .collect::<Vec<String>>();
+ if inner_stmt_expr.is_some() {
+ // if we have a statement which has a match,
+ if let Some(ref expr) = block.expr {
+ // then collect the expression (without semicolon) below it
+ other_stuff.push(format!("{}", snippet(cx, expr.span, "..")));
+ }
+ }
+
+ // 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;
}
+ let loop_body = if inner_stmt_expr.is_some() {
+ // FIXME: should probably be an ellipsis
+ // tabbing and newline is probably a bad idea, especially for large blocks
+ Cow::Owned(format!("{{\n {}\n}}", other_stuff.join("\n ")))
+ } else {
+ expr_block(cx, &arms[0].body, Some(other_stuff.join("\n ")), "..")
+ };
+ span_help_and_lint(cx,
+ WHILE_LET_LOOP,
+ expr.span,
+ "this loop could be written as a `while let` loop",
+ &format!("try\nwhile let {} = {} {}",
+ snippet(cx, arms[0].pats[0].span, ".."),
+ snippet(cx, matchexpr.span, ".."),
+ loop_body));
}
}
+ _ => (),
}
}
}
-
- // if this for loop is iterating over a two-sided range...
- if let ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
- // ...and both sides are compile-time constant integers...
- if let Some(Constant::ConstantInt(start_idx, _)) = constant_simple(start_expr) {
- if let Some(Constant::ConstantInt(stop_idx, _)) = constant_simple(stop_expr) {
- // ...and the start index is greater than the stop index,
- // this loop will never run. This is often confusing for developers
- // who think that this will iterate from the larger value to the
- // smaller value.
- if start_idx > stop_idx {
- span_help_and_lint(cx, REVERSE_RANGE_LOOP, expr.span,
- "this range is empty so this for loop will never run",
- &format!("Consider using `({}..{}).rev()` if you are attempting to \
- iterate over this range in reverse", stop_idx, start_idx));
- } else if start_idx == stop_idx {
- // 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");
- }
+ }
+ if let ExprMatch(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
+ let pat = &arms[0].pats[0].node;
+ if let (&PatEnum(ref path, Some(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, &["core", "iter", "Iterator"]) &&
+ lhs_constructor.identifier.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_help_and_lint(cx,
+ WHILE_LET_ON_ITERATOR,
+ expr.span,
+ "this loop could be written as a `for` loop",
+ &format!("try\nfor {} in {} {{...}}", loop_var, iterator));
}
}
}
+ }
+ }
- if let ExprMethodCall(ref method, _, ref args) = arg.node {
- // just the receiver, no arguments
- if args.len() == 1 {
- let method_name = method.node.name;
- // 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]) {
- let object = snippet(cx, args[0].span, "_");
- span_lint(cx, EXPLICIT_ITER_LOOP, expr.span, &format!(
- "it is more idiomatic to loop over `&{}{}` instead of `{}.{}()`",
- if method_name == "iter_mut" { "mut " } else { "" },
- object, object, method_name));
- }
+ 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, &["core", "iter", "Iterator"]) {
+ span_lint(cx,
+ UNUSED_COLLECT,
+ expr.span,
+ &format!("you are collect()ing an iterator and throwing away the result. Consider \
+ using an explicit for loop to exhaust the iterator"));
+ }
+ }
+ }
+ }
+}
+
+fn 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_explicit_iter(cx, arg, expr);
+ check_for_loop_explicit_counter(cx, 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 ExprRange(Some(ref l), ref r) = arg.node {
+ // the var must be a single name
+ if let PatIdent(_, ref ident, _) = pat.node {
+ let mut visitor = VarVisitor {
+ cx: cx,
+ var: ident.node.name,
+ indexed: HashSet::new(),
+ nonindex: false,
+ };
+ walk_expr(&mut visitor, body);
+ // linting condition: we only indexed one variable
+ if visitor.indexed.len() == 1 {
+ let indexed = visitor.indexed
+ .into_iter()
+ .next()
+ .expect("Len was nonzero, but no contents found");
+
+ let starts_at_zero = is_integer_literal(l, 0);
+
+ let skip: Cow<_> = if starts_at_zero {
+ "".into()
+ }
+ else {
+ format!(".skip({})", snippet(cx, l.span, "..")).into()
+ };
+
+ let take: Cow<_> = if let Some(ref r) = *r {
+ if !is_len_call(&r, &indexed) {
+ format!(".take({})", snippet(cx, r.span, "..")).into()
}
- // check for looping over Iterator::next() which is not what you want
- else if method_name == "next" &&
- match_trait_method(cx, arg, &["core", "iter", "Iterator"]) {
- span_lint(cx, ITER_NEXT_LOOP, expr.span,
- "you are iterating over `Iterator::next()` which is an Option; \
- this will compile but is probably not what you want");
+ else {
+ "".into()
}
+ } else {
+ "".into()
+ };
+
+ if visitor.nonindex {
+ span_lint(cx,
+ NEEDLESS_RANGE_LOOP,
+ expr.span,
+ &format!("the loop variable `{}` is used to index `{}`. \
+ Consider using `for ({}, item) in {}.iter().enumerate(){}{}` or similar iterators",
+ ident.node.name,
+ indexed,
+ ident.node.name,
+ indexed,
+ take,
+ skip));
+ } else {
+ let repl = if starts_at_zero && take.is_empty() {
+ format!("&{}", indexed)
+ }
+ else {
+ format!("{}.iter(){}{}", indexed, take, skip)
+ };
+
+ span_lint(cx,
+ NEEDLESS_RANGE_LOOP,
+ expr.span,
+ &format!("the loop variable `{}` is only used to index `{}`. \
+ Consider using `for item in {}` or similar iterators",
+ ident.node.name,
+ indexed,
+ repl));
}
}
}
- // check for `loop { if let {} else break }` that could be `while let`
- // (also matches explicit "match" instead of "if let")
- if let ExprLoop(ref block, _) = expr.node {
- // extract a single expression
- if let Some(inner) = extract_single_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() &&
- // finally, check for "break" in the second clause
- is_break_expr(&arms[1].body)
- {
- if in_external_macro(cx, expr.span) { return; }
- span_help_and_lint(cx, WHILE_LET_LOOP, expr.span,
- "this loop could be written as a `while let` loop",
- &format!("try\nwhile let {} = {} {}",
- snippet(cx, arms[0].pats[0].span, ".."),
- snippet(cx, matchexpr.span, ".."),
- expr_block(cx, &arms[0].body, "..")));
- },
- _ => ()
- }
+ }
+}
+
+fn 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].identifier.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 ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
+ // ...and both sides are compile-time constant integers...
+ if let Some(start_idx @ Constant::ConstantInt(..)) = constant_simple(start_expr) {
+ if let Some(stop_idx @ Constant::ConstantInt(..)) = constant_simple(stop_expr) {
+ // ...and the start index is greater than the stop index,
+ // this loop will never run. This is often confusing for developers
+ // who think that this will iterate from the larger value to the
+ // smaller value.
+ if start_idx > stop_idx {
+ span_help_and_lint(cx,
+ REVERSE_RANGE_LOOP,
+ expr.span,
+ "this range is empty so this for loop will never run",
+ &format!("Consider using `({}..{}).rev()` if you are attempting to iterate \
+ over this range in reverse",
+ stop_idx,
+ start_idx));
+ } else if start_idx == stop_idx {
+ // 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_stmt(&mut self, cx: &Context, stmt: &Stmt) {
- if let StmtSemi(ref expr, _) = stmt.node {
- if let ExprMethodCall(ref method, _, ref args) = expr.node {
- if args.len() == 1 && method.node.name == "collect" &&
- match_trait_method(cx, expr, &["core", "iter", "Iterator"]) {
- span_lint(cx, UNUSED_COLLECT, expr.span, &format!(
- "you are collect()ing an iterator and throwing away the result. \
- Consider using an explicit for loop to exhaust the iterator"));
+fn check_for_loop_explicit_iter(cx: &LateContext, arg: &Expr, expr: &Expr) {
+ 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, &["core", "iter", "Iterator"]) {
+ span_lint(cx,
+ ITER_NEXT_LOOP,
+ expr.span,
+ "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
+ probably not what you want");
+ }
+ }
+ }
+
+}
+
+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.clone(),
+ 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, "_")));
+ }
}
}
}
}
struct VarVisitor<'v, 't: 'v> {
- cx: &'v Context<'v, 't>, // context reference
- var: Name, // var name to look for as index
- indexed: HashSet<Name>, // indexed variables
- nonindex: bool, // has the var been used otherwise?
+ cx: &'v LateContext<'v, 't>, // context reference
+ var: Name, // var name to look for as index
+ indexed: HashSet<Name>, // indexed variables
+ nonindex: bool, // has the var been used otherwise?
}
impl<'v, 't> Visitor<'v> for VarVisitor<'v, 't> {
}
}
+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.
-fn is_ref_iterable_type(cx: &Context, e: &Expr) -> bool {
+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"])
+ is_iterable_array(ty) || match_type(cx, ty, &VEC_PATH) || match_type(cx, ty, &LL_PATH) ||
+ match_type(cx, ty, &HASHMAP_PATH) || 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
+ // IntoIterator is currently only implemented for array sizes <= 32 in rustc
match ty.sty {
ty::TyArray(_, 0...32) => true,
- _ => false
+ _ => false,
}
}
-/// If block consists of a single expression (with or without semicolon), return it.
-fn extract_single_expr(block: &Block) -> Option<&Expr> {
- match (&block.stmts.len(), &block.expr) {
- (&1, &None) => match block.stmts[0].node {
- StmtExpr(ref expr, _) |
- StmtSemi(ref expr, _) => Some(expr),
- _ => None,
- },
- (&0, &Some(ref expr)) => Some(expr),
- _ => None
+/// 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,
}
}
fn is_break_expr(expr: &Expr) -> bool {
match expr.node {
ExprBreak(None) => true,
- ExprBlock(ref b) => match extract_single_expr(b) {
- Some(ref subexpr) => is_break_expr(subexpr),
- None => false,
- },
+ // 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,
+ _ => (),
+ }
+ }
+ } 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 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;
+ }
+ } 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 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,
}
}
projects / rust.git / blobdiff