2015-12-04 10:12:53 +00:00
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use rustc::lint::*;
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use rustc_front::hir::*;
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use rustc_front::intravisit as visit;
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use rustc::front::map::Node;
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use rustc::middle::ty;
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use rustc::middle::ty::adjustment::AutoAdjustment;
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use rustc::middle::expr_use_visitor::*;
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use rustc::middle::infer;
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use rustc::middle::mem_categorization::{cmt, Categorization};
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use rustc::util::nodemap::NodeSet;
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use syntax::ast::NodeId;
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use syntax::codemap::Span;
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use utils::span_lint;
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pub struct EscapePass;
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2015-12-13 03:38:58 +00:00
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/// **What it does:** This lint checks for usage of `Box<T>` where an unboxed `T` would work fine
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///
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/// **Why is this bad?** This is an unnecessary allocation, and bad for performance
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///
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/// It is only necessary to allocate if you wish to move the box into something.
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///
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/// **Example:**
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///
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/// ```rust
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/// fn main() {
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/// let x = Box::new(1);
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/// foo(*x);
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/// println!("{}", *x);
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/// }
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2015-12-04 10:12:53 +00:00
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declare_lint!(pub BOXED_LOCAL, Warn, "using Box<T> where unnecessary");
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struct EscapeDelegate<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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set: NodeSet,
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}
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impl LintPass for EscapePass {
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fn get_lints(&self) -> LintArray {
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lint_array!(BOXED_LOCAL)
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}
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}
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impl LateLintPass for EscapePass {
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fn check_fn(&mut self,
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cx: &LateContext,
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_: visit::FnKind,
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decl: &FnDecl,
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body: &Block,
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_: Span,
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id: NodeId) {
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let param_env = ty::ParameterEnvironment::for_item(cx.tcx, id);
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let infcx = infer::new_infer_ctxt(cx.tcx, &cx.tcx.tables, Some(param_env), false);
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let mut v = EscapeDelegate {
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cx: cx,
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set: NodeSet(),
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};
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{
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let mut vis = ExprUseVisitor::new(&mut v, &infcx);
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vis.walk_fn(decl, body);
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}
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for node in v.set {
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span_lint(cx,
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BOXED_LOCAL,
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cx.tcx.map.span(node),
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"local variable doesn't need to be boxed here");
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}
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}
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}
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impl<'a, 'tcx: 'a> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
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fn consume(&mut self,
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_: NodeId,
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_: Span,
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cmt: cmt<'tcx>,
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mode: ConsumeMode) {
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if let Categorization::Local(lid) = cmt.cat {
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if self.set.contains(&lid) {
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if let Move(DirectRefMove) = mode {
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// moved out or in. clearly can't be localized
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self.set.remove(&lid);
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}
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}
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}
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}
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fn matched_pat(&mut self, _: &Pat, _: cmt<'tcx>, _: MatchMode) {}
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fn consume_pat(&mut self, consume_pat: &Pat, cmt: cmt<'tcx>, _: ConsumeMode) {
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if let Categorization::Rvalue(..) = cmt.cat {
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if let Some(Node::NodeStmt(st)) = self.cx
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.tcx
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.map
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.find(self.cx.tcx.map.get_parent_node(cmt.id)) {
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if let StmtDecl(ref decl, _) = st.node {
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if let DeclLocal(ref loc) = decl.node {
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if let Some(ref ex) = loc.init {
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if let ExprBox(..) = ex.node {
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if let ty::TyBox(..) = cmt.ty.sty {
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// let x = box (...)
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self.set.insert(consume_pat.id);
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}
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// TODO Box::new
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// TODO vec![]
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// TODO "foo".to_owned() and friends
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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 Categorization::Local(lid) = cmt.cat {
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if self.set.contains(&lid) {
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// let y = x where x is known
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// remove x, insert y
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self.set.insert(consume_pat.id);
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self.set.remove(&lid);
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}
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}
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}
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fn borrow(&mut self,
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borrow_id: NodeId,
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_: Span,
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cmt: cmt<'tcx>,
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_: ty::Region,
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_: ty::BorrowKind,
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loan_cause: LoanCause) {
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if let Categorization::Local(lid) = cmt.cat {
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if self.set.contains(&lid) {
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if let Some(&AutoAdjustment::AdjustDerefRef(adj)) = self.cx
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.tcx
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.tables
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.borrow()
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.adjustments
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.get(&borrow_id) {
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if LoanCause::AutoRef == loan_cause {
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// x.foo()
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if adj.autoderefs <= 0 {
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self.set.remove(&lid); // Used without autodereffing (i.e. x.clone())
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}
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} else {
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self.cx.sess().span_bug(cmt.span, "Unknown adjusted AutoRef");
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}
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} else if LoanCause::AddrOf == loan_cause {
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// &x
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if let Some(&AutoAdjustment::AdjustDerefRef(adj)) =
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self.cx.tcx.tables.borrow().adjustments
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.get(&self.cx.tcx.map.get_parent_node(borrow_id)) {
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if adj.autoderefs <= 1 {
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// foo(&x) where no extra autoreffing is happening
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self.set.remove(&lid);
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}
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}
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} else if LoanCause::MatchDiscriminant == loan_cause {
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self.set.remove(&lid); // `match x` can move
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}
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// do nothing for matches, etc. These can't escape
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}
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}
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}
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fn decl_without_init(&mut self, _: NodeId, _: Span) {}
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fn mutate(&mut self,
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_: NodeId,
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_: Span,
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_: cmt<'tcx>,
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_: MutateMode) {
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}
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}
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