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Track what drop obligations are established on match arms.

Browse source 
This is accomplished by:

1. Add `MatchMode` enum to `expr_use_visitor`.

2. Computing the match mode for each pattern via a pre-pass, and then
   passing the mode along when visiting the pattern in
   expr_use_visitor.

3. Adding a `fn matched_pat` callback to expr_use_visitor, which is
   called on interior struct and enum nodes of the pattern (as opposed
   to `fn consume_pat`, which is only invoked for identifiers at the
   leaves of the pattern), and invoking it accordingly.

Of particular interest are the `cat_downcast` instances established
when matching enum variants.
This commit is contained in:
Felix S. Klock II 2014-09-16 15:24:56 +02:00
parent 6f7cb8c618
commit 09d67fd777
7 changed files with 278 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
src/librustc/middle/borrowck/check_loans.rs
View file

@ -103,6 +103,11 @@ impl<'a, 'tcx> euv::Delegate<'tcx> for CheckLoanCtxt<'a, 'tcx> {
self.consume_common(consume_id, consume_span, cmt, mode);
}
fn matched_pat(&mut self,
_matched_pat: &ast::Pat,
_cmt: mc::cmt,
_mode: euv::MatchMode) { }
fn consume_pat(&mut self,
consume_pat: &ast::Pat,
cmt: mc::cmt<'tcx>,

10
src/librustc/middle/borrowck/gather_loans/mod.rs
View file

@ -88,6 +88,16 @@ impl<'a, 'tcx> euv::Delegate<'tcx> for GatherLoanCtxt<'a, 'tcx> {
}
}
fn matched_pat(&mut self,
matched_pat: &ast::Pat,
cmt: mc::cmt<'tcx>,
mode: euv::MatchMode) {
debug!("matched_pat(matched_pat={}, cmt={}, mode={})",
matched_pat.repr(self.tcx()),
cmt.repr(self.tcx()),
mode);
}
fn consume_pat(&mut self,
consume_pat: &ast::Pat,
cmt: mc::cmt<'tcx>,

2
src/librustc/middle/check_match.rs
View file

@ -18,6 +18,7 @@ use middle::def::*;
use middle::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Init};
use middle::expr_use_visitor::{JustWrite, LoanCause, MutateMode};
use middle::expr_use_visitor::{WriteAndRead};
use middle::expr_use_visitor as euv;
use middle::mem_categorization::cmt;
use middle::pat_util::*;
use middle::ty::*;
@ -1024,6 +1025,7 @@ struct MutationChecker<'a, 'tcx: 'a> {
}
impl<'a, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'tcx> {
fn matched_pat(&mut self, _: &Pat, _: cmt, _: euv::MatchMode) {}
fn consume(&mut self, _: NodeId, _: Span, _: cmt, _: ConsumeMode) {}
fn consume_pat(&mut self, _: &Pat, _: cmt, _: ConsumeMode) {}
fn borrow(&mut self,

5
src/librustc/middle/check_rvalues.rs
View file

@ -59,6 +59,11 @@ impl<'a, 'tcx> euv::Delegate<'tcx> for RvalueContext<'a, 'tcx> {
}
}
fn matched_pat(&mut self,
_matched_pat: &ast::Pat,
_cmt: mc::cmt,
_mode: euv::MatchMode) {}
fn consume_pat(&mut self,
_consume_pat: &ast::Pat,
_cmt: mc::cmt,

6
src/librustc/middle/check_static.rs
View file

@ -325,6 +325,12 @@ impl<'tcx> euv::Delegate<'tcx> for GlobalChecker {
_assignment_span: Span,
_assignee_cmt: mc::cmt,
_mode: euv::MutateMode) {}
fn matched_pat(&mut self,
_: &ast::Pat,
_: mc::cmt,
_: euv::MatchMode) {}
fn consume_pat(&mut self,
_consume_pat: &ast::Pat,
_cmt: mc::cmt,

259
src/librustc/middle/expr_use_visitor.rs
View file

@ -18,6 +18,8 @@ pub use self::MutateMode::*;
pub use self::LoanCause::*;
pub use self::ConsumeMode::*;
pub use self::MoveReason::*;
pub use self::MatchMode::*;
use self::TrackMatchMode::*;
use self::OverloadedCallType::*;
use middle::{def, region, pat_util};
@ -48,6 +50,23 @@ pub trait Delegate<'tcx> {
cmt: mc::cmt<'tcx>,
mode: ConsumeMode);
// The value found at `cmt` has been determined to match the
// pattern binding `matched_pat`, and its subparts are being
// copied or moved depending on `mode`. Note that `matched_pat`
// is called on all variant/structs in the pattern (i.e., the
// interior nodes of the pattern's tree structure) while
// consume_pat is called on the binding identifiers in the pattern
// (which are leaves of the pattern's tree structure).
//
// Note that variants/structs and identifiers are disjoint; thus
// `matched_pat` and `consume_pat` are never both called on the
// same input pattern structure (though of `consume_pat` can be
// called on a subpart of an input passed to `matched_pat).
fn matched_pat(&mut self,
matched_pat: &ast::Pat,
cmt: mc::cmt<'tcx>,
mode: MatchMode);
// The value found at `cmt` is either copied or moved via the
// pattern binding `consume_pat`, depending on mode.
fn consume_pat(&mut self,
@ -103,6 +122,79 @@ pub enum MoveReason {
CaptureMove,
}
#[deriving(PartialEq,Show)]
pub enum MatchMode {
NonBindingMatch,
BorrowingMatch,
CopyingMatch,
MovingMatch,
}
#[deriving(PartialEq,Show)]
enum TrackMatchMode<T> {
Unknown, Definite(MatchMode), Conflicting,
}
impl<T> TrackMatchMode<T> {
// Builds up the whole match mode for a pattern from its constituent
// parts. The lattice looks like this:
//
// Conflicting
// / \
// / \
// Borrowing Moving
// \ /
// \ /
// Copying
// |
// NonBinding
// |
// Unknown
//
// examples:
//
// * `(_, some_int)` pattern is Copying, since
// NonBinding + Copying => Copying
//
// * `(some_int, some_box)` pattern is Moving, since
// Copying + Moving => Moving
//
// * `(ref x, some_box)` pattern is Conflicting, since
// Borrowing + Moving => Conflicting
//
// Note that the `Unknown` and `Conflicting` states are
// represented separately from the other more interesting
// `Definite` states, which simplifies logic here somewhat.
fn lub(&mut self, mode: MatchMode) {
*self = match (*self, mode) {
// Note that clause order below is very significant.
(Unknown, new) => Definite(new),
(Definite(old), new) if old == new => Definite(old),
(Definite(old), NonBindingMatch) => Definite(old),
(Definite(NonBindingMatch), new) => Definite(new),
(Definite(old), CopyingMatch) => Definite(old),
(Definite(CopyingMatch), new) => Definite(new),
(Definite(_), _) => Conflicting,
(Conflicting, _) => *self,
};
}
fn match_mode(&self) -> MatchMode {
match *self {
Unknown => NonBindingMatch,
Definite(mode) => mode,
Conflicting => {
// Conservatively return MovingMatch to let the
// compiler continue to make progress.
MovingMatch
}
}
}
}
#[deriving(PartialEq,Show)]
pub enum MutateMode {
Init,
@ -251,7 +343,7 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
ty::ReScope(fn_body_scope), // Args live only as long as the fn body.
arg_ty);
self.walk_pat(arg_cmt, &*arg.pat);
self.walk_irrefutable_pat(arg_cmt, &*arg.pat);
}
}
@ -390,7 +482,9 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
// treatment of the discriminant is handled while walking the arms.
for arm in arms.iter() {
self.walk_arm(discr_cmt.clone(), arm);
let mode = self.arm_move_mode(discr_cmt.clone(), arm);
let mode = mode.match_mode();
self.walk_arm(discr_cmt.clone(), arm, mode);
}
}
@ -448,7 +542,7 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
pat.span,
ty::ReScope(blk_scope),
pattern_type);
self.walk_pat(pat_cmt, &**pat);
self.walk_irrefutable_pat(pat_cmt, &**pat);
self.walk_block(&**blk);
}
@ -617,7 +711,7 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
// `walk_pat`:
self.walk_expr(&**expr);
let init_cmt = return_if_err!(self.mc.cat_expr(&**expr));
self.walk_pat(init_cmt, &*local.pat);
self.walk_irrefutable_pat(init_cmt, &*local.pat);
}
}
}
@ -824,9 +918,17 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
return true;
}
fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &ast::Arm) {
fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &ast::Arm) -> TrackMatchMode<Span> {
let mut mode = Unknown;
for pat in arm.pats.iter() {
self.walk_pat(discr_cmt.clone(), &**pat);
self.determine_pat_move_mode(discr_cmt.clone(), &**pat, &mut mode);
}
mode
}
fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &ast::Arm, mode: MatchMode) {
for pat in arm.pats.iter() {
self.walk_pat(discr_cmt.clone(), &**pat, mode);
}
for guard in arm.guard.iter() {
@ -836,21 +938,71 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
self.consume_expr(&*arm.body);
}
fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &ast::Pat) {
/// Walks an pat that occurs in isolation (i.e. top-level of fn
/// arg or let binding. *Not* a match arm or nested pat.)
fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &ast::Pat) {
let mut mode = Unknown;
self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
let mode = mode.match_mode();
self.walk_pat(cmt_discr, pat, mode);
}
/// Identifies any bindings within `pat` and accumulates within
/// `mode` whether the overall pattern/match structure is a move,
/// copy, or borrow.
fn determine_pat_move_mode(&mut self,
cmt_discr: mc::cmt<'tcx>,
pat: &ast::Pat,
mode: &mut TrackMatchMode<Span>) {
debug!("determine_pat_move_mode cmt_discr={} pat={}", cmt_discr.repr(self.tcx()),
pat.repr(self.tcx()));
return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
let tcx = self.typer.tcx();
let def_map = &self.typer.tcx().def_map;
if pat_util::pat_is_binding(def_map, pat) {
match pat.node {
ast::PatIdent(ast::BindByRef(_), _, _) =>
mode.lub(BorrowingMatch),
ast::PatIdent(ast::BindByValue(_), _, _) => {
match copy_or_move(tcx, cmt_pat.ty, PatBindingMove) {
Copy => mode.lub(CopyingMatch),
Move(_) => mode.lub(MovingMatch),
}
}
_ => {
tcx.sess.span_bug(
pat.span,
"binding pattern not an identifier");
}
}
}
}));
}
/// The core driver for walking a pattern; `match_mode` must be
/// established up front, e.g. via `determine_pat_move_mode` (see
/// also `walk_irrefutable_pat` for patterns that stand alone).
fn walk_pat(&mut self,
cmt_discr: mc::cmt<'tcx>,
pat: &ast::Pat,
match_mode: MatchMode) {
debug!("walk_pat cmt_discr={} pat={}", cmt_discr.repr(self.tcx()),
pat.repr(self.tcx()));
let mc = &self.mc;
let typer = self.typer;
let tcx = typer.tcx();
let def_map = &self.typer.tcx().def_map;
let delegate = &mut self.delegate;
return_if_err!(mc.cat_pattern(cmt_discr, &*pat, |mc, cmt_pat, pat| {
return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
if pat_util::pat_is_binding(def_map, pat) {
let tcx = typer.tcx();
debug!("binding cmt_pat={} pat={}",
debug!("binding cmt_pat={} pat={} match_mode={}",
cmt_pat.repr(tcx),
pat.repr(tcx));
pat.repr(tcx),
match_mode);
// pat_ty: the type of the binding being produced.
let pat_ty = return_if_err!(typer.node_ty(pat.id));
@ -933,6 +1085,93 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
}
}
}));
// Do a second pass over the pattern, calling `matched_pat` on
// the interior nodes (enum variants and structs), as opposed
// to the above loop's visit of than the bindings that form
// the leaves of the pattern tree structure.
return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
let def_map = def_map.borrow();
let tcx = typer.tcx();
match pat.node {
ast::PatEnum(_, _) | ast::PatIdent(_, _, None) | ast::PatStruct(..) => {
match def_map.get(&pat.id) {
None => {
// no definition found: pat is not a
// struct or enum pattern.
}
Some(&def::DefVariant(enum_did, variant_did, _is_struct)) => {
let downcast_cmt =
if ty::enum_is_univariant(tcx, enum_did) {
cmt_pat
} else {
let cmt_pat_ty = cmt_pat.ty;
mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
};
debug!("variant downcast_cmt={} pat={}",
downcast_cmt.repr(tcx),
pat.repr(tcx));
delegate.matched_pat(pat, downcast_cmt, match_mode);
}
Some(&def::DefStruct(..)) | Some(&def::DefTy(_, false)) => {
// A struct (in either the value or type
// namespace; we encounter the former on
// e.g. patterns for unit structs).
debug!("struct cmt_pat={} pat={}",
cmt_pat.repr(tcx),
pat.repr(tcx));
delegate.matched_pat(pat, cmt_pat, match_mode);
}
Some(&def::DefConst(..)) |
Some(&def::DefLocal(..)) => {
// This is a leaf (i.e. identifier binding
// or constant value to match); thus no
// `matched_pat` call.
}
Some(def @ &def::DefTy(_, true)) => {
// An enum's type -- should never be in a
// pattern.
let msg = format!("Pattern has unexpected type: {}", def);
tcx.sess.span_bug(pat.span, msg.as_slice())
}
Some(def) => {
// Remaining cases are e.g. DefFn, to
// which identifiers within patterns
// should not resolve.
let msg = format!("Pattern has unexpected def: {}", def);
tcx.sess.span_bug(pat.span, msg.as_slice())
}
}
}
ast::PatIdent(_, _, Some(_)) => {
// Do nothing; this is a binding (not a enum
// variant or struct), and the cat_pattern call
// will visit the substructure recursively.
}
ast::PatWild(_) | ast::PatTup(..) | ast::PatBox(..) |
ast::PatRegion(..) | ast::PatLit(..) | ast::PatRange(..) |
ast::PatVec(..) | ast::PatMac(..) => {
// Similarly, each of these cases does not
// correspond to a enum variant or struct, so we
// do not do any `matched_pat` calls for these
// cases either.
}
}
}));
}
fn walk_captures(&mut self, closure_expr: &ast::Expr) {

1
src/librustc_trans/trans/_match.rs
View file

@ -1274,6 +1274,7 @@ struct ReassignmentChecker {
impl<'tcx> euv::Delegate<'tcx> for ReassignmentChecker {
fn consume(&mut self, _: ast::NodeId, _: Span, _: mc::cmt, _: euv::ConsumeMode) {}
fn matched_pat(&mut self, _: &ast::Pat, _: mc::cmt, _: euv::MatchMode) {}
fn consume_pat(&mut self, _: &ast::Pat, _: mc::cmt, _: euv::ConsumeMode) {}
fn borrow(&mut self, _: ast::NodeId, _: Span, _: mc::cmt, _: ty::Region,
_: ty::BorrowKind, _: euv::LoanCause) {}