rust/src/librustc/middle/kind.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use core::prelude::*;

use middle::freevars::freevar_entry;
use middle::freevars;
use middle::lint::{non_implicitly_copyable_typarams, implicit_copies};
use middle::liveness;
use middle::pat_util;
use middle::ty::{Kind, kind_copyable, kind_noncopyable, kind_const};
use middle::ty;
use middle::typeck;
use middle;
use util::ppaux::{ty_to_str, tys_to_str};

use core::option;
use core::str;
use core::vec;
use std::oldmap::HashMap;
use syntax::ast::*;
use syntax::codemap::{span, spanned};
use syntax::print::pprust::expr_to_str;
use syntax::{visit, ast_util};

// Kind analysis pass.
//
// There are several kinds defined by various operations. The most restrictive
// kind is noncopyable. The noncopyable kind can be extended with any number
// of the following attributes.
//
//  send: Things that can be sent on channels or included in spawned closures.
//  copy: Things that can be copied.
//  const: Things thare are deeply immutable. They are guaranteed never to
//    change, and can be safely shared without copying between tasks.
//  owned: Things that do not contain borrowed pointers.
//
// Send includes scalar types as well as classes and unique types containing
// only sendable types.
//
// Copy includes boxes, closure and unique types containing copyable types.
//
// Const include scalar types, things without non-const fields, and pointers
// to const things.
//
// This pass ensures that type parameters are only instantiated with types
// whose kinds are equal or less general than the way the type parameter was
// annotated (with the `send`, `copy` or `const` keyword).
//
// It also verifies that noncopyable kinds are not copied. Sendability is not
// applied, since none of our language primitives send. Instead, the sending
// primitives in the stdlib are explicitly annotated to only take sendable
// types.

pub const try_adding: &str = "Try adding a move";

pub fn kind_to_str(k: Kind) -> ~str {
    let mut kinds = ~[];

    if ty::kind_lteq(kind_const(), k) {
        kinds.push(~"const");
    }

    if ty::kind_can_be_copied(k) {
        kinds.push(~"copy");
    }

    if ty::kind_can_be_sent(k) {
        kinds.push(~"owned");
    } else if ty::kind_is_durable(k) {
        kinds.push(~"&static");
    }

    str::connect(kinds, ~" ")
}

pub type rval_map = HashMap<node_id, ()>;

pub type ctx = {
    tcx: ty::ctxt,
    method_map: typeck::method_map,
    last_use_map: liveness::last_use_map,
    current_item: node_id
};

pub fn check_crate(tcx: ty::ctxt,
                   method_map: typeck::method_map,
                   last_use_map: liveness::last_use_map,
                   crate: @crate) {
    let ctx = {tcx: tcx,
               method_map: method_map,
               last_use_map: last_use_map,
               current_item: -1};
    let visit = visit::mk_vt(@visit::Visitor {
        visit_arm: check_arm,
        visit_expr: check_expr,
        visit_fn: check_fn,
        visit_ty: check_ty,
        visit_item: fn@(i: @item, cx: ctx, v: visit::vt<ctx>) {
            visit::visit_item(i, {current_item: i.id,.. cx}, v);
        },
        .. *visit::default_visitor()
    });
    visit::visit_crate(*crate, ctx, visit);
    tcx.sess.abort_if_errors();
}

type check_fn = fn@(ctx, @freevar_entry);

// Yields the appropriate function to check the kind of closed over
// variables. `id` is the node_id for some expression that creates the
// closure.
fn with_appropriate_checker(cx: ctx, id: node_id, b: fn(check_fn)) {
    fn check_for_uniq(cx: ctx, fv: @freevar_entry) {
        // all captured data must be sendable, regardless of whether it is
        // moved in or copied in.  Note that send implies owned.
        let id = ast_util::def_id_of_def(fv.def).node;
        let var_t = ty::node_id_to_type(cx.tcx, id);
        if !check_send(cx, var_t, fv.span) { return; }

        // check that only immutable variables are implicitly copied in
        check_imm_free_var(cx, fv.def, fv.span);
    }

    fn check_for_box(cx: ctx, fv: @freevar_entry) {
        // all captured data must be owned
        let id = ast_util::def_id_of_def(fv.def).node;
        let var_t = ty::node_id_to_type(cx.tcx, id);
        if !check_durable(cx.tcx, var_t, fv.span) { return; }

        // check that only immutable variables are implicitly copied in
        check_imm_free_var(cx, fv.def, fv.span);
    }

    fn check_for_block(_cx: ctx, _fv: @freevar_entry) {
        // no restrictions
    }

    fn check_for_bare(cx: ctx, fv: @freevar_entry) {
        cx.tcx.sess.span_err(
            fv.span,
            ~"attempted dynamic environment capture");
    }

    let fty = ty::node_id_to_type(cx.tcx, id);
    match ty::get(fty).sty {
        ty::ty_closure(ty::ClosureTy {sigil: OwnedSigil, _}) => {
            b(check_for_uniq)
        }
        ty::ty_closure(ty::ClosureTy {sigil: ManagedSigil, _}) => {
            b(check_for_box)
        }
        ty::ty_closure(ty::ClosureTy {sigil: BorrowedSigil, _}) => {
            b(check_for_block)
        }
        ty::ty_bare_fn(_) => {
            b(check_for_bare)
        }
        ref s => {
            cx.tcx.sess.bug(
                fmt!("expect fn type in kind checker, not %?", s));
        }
    }
}

// Check that the free variables used in a shared/sendable closure conform
// to the copy/move kind bounds. Then recursively check the function body.
fn check_fn(fk: visit::fn_kind, decl: fn_decl, body: blk, sp: span,
            fn_id: node_id, cx: ctx, v: visit::vt<ctx>) {

    // Check kinds on free variables:
    do with_appropriate_checker(cx, fn_id) |chk| {
        for vec::each(*freevars::get_freevars(cx.tcx, fn_id)) |fv| {
            chk(cx, *fv);
        }
    }

    visit::visit_fn(fk, decl, body, sp, fn_id, cx, v);
}

fn check_arm(a: arm, cx: ctx, v: visit::vt<ctx>) {
    for vec::each(a.pats) |p| {
        do pat_util::pat_bindings(cx.tcx.def_map, *p) |mode, id, span, _pth| {
            if mode == bind_by_copy {
                let t = ty::node_id_to_type(cx.tcx, id);
                let reason = "consider binding with `ref` or `move` instead";
                check_copy(cx, t, span, reason);
            }
        }
    }
    visit::visit_arm(a, cx, v);
}

pub fn check_expr(e: @expr, cx: ctx, v: visit::vt<ctx>) {
    debug!("kind::check_expr(%s)", expr_to_str(e, cx.tcx.sess.intr()));

    // Handle any kind bounds on type parameters
    let type_parameter_id = match e.node {
        expr_index(*)|expr_assign_op(*)|
        expr_unary(*)|expr_binary(*)|expr_method_call(*) => e.callee_id,
        _ => e.id
    };
    do option::iter(&cx.tcx.node_type_substs.find(&type_parameter_id)) |ts| {
        let bounds = match e.node {
          expr_path(_) => {
            let did = ast_util::def_id_of_def(cx.tcx.def_map.get(&e.id));
            ty::lookup_item_type(cx.tcx, did).bounds
          }
          _ => {
            // Type substitutions should only occur on paths and
            // method calls, so this needs to be a method call.

            // Even though the callee_id may have been the id with
            // node_type_substs, e.id is correct here.
            ty::method_call_bounds(cx.tcx, cx.method_map, e.id).expect(
                ~"non path/method call expr has type substs??")
          }
        };
        if vec::len(*ts) != vec::len(*bounds) {
            // Fail earlier to make debugging easier
            die!(fmt!("internal error: in kind::check_expr, length \
                       mismatch between actual and declared bounds: actual = \
                        %s (%u tys), declared = %? (%u tys)",
                      tys_to_str(cx.tcx, *ts), ts.len(),
                      *bounds, (*bounds).len()));
        }
        for vec::each2(*ts, *bounds) |ty, bound| {
            check_bounds(cx, type_parameter_id, e.span, *ty, *bound)
        }
    }

    match e.node {
        expr_cast(source, _) => {
            check_cast_for_escaping_regions(cx, source, e);
            check_kind_bounds_of_cast(cx, source, e);
        }
        expr_copy(expr) => {
            // Note: This is the only place where we must check whether the
            // argument is copyable.  This is not because this is the only
            // kind of expression that may copy things, but rather because all
            // other copies will have been converted to moves by by the
            // `moves` pass if the value is not copyable.
            check_copy(cx,
                       ty::expr_ty(cx.tcx, expr),
                       expr.span,
                       "explicit copy requires a copyable argument");
        }
        expr_repeat(element, count_expr, _) => {
            let count = ty::eval_repeat_count(cx.tcx, count_expr, e.span);
            if count > 1 {
                let element_ty = ty::expr_ty(cx.tcx, element);
                check_copy(cx, element_ty, element.span,
                           "repeated element will be copied");
            }
        }
        _ => {}
    }
    visit::visit_expr(e, cx, v);
}

fn check_ty(aty: @Ty, cx: ctx, v: visit::vt<ctx>) {
    match aty.node {
      ty_path(_, id) => {
        do option::iter(&cx.tcx.node_type_substs.find(&id)) |ts| {
            let did = ast_util::def_id_of_def(cx.tcx.def_map.get(&id));
            let bounds = ty::lookup_item_type(cx.tcx, did).bounds;
            for vec::each2(*ts, *bounds) |ty, bound| {
                check_bounds(cx, aty.id, aty.span, *ty, *bound)
            }
        }
      }
      _ => {}
    }
    visit::visit_ty(aty, cx, v);
}

pub fn check_bounds(cx: ctx, id: node_id, sp: span,
                    ty: ty::t, bounds: ty::param_bounds) {
    let kind = ty::type_kind(cx.tcx, ty);
    let p_kind = ty::param_bounds_to_kind(bounds);
    if !ty::kind_lteq(p_kind, kind) {
        // If the only reason the kind check fails is because the
        // argument type isn't implicitly copyable, consult the warning
        // settings to figure out what to do.
        let implicit = ty::kind_implicitly_copyable() - ty::kind_copyable();
        if ty::kind_lteq(p_kind, kind | implicit) {
            cx.tcx.sess.span_lint(
                non_implicitly_copyable_typarams,
                id, cx.current_item, sp,
                ~"instantiating copy type parameter with a \
                 not implicitly copyable type");
        } else {
            cx.tcx.sess.span_err(
                sp,
                ~"instantiating a type parameter with an incompatible type " +
                ~"(needs `" + kind_to_str(p_kind) +
                ~"`, got `" + kind_to_str(kind) +
                ~"`, missing `" + kind_to_str(p_kind - kind) + ~"`)");
        }
    }
}

fn is_nullary_variant(cx: ctx, ex: @expr) -> bool {
    match ex.node {
      expr_path(_) => {
        match cx.tcx.def_map.get(&ex.id) {
          def_variant(edid, vdid) => {
            vec::len(ty::enum_variant_with_id(cx.tcx, edid, vdid).args) == 0u
          }
          _ => false
        }
      }
      _ => false
    }
}

fn check_imm_free_var(cx: ctx, def: def, sp: span) {
    match def {
        def_local(_, is_mutbl) => {
            if is_mutbl {
                cx.tcx.sess.span_err(
                    sp,
                    ~"mutable variables cannot be implicitly captured");
            }
        }
        def_arg(*) => { /* ok */ }
        def_upvar(_, def1, _, _) => { check_imm_free_var(cx, *def1, sp); }
        def_binding(*) | def_self(*) => { /*ok*/ }
        _ => {
            cx.tcx.sess.span_bug(
                sp,
                fmt!("unknown def for free variable: %?", def));
        }
    }
}

fn check_copy(cx: ctx, ty: ty::t, sp: span, reason: &str) {
    let k = ty::type_kind(cx.tcx, ty);
    if !ty::kind_can_be_copied(k) {
        cx.tcx.sess.span_err(sp, ~"copying a noncopyable value");
        cx.tcx.sess.span_note(sp, fmt!("%s", reason));
    }
}

pub fn check_send(cx: ctx, ty: ty::t, sp: span) -> bool {
    if !ty::kind_can_be_sent(ty::type_kind(cx.tcx, ty)) {
        cx.tcx.sess.span_err(sp, ~"not a sendable value");
        false
    } else {
        true
    }
}

// note: also used from middle::typeck::regionck!
pub fn check_durable(tcx: ty::ctxt, ty: ty::t, sp: span) -> bool {
    if !ty::kind_is_durable(ty::type_kind(tcx, ty)) {
        match ty::get(ty).sty {
          ty::ty_param(*) => {
            tcx.sess.span_err(sp, ~"value may contain borrowed \
                                    pointers; use `&static` bound");
          }
          _ => {
            tcx.sess.span_err(sp, ~"value may contain borrowed \
                                    pointers");
          }
        }
        false
    } else {
        true
    }
}

/// This is rather subtle.  When we are casting a value to a
/// instantiated trait like `a as trait/&r`, regionck already ensures
/// that any borrowed pointers that appear in the type of `a` are
/// bounded by `&r`.  However, it is possible that there are *type
/// parameters* in the type of `a`, and those *type parameters* may
/// have borrowed pointers within them.  We have to guarantee that the
/// regions which appear in those type parameters are not obscured.
///
/// Therefore, we ensure that one of three conditions holds:
///
/// (1) The trait instance cannot escape the current fn.  This is
/// guaranteed if the region bound `&r` is some scope within the fn
/// itself.  This case is safe because whatever borrowed pointers are
/// found within the type parameter, they must enclose the fn body
/// itself.
///
/// (2) The type parameter appears in the type of the trait.  For
/// example, if the type parameter is `T` and the trait type is
/// `deque<T>`, then whatever borrowed ptrs may appear in `T` also
/// appear in `deque<T>`.
///
/// (3) The type parameter is owned (and therefore does not contain
/// borrowed ptrs).
pub fn check_cast_for_escaping_regions(
    cx: ctx,
    source: @expr,
    target: @expr) {

    // Determine what type we are casting to; if it is not an trait, then no
    // worries.
    let target_ty = ty::expr_ty(cx.tcx, target);
    let target_substs = match ty::get(target_ty).sty {
      ty::ty_trait(_, ref substs, _) => {(/*bad*/copy *substs)}
      _ => { return; /* not a cast to a trait */ }
    };

    // Check, based on the region associated with the trait, whether it can
    // possibly escape the enclosing fn item (note that all type parameters
    // must have been declared on the enclosing fn item):
    match target_substs.self_r {
      Some(ty::re_scope(*)) => { return; /* case (1) */ }
      None | Some(ty::re_static) | Some(ty::re_free(*)) => {}
      Some(ty::re_bound(*)) | Some(ty::re_infer(*)) => {
        cx.tcx.sess.span_bug(
            source.span,
            fmt!("bad region found in kind: %?", target_substs.self_r));
      }
    }

    // Assuming the trait instance can escape, then ensure that each parameter
    // either appears in the trait type or is owned:
    let target_params = ty::param_tys_in_type(target_ty);
    let source_ty = ty::expr_ty(cx.tcx, source);
    do ty::walk_ty(source_ty) |ty| {
        match ty::get(ty).sty {
          ty::ty_param(source_param) => {
            if target_params.contains(&source_param) {
                /* case (2) */
            } else {
                check_durable(cx.tcx, ty, source.span); /* case (3) */
            }
          }
          _ => {}
        }
    }
}

/// Ensures that values placed into a ~Trait are copyable and sendable.
pub fn check_kind_bounds_of_cast(cx: ctx, source: @expr, target: @expr) {
    let target_ty = ty::expr_ty(cx.tcx, target);
    match ty::get(target_ty).sty {
        ty::ty_trait(_, _, ty::vstore_uniq) => {
            let source_ty = ty::expr_ty(cx.tcx, source);
            let source_kind = ty::type_kind(cx.tcx, source_ty);
            if !ty::kind_can_be_copied(source_kind) {
                cx.tcx.sess.span_err(target.span,
                    ~"uniquely-owned trait objects must be copyable");
            }
            if !ty::kind_can_be_sent(source_kind) {
                cx.tcx.sess.span_err(target.span,
                    ~"uniquely-owned trait objects must be sendable");
            }
        }
        _ => {} // Nothing to do.
    }
}

//
// Local Variables:
// mode: rust
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End:
//