new rules for merging expected/supplied types in closure signatures

Also, fix numbering in mir-opt tests. We are now anonymizing more
consistently, I think, and hence some of the `TyAnon` indices shifted.

src/test/compile-fail/closure-expected-type/README.md

@@ -0,0 +1 @@
+See `src/test/run-pass/closure-expected-type`.

src/test/compile-fail/closure-expected-type/expect-fn-supply-fn-multiple.rs

@@ -0,0 +1,49 @@
+// Copyright 2016 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.
+
+// must-compile-successfully
+
+#![feature(underscore_lifetimes)]
+#![allow(warnings)]
+
+type Different<'a, 'b> = &'a mut (&'a (), &'b ());
+type Same<'a> = Different<'a, 'a>;
+
+fn with_closure_expecting_different<F>(_: F)
+    where F: for<'a, 'b> FnOnce(Different<'a, 'b>)
+{
+}
+
+fn with_closure_expecting_different_anon<F>(_: F)
+    where F: FnOnce(Different<'_, '_>)
+{
+}
+
+fn supplying_nothing_expecting_anon() {
+    with_closure_expecting_different_anon(|x: Different| {
+    })
+}
+
+fn supplying_nothing_expecting_named() {
+    with_closure_expecting_different(|x: Different| {
+    })
+}
+
+fn supplying_underscore_expecting_anon() {
+    with_closure_expecting_different_anon(|x: Different<'_, '_>| {
+    })
+}
+
+fn supplying_underscore_expecting_named() {
+    with_closure_expecting_different(|x: Different<'_, '_>| {
+    })
+}
+
+fn main() { }

src/test/compile-fail/closure-expected-type/expect-fn-supply-fn.rs

@@ -0,0 +1,70 @@
+// Copyright 2016 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.
+
+#![feature(underscore_lifetimes)]
+
+fn with_closure_expecting_fn_with_free_region<F>(_: F)
+    where F: for<'a> FnOnce(fn(&'a u32), &i32)
+{
+}
+
+fn with_closure_expecting_fn_with_bound_region<F>(_: F)
+    where F: FnOnce(fn(&u32), &i32)
+{
+}
+
+fn expect_free_supply_free_from_fn<'x>(x: &'x u32) {
+    // Here, the type given for `'x` "obscures" a region from the
+    // expected signature that is bound at closure level.
+    with_closure_expecting_fn_with_free_region(|x: fn(&'x u32), y| {});
+    //~^ ERROR mismatched types
+    //~| ERROR mismatched types
+}
+
+fn expect_free_supply_free_from_closure() {
+    // A variant on the previous test. Here, the region `'a` will be
+    // bound at the closure level, just as is expected, so no error
+    // results.
+    type Foo<'a> = fn(&'a u32);
+    with_closure_expecting_fn_with_free_region(|_x: Foo<'_>, y| {});
+}
+
+fn expect_free_supply_bound() {
+    // Here, we are given a function whose region is bound at closure level,
+    // but we expect one bound in the argument. Error results.
+    with_closure_expecting_fn_with_free_region(|x: fn(&u32), y| {});
+    //~^ ERROR mismatched types
+}
+
+fn expect_bound_supply_free_from_fn<'x>(x: &'x u32) {
+    // Here, we are given a `fn(&u32)` but we expect a `fn(&'x
+    // u32)`. In principle, this could be ok, but we demand equality.
+    with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
+    //~^ ERROR mismatched types
+}
+
+fn expect_bound_supply_free_from_closure() {
+    // A variant on the previous test. Here, the region `'a` will be
+    // bound at the closure level, but we expect something bound at
+    // the argument level.
+    type Foo<'a> = fn(&'a u32);
+    with_closure_expecting_fn_with_bound_region(|_x: Foo<'_>, y| {});
+    //~^ ERROR mismatched types
+}
+
+fn expect_bound_supply_bound<'x>(x: &'x u32) {
+    // No error in this case. The supplied type supplies the bound
+    // regions, and hence we are able to figure out the type of `y`
+    // from the expected type
+    with_closure_expecting_fn_with_bound_region(|x: for<'z> fn(&'z u32), y| {
+    });
+}
+
+fn main() { }

src/test/compile-fail/closure-expected-type/expect-infer-var-appearing-twice.rs

@@ -0,0 +1,35 @@
+// Copyright 2016 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.
+
+fn with_closure<F, A>(_: F)
+    where F: FnOnce(A, A)
+{
+}
+
+fn a() {
+    with_closure(|x: u32, y| {
+        // We deduce type of `y` from `x`.
+    });
+}
+
+fn b() {
+    // Here we take the supplied types, resulting in an error later on.
+    with_closure(|x: u32, y: i32| {
+        //~^ ERROR mismatched types
+    });
+}
+
+fn c() {
+    with_closure(|x, y: i32| {
+        // We deduce type of `x` from `y`.
+    });
+}
+
+fn main() { }

src/test/compile-fail/closure-expected-type/expect-infer-var-supply-ty-with-bound-region.rs

@@ -0,0 +1,29 @@
+// Copyright 2016 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.
+
+// must-compile-successfully
+
+fn with_closure<F, A>(_: F)
+    where F: FnOnce(A, &u32)
+{
+}
+
+fn foo() {
+    // This version works; we infer `A` to be `u32`, and take the type
+    // of `y` to be `&u32`.
+    with_closure(|x: u32, y| {});
+}
+
+fn bar() {
+    // This version also works.
+    with_closure(|x: &u32, y| {});
+}
+
+fn main() { }

src/test/compile-fail/closure-expected-type/expect-infer-var-supply-ty-with-free-region.rs

@@ -0,0 +1,29 @@
+// Copyright 2016 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.
+
+// must-compile-successfully
+
+fn with_closure<F, A>(_: F)
+    where F: FnOnce(A, &u32)
+{
+}
+
+fn foo() {
+    // This version works; we infer `A` to be `u32`, and take the type
+    // of `y` to be `&u32`.
+    with_closure(|x: u32, y| {});
+}
+
+fn bar<'x>(x: &'x u32) {
+    // Same.
+    with_closure(|x: &'x u32, y| {});
+}
+
+fn main() { }

src/test/compile-fail/closure-expected-type/expect-region-supply-region.rs

@@ -0,0 +1,80 @@
+// Copyright 2016 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.
+
+#![allow(warnings)]
+
+fn closure_expecting_bound<F>(_: F)
+    where F: FnOnce(&u32)
+{
+}
+
+fn closure_expecting_free<'a, F>(_: F)
+    where F: FnOnce(&'a u32)
+{
+}
+
+fn expect_bound_supply_nothing() {
+    // Because `x` is inferred to have a bound region, we cannot allow
+    // it to escape into `f`:
+    let mut f: Option<&u32> = None;
+    closure_expecting_bound(|x| {
+        f = Some(x); //~ ERROR E0495
+    });
+}
+
+fn expect_bound_supply_bound() {
+    // Because `x` is inferred to have a bound region, we cannot allow
+    // it to escape into `f`, even with an explicit type annotation on
+    // closure:
+    let mut f: Option<&u32> = None;
+    closure_expecting_bound(|x: &u32| {
+        f = Some(x); //~ ERROR E0495
+    });
+}
+
+fn expect_bound_supply_named<'x>() {
+    let mut f: Option<&u32> = None;
+
+    // Here we give a type annotation that `x` should be free. We get
+    // an error because of that.
+    closure_expecting_bound(|x: &'x u32| {
+        //~^ ERROR mismatched types
+        //~| ERROR mismatched types
+
+        // And we still cannot let `x` escape into `f`.
+        f = Some(x);
+        //~^ ERROR cannot infer
+    });
+}
+
+fn expect_free_supply_nothing() {
+    let mut f: Option<&u32> = None;
+    closure_expecting_free(|x| f = Some(x)); // OK
+}
+
+fn expect_free_supply_bound() {
+    let mut f: Option<&u32> = None;
+
+    // Here, even though the annotation `&u32` could be seen as being
+    // bound in the closure, we permit it to be defined as a free
+    // region (which is inferred to something in the fn body).
+    closure_expecting_free(|x: &u32| f = Some(x)); // OK
+}
+
+fn expect_free_supply_named<'x>() {
+    let mut f: Option<&u32> = None;
+
+    // Here, even though the annotation `&u32` could be seen as being
+    // bound in the closure, we permit it to be defined as a free
+    // region (which is inferred to something in the fn body).
+    closure_expecting_free(|x: &'x u32| f = Some(x)); // OK
+}
+
+fn main() { }

src/test/compile-fail/closure-expected-type/expect-two-infer-vars-supply-ty-with-bound-region.rs

@@ -0,0 +1,29 @@
+// Copyright 2016 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.
+
+fn with_closure<F, A, B>(_: F)
+    where F: FnOnce(A, B)
+{
+}
+
+fn a() {
+    // Type of `y` is unconstrained.
+    with_closure(|x: u32, y| {}); //~ ERROR E0282
+}
+
+fn b() {
+    with_closure(|x: u32, y: u32| {}); // OK
+}
+
+fn c() {
+    with_closure(|x: u32, y: u32| {}); // OK
+}
+
+fn main() { }

src/test/mir-opt/validate_1.rs

@@ -62,7 +62,7 @@ fn main() {
 // fn main::{{closure}}(_1: &ReErased [closure@NodeId(50)], _2: &ReErased mut i32) -> i32 {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:11) => validate_1[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(50)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:11) => validate_1[317d]::main[0]::{{closure}}[0] }, BrAnon(1)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:11) => validate_1[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(50)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:11) => validate_1[317d]::main[0]::{{closure}}[0] }, BrAnon(0)) mut i32]);
 //         StorageLive(_3);
 //         Validate(Suspend(ReScope(Remainder(BlockRemainder { block: ItemLocalId(22), first_statement_index: 0 }))), [(*_2): i32]);
 //         _3 = &ReErased (*_2);

src/test/mir-opt/validate_4.rs

@@ -78,8 +78,8 @@ fn main() {
 // fn main::{{closure}}(_1: &ReErased [closure@NodeId(60)], _2: &ReErased mut i32) -> bool {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(60)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrAnon(1)) mut i32]);
-//         Validate(Release, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(60)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrAnon(1)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(60)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrAnon(0)) mut i32]);
+//         Validate(Release, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(60)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrAnon(0)) mut i32]);
 //         StorageLive(_3);
 //         ...
 //         _0 = const write_42(_3) -> bb1;

src/test/mir-opt/validate_5.rs

@@ -49,7 +49,7 @@ fn main() {
 // fn main::{{closure}}(_1: &ReErased [closure@NodeId(46)], _2: &ReErased mut i32) -> bool {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:9) => validate_5[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(46)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:9) => validate_5[317d]::main[0]::{{closure}}[0] }, BrAnon(1)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:9) => validate_5[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(46)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:9) => validate_5[317d]::main[0]::{{closure}}[0] }, BrAnon(0)) mut i32]);
 //         StorageLive(_3);
 //         StorageLive(_4);
 //         Validate(Suspend(ReScope(Node(ItemLocalId(9)))), [(*_2): i32]);

src/test/run-pass/closure-expected-type/README.md

@@ -0,0 +1,8 @@
+Some tests targeted at how we deduce the types of closure arguments.
+This process is a result of some heuristics aimed at combining the
+*expected type* we have with the *actual types* that we get from
+inputs. This investigation was kicked off by #38714, which revealed
+some pretty deep flaws in the ad-hoc way that we were doing things
+before.
+
+See also `src/test/compile-fail/closure-expected-type`.

src/test/run-pass/closure-expected-type/expect-infer-supply-two-infers.rs

@@ -0,0 +1,26 @@
+// Copyright 2016 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.
+
+fn with_closure<A, F>(_: F)
+    where F: FnOnce(Vec<A>, A)
+{
+}
+
+fn expect_free_supply_free<'x>(x: &'x u32) {
+    with_closure(|mut x: Vec<_>, y| {
+        // Shows that the call to `x.push()` is influencing type of `y`...
+        x.push(22_u32);
+
+        // ...since we now know the type of `y` and can resolve the method call.
+        y.wrapping_add(1);
+    });
+}
+
+fn main() { }

src/test/run-pass/closure-expected-type/issue-38714.rs

@@ -0,0 +1,26 @@
+// Copyright 2016 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.
+
+struct UsizeRef<'a> {
+    a: &'a usize
+}
+
+type RefTo = Box<for<'r> Fn(&'r Vec<usize>) -> UsizeRef<'r>>;
+
+fn ref_to<'a>(vec: &'a Vec<usize>) -> UsizeRef<'a> {
+    UsizeRef{ a: &vec[0]}
+}
+
+fn main() {
+    // Regression test: this was causing ICEs; it should compile.
+    let a: RefTo = Box::new(|vec: &Vec<usize>| {
+        UsizeRef{ a: &vec[0] }
+    });
+}

src/test/run-pass/closure-expected-type/supply-just-return-type.rs

@@ -0,0 +1,35 @@
+// Copyright 2016 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.
+
+fn with_closure<F, R>(f: F) -> Result<char, R>
+    where F: FnOnce(&char) -> Result<char, R>,
+{
+    f(&'a')
+}
+
+fn main() {
+    // Test that supplying the `-> Result<char, ()>` manually here
+    // (which is needed to constrain `R`) still allows us to figure
+    // out that the type of `x` is `&'a char` where `'a` is bound in
+    // the closure (if we didn't, we'd get a type-error because
+    // `with_closure` requires a bound region).
+    //
+    // This pattern was found in the wild.
+    let z = with_closure(|x| -> Result<char, ()> { Ok(*x) });
+    assert_eq!(z.unwrap(), 'a');
+
+    // It also works with `_`:
+    let z = with_closure(|x: _| -> Result<char, ()> { Ok(*x) });
+    assert_eq!(z.unwrap(), 'a');
+
+    // It also works with `&_`:
+    let z = with_closure(|x: &_| -> Result<char, ()> { Ok(*x) });
+    assert_eq!(z.unwrap(), 'a');
+}

src/test/run-pass/closure-expected-type/supply-nothing.rs

@@ -0,0 +1,20 @@
+// Copyright 2016 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.
+
+fn with_closure<F>(f: F) -> u32
+    where F: FnOnce(&u32, &u32) -> u32
+{
+    f(&22, &44)
+}
+
+fn main() {
+    let z = with_closure(|x, y| x + y).wrapping_add(1);
+    assert_eq!(z, 22 + 44 + 1);
+}