Rollup merge of #140593 - m-ou-se:some-temp, r=Nadrieril

Temporary lifetime extension through tuple struct and tuple variant constructors

This makes temporary lifetime extension work for tuple struct and tuple variant constructors, such as `Some()`.

Before:
```rust
let a = &temp(); // Extended
let a = Some(&temp()); // Not extended :(
let a = Some { 0: &temp() }; // Extended
```

After:
```rust
let a = &temp(); // Extended
let a = Some(&temp()); // Extended
let a = Some { 0: &temp() }; // Extended
```

So, with this change, this works:

```rust
let a = Some(&String::from("hello")); // New: String lifetime now extended!

println!("{a:?}");
```

Until now, we did not extend through tuple struct/variant constructors (like `Some`), because they are function calls syntactically, and we do not want to extend the String lifetime in:

```rust
let a = some_function(&String::from("hello")); // String not extended!
```

However, it turns out to be very easy to distinguish between regular functions and constructors at the point where we do lifetime extension.

In practice, constructors nearly always use UpperCamelCase while regular functions use lower_snake_case, so it should still be easy to for a human programmer at the call site to see whether something qualifies for lifetime extension or not.

This needs a lang fcp.

---

More examples of what will work after this change:

```rust
let x = Person {
    name: "Ferris",
    job: Some(&Job { // `Job` now extended!
        title: "Chief Rustacean",
        organisation: "Acme Ltd.",
    }),
};

dbg!(x);
```

```rust
let file = if use_stdout {
    None
} else {
    Some(&File::create("asdf")?) // `File` now extended!
};

set_logger(file);
```

```rust
use std::path::Component;

let c = Component::Normal(&OsString::from(format!("test-{num}"))); // OsString now extended!

assert_eq!(path.components.first().unwrap(), c);
```

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/check/region.rs

@@ -10,6 +10,7 @@ use std::mem;
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
+use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::{Arm, Block, Expr, LetStmt, Pat, PatKind, Stmt};
@@ -752,13 +753,19 @@ fn resolve_local<'tcx>(
                     record_rvalue_scope_if_borrow_expr(visitor, arm.body, blk_id);
                 }
             }
-            hir::ExprKind::Call(..) | hir::ExprKind::MethodCall(..) => {
-                // FIXME(@dingxiangfei2009): choose call arguments here
-                // for candidacy for extended parameter rule application
-            }
-            hir::ExprKind::Index(..) => {
-                // FIXME(@dingxiangfei2009): select the indices
-                // as candidate for rvalue scope rules
+            hir::ExprKind::Call(func, args) => {
+                // Recurse into tuple constructors, such as `Some(&temp())`.
+                //
+                // That way, there is no difference between `Some(..)` and `Some { 0: .. }`,
+                // even though the former is syntactically a function call.
+                if let hir::ExprKind::Path(path) = &func.kind
+                    && let hir::QPath::Resolved(None, path) = path
+                    && let Res::SelfCtor(_) | Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) = path.res
+                {
+                    for arg in args {
+                        record_rvalue_scope_if_borrow_expr(visitor, arg, blk_id);
+                    }
+                }
             }
             _ => {}
         }

src/tools/tidy/src/issues.txt

@@ -754,7 +754,6 @@ ui/consts/issue-46553.rs
 ui/consts/issue-47789.rs
 ui/consts/issue-50439.rs
 ui/consts/issue-52023-array-size-pointer-cast.rs
-ui/consts/issue-54224.rs
 ui/consts/issue-54348.rs
 ui/consts/issue-54387.rs
 ui/consts/issue-54582.rs

tests/ui/consts/const-mut-refs/mut_ref_in_final.rs

@@ -18,7 +18,7 @@ const B: *mut i32 = &mut 4; //~ ERROR mutable references are not allowed
 const B2: Option<&mut i32> = None;
 
 // Not ok, can't prove that no mutable allocation ends up in final value
-const B3: Option<&mut i32> = Some(&mut 42); //~ ERROR temporary value dropped while borrowed
+const B3: Option<&mut i32> = Some(&mut 42); //~ ERROR mutable references are not allowed
 
 const fn helper(x: &mut i32) -> Option<&mut i32> { Some(x) }
 const B4: Option<&mut i32> = helper(&mut 42); //~ ERROR temporary value dropped while borrowed

tests/ui/consts/const-mut-refs/mut_ref_in_final.stderr

@@ -4,15 +4,11 @@ error[E0764]: mutable references are not allowed in the final value of constants
 LL | const B: *mut i32 = &mut 4;
    |                     ^^^^^^
 
-error[E0716]: temporary value dropped while borrowed
-  --> $DIR/mut_ref_in_final.rs:21:40
+error[E0764]: mutable references are not allowed in the final value of constants
+  --> $DIR/mut_ref_in_final.rs:21:35
    |
 LL | const B3: Option<&mut i32> = Some(&mut 42);
-   |                              ----------^^-
-   |                              |         | |
-   |                              |         | temporary value is freed at the end of this statement
-   |                              |         creates a temporary value which is freed while still in use
-   |                              using this value as a constant requires that borrow lasts for `'static`
+   |                                   ^^^^^^^
 
 error[E0716]: temporary value dropped while borrowed
   --> $DIR/mut_ref_in_final.rs:24:42

tests/ui/consts/issue-54224.rs

@@ -3,10 +3,11 @@
 #![allow(unconditional_panic)]
 
 use std::cell::Cell;
+use std::convert::identity;
 use std::mem::ManuallyDrop;
 
 // We do not promote mutable references.
-static mut TEST1: Option<&mut [i32]> = Some(&mut [1, 2, 3]); //~ ERROR temporary value dropped while borrowed
+static mut TEST1: &mut [i32] = identity(&mut [1, 2, 3]); //~ ERROR temporary value dropped while borrowed
 
 static mut TEST2: &'static mut [i32] = {
     let x = &mut [1,2,3]; //~ ERROR temporary value dropped while borrowed

tests/ui/consts/issue-54224.stderr

@@ -1,15 +1,15 @@
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:9:50
+  --> $DIR/promote-not.rs:10:46
    |
-LL | static mut TEST1: Option<&mut [i32]> = Some(&mut [1, 2, 3]);
-   |                                        ----------^^^^^^^^^-
-   |                                        |         |        |
-   |                                        |         |        temporary value is freed at the end of this statement
-   |                                        |         creates a temporary value which is freed while still in use
-   |                                        using this value as a static requires that borrow lasts for `'static`
+LL | static mut TEST1: &mut [i32] = identity(&mut [1, 2, 3]);
+   |                                --------------^^^^^^^^^-
+   |                                |             |        |
+   |                                |             |        temporary value is freed at the end of this statement
+   |                                |             creates a temporary value which is freed while still in use
+   |                                using this value as a static requires that borrow lasts for `'static`
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:12:18
+  --> $DIR/promote-not.rs:13:18
    |
 LL |     let x = &mut [1,2,3];
    |                  ^^^^^^^ creates a temporary value which is freed while still in use
@@ -19,7 +19,7 @@ LL | };
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:34:29
+  --> $DIR/promote-not.rs:35:29
    |
 LL |     let _x: &'static i32 = &unsafe { U { x: 0 }.x };
    |             ------------    ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -29,7 +29,7 @@ LL | };
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:40:29
+  --> $DIR/promote-not.rs:41:29
    |
 LL |     let _val: &'static _ = &(Cell::new(1), 2).1;
    |               ----------    ^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -39,7 +39,7 @@ LL | };
    | - temporary value is freed at the end of this statement
 
 error[E0493]: destructor of `String` cannot be evaluated at compile-time
-  --> $DIR/promote-not.rs:47:14
+  --> $DIR/promote-not.rs:48:14
    |
 LL |     let x = &String::new();
    |              ^^^^^^^^^^^^^ the destructor for this type cannot be evaluated in constants
@@ -48,7 +48,7 @@ LL | };
    | - value is dropped here
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:59:33
+  --> $DIR/promote-not.rs:60:33
    |
 LL |         let _x: &'static u32 = &mk_panic();
    |                 ------------    ^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -58,7 +58,7 @@ LL |     }
    |     - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:21:32
+  --> $DIR/promote-not.rs:22:32
    |
 LL |         let _x: &'static () = &foo();
    |                 -----------    ^^^^^ creates a temporary value which is freed while still in use
@@ -68,7 +68,7 @@ LL |     }
    |     - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:29:29
+  --> $DIR/promote-not.rs:30:29
    |
 LL |     let _x: &'static i32 = &unsafe { U { x: 0 }.x };
    |             ------------    ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -78,7 +78,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:65:29
+  --> $DIR/promote-not.rs:66:29
    |
 LL |     let _val: &'static _ = &(Cell::new(1), 2).0;
    |               ----------    ^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -89,7 +89,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:66:29
+  --> $DIR/promote-not.rs:67:29
    |
 LL |     let _val: &'static _ = &(Cell::new(1), 2).1;
    |               ----------    ^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -100,7 +100,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:69:29
+  --> $DIR/promote-not.rs:70:29
    |
 LL |     let _val: &'static _ = &(1/0);
    |               ----------    ^^^^^ creates a temporary value which is freed while still in use
@@ -111,7 +111,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:70:29
+  --> $DIR/promote-not.rs:71:29
    |
 LL |     let _val: &'static _ = &(1/(1-1));
    |               ----------    ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -122,7 +122,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:71:29
+  --> $DIR/promote-not.rs:72:29
    |
 LL |     let _val: &'static _ = &((1+1)/(1-1));
    |               ----------    ^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -133,7 +133,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:72:29
+  --> $DIR/promote-not.rs:73:29
    |
 LL |     let _val: &'static _ = &(i32::MIN/-1);
    |               ----------    ^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -144,7 +144,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:73:29
+  --> $DIR/promote-not.rs:74:29
    |
 LL |     let _val: &'static _ = &(i32::MIN/(0-1));
    |               ----------    ^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -155,7 +155,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:74:29
+  --> $DIR/promote-not.rs:75:29
    |
 LL |     let _val: &'static _ = &(-128i8/-1);
    |               ----------    ^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -166,7 +166,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:75:29
+  --> $DIR/promote-not.rs:76:29
    |
 LL |     let _val: &'static _ = &(1%0);
    |               ----------    ^^^^^ creates a temporary value which is freed while still in use
@@ -177,7 +177,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:76:29
+  --> $DIR/promote-not.rs:77:29
    |
 LL |     let _val: &'static _ = &(1%(1-1));
    |               ----------    ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -188,7 +188,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:77:29
+  --> $DIR/promote-not.rs:78:29
    |
 LL |     let _val: &'static _ = &([1,2,3][4]+1);
    |               ----------    ^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -199,7 +199,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:81:29
+  --> $DIR/promote-not.rs:82:29
    |
 LL |     let _val: &'static _ = &TEST_DROP;
    |               ----------    ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -210,7 +210,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:83:29
+  --> $DIR/promote-not.rs:84:29
    |
 LL |     let _val: &'static _ = &&TEST_DROP;
    |               ----------    ^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -221,7 +221,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:83:30
+  --> $DIR/promote-not.rs:84:30
    |
 LL |     let _val: &'static _ = &&TEST_DROP;
    |               ----------     ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -232,7 +232,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:86:29
+  --> $DIR/promote-not.rs:87:29
    |
 LL |     let _val: &'static _ = &(&TEST_DROP,);
    |               ----------    ^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -243,7 +243,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:86:31
+  --> $DIR/promote-not.rs:87:31
    |
 LL |     let _val: &'static _ = &(&TEST_DROP,);
    |               ----------      ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -254,7 +254,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:89:29
+  --> $DIR/promote-not.rs:90:29
    |
 LL |     let _val: &'static _ = &[&TEST_DROP; 1];
    |               ----------    ^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -265,7 +265,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:89:31
+  --> $DIR/promote-not.rs:90:31
    |
 LL |     let _val: &'static _ = &[&TEST_DROP; 1];
    |               ----------      ^^^^^^^^^    - temporary value is freed at the end of this statement
@@ -274,7 +274,7 @@ LL |     let _val: &'static _ = &[&TEST_DROP; 1];
    |               type annotation requires that borrow lasts for `'static`
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:98:26
+  --> $DIR/promote-not.rs:99:26
    |
 LL |     let x: &'static _ = &UnionWithCell { f1: 0 };
    |            ----------    ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use

tests/ui/consts/promote-not.rs

@@ -43,8 +43,8 @@ fn main() {
     // Disallow impls which relates lifetimes in the coroutine interior
     let gen = #[coroutine] move || {
         let a = A(&mut true, &mut true, No);
-        //~^ ERROR temporary value dropped while borrowed
-        //~| ERROR temporary value dropped while borrowed
+        //~^ ERROR borrow may still be in use when coroutine yields
+        //~| ERROR borrow may still be in use when coroutine yields
         yield;
         assert_foo(a);
     };