Auto merge of #51564 - SimonSapin:try-int, r=alexcrichton

Implement always-fallible TryFrom for usize/isize conversions that are infallible on some platforms

This reverts commit 837d6c70233715a0ae8e15c703d40e3046a2f36a "Remove TryFrom impls that might become conditionally-infallible with a portability lint".

This fixes #49415 by adding (restoring) missing `TryFrom` impls for integer conversions to or from `usize` or `isize`, by making them always fallible at the type system level (that is, with `Error=TryFromIntError`) even though they happen to be infallible on some platforms (for some values of `size_of::<usize>()`).

They had been removed to allow the possibility to conditionally having some of them be infallible `From` impls instead, depending on the platforms, and have the [portability lint](https://github.com/rust-lang/rfcs/pull/1868) warn when they are used in code that is not already opting into non-portability. For example `#[allow(some_lint)] usize::from(x: u64)` would be valid on code that only targets 64-bit platforms.

This PR gives up on this possiblity for two reasons:

* Based on discussion with @aturon, it seems that the portability lint is not happening any time soon. It’s better to have the conversions be available *at all* than keep blocking them for so long. Portability-lint-gated platform-specific APIs can always be added separately later.

* For code that is fine with fallibility, the alternative would force it to opt into "non-portability" even though there would be no real portability issue.

1 files changed, 127 insertions, 0 deletions

diff --git a/src/libcore/tests/num/mod.rs b/src/libcore/tests/num/mod.rs
index 24fe96a2b82..ab96d3126bb 100644
--- a/src/libcore/tests/num/mod.rs
+++ b/src/libcore/tests/num/mod.rs
@@ -37,6 +37,15 @@ mod flt2dec;
 mod dec2flt;
 mod bignum;
 
+
+/// Adds the attribute to all items in the block.
+macro_rules! cfg_block {
+    ($(#[$attr:meta]{$($it:item)*})*) => {$($(
+        #[$attr]
+        $it
+    )*)*}
+}
+
 /// Groups items that assume the pointer width is either 16/32/64, and has to be altered if
 /// support for larger/smaller pointer widths are added in the future.
 macro_rules! assume_usize_width {
@@ -330,6 +339,42 @@ assume_usize_width! {
 
     test_impl_try_from_always_ok! { test_try_u16usize, u16, usize }
     test_impl_try_from_always_ok! { test_try_i16isize, i16, isize }
+
+    test_impl_try_from_always_ok! { test_try_usizeu64, usize, u64 }
+    test_impl_try_from_always_ok! { test_try_usizeu128, usize, u128 }
+    test_impl_try_from_always_ok! { test_try_usizei128, usize, i128 }
+
+    test_impl_try_from_always_ok! { test_try_isizei64, isize, i64 }
+    test_impl_try_from_always_ok! { test_try_isizei128, isize, i128 }
+
+    cfg_block!(
+        #[cfg(target_pointer_width = "16")] {
+            test_impl_try_from_always_ok! { test_try_usizeu16, usize, u16 }
+            test_impl_try_from_always_ok! { test_try_isizei16, isize, i16 }
+            test_impl_try_from_always_ok! { test_try_usizeu32, usize, u32 }
+            test_impl_try_from_always_ok! { test_try_usizei32, usize, i32 }
+            test_impl_try_from_always_ok! { test_try_isizei32, isize, i32 }
+            test_impl_try_from_always_ok! { test_try_usizei64, usize, i64 }
+        }
+
+        #[cfg(target_pointer_width = "32")] {
+            test_impl_try_from_always_ok! { test_try_u16isize, u16, isize }
+            test_impl_try_from_always_ok! { test_try_usizeu32, usize, u32 }
+            test_impl_try_from_always_ok! { test_try_isizei32, isize, i32 }
+            test_impl_try_from_always_ok! { test_try_u32usize, u32, usize }
+            test_impl_try_from_always_ok! { test_try_i32isize, i32, isize }
+            test_impl_try_from_always_ok! { test_try_usizei64, usize, i64 }
+        }
+
+        #[cfg(target_pointer_width = "64")] {
+            test_impl_try_from_always_ok! { test_try_u16isize, u16, isize }
+            test_impl_try_from_always_ok! { test_try_u32usize, u32, usize }
+            test_impl_try_from_always_ok! { test_try_u32isize, u32, isize }
+            test_impl_try_from_always_ok! { test_try_i32isize, i32, isize }
+            test_impl_try_from_always_ok! { test_try_u64usize, u64, usize }
+            test_impl_try_from_always_ok! { test_try_i64isize, i64, isize }
+        }
+    );
 }
 
 /// Conversions where max of $source can be represented as $target,
@@ -378,6 +423,24 @@ assume_usize_width! {
     test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu64, isize, u64 }
     test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu128, isize, u128 }
     test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeusize, isize, usize }
+
+    cfg_block!(
+        #[cfg(target_pointer_width = "16")] {
+            test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu16, isize, u16 }
+            test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu32, isize, u32 }
+        }
+
+        #[cfg(target_pointer_width = "32")] {
+            test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu32, isize, u32 }
+
+            test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_i32usize, i32, usize }
+        }
+
+        #[cfg(target_pointer_width = "64")] {
+            test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_i32usize, i32, usize }
+            test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_i64usize, i64, usize }
+        }
+    );
 }
 
 /// Conversions where max of $source can not be represented as $target,
@@ -419,9 +482,29 @@ test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u128i64, u128, i64 }
 test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u128i128, u128, i128 }
 
 assume_usize_width! {
+    test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u64isize, u64, isize }
+    test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u128isize, u128, isize }
+
     test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei8, usize, i8 }
     test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei16, usize, i16 }
     test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizeisize, usize, isize }
+
+    cfg_block!(
+        #[cfg(target_pointer_width = "16")] {
+            test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u16isize, u16, isize }
+            test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u32isize, u32, isize }
+        }
+
+        #[cfg(target_pointer_width = "32")] {
+            test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u32isize, u32, isize }
+            test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei32, usize, i32 }
+        }
+
+        #[cfg(target_pointer_width = "64")] {
+            test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei32, usize, i32 }
+            test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei64, usize, i64 }
+        }
+    );
 }
 
 /// Conversions where min/max of $source can not be represented as $target.
@@ -481,6 +564,34 @@ test_impl_try_from_same_sign_err! { test_try_i128i64, i128, i64 }
 
 assume_usize_width! {
     test_impl_try_from_same_sign_err! { test_try_usizeu8, usize, u8 }
+    test_impl_try_from_same_sign_err! { test_try_u128usize, u128, usize }
+    test_impl_try_from_same_sign_err! { test_try_i128isize, i128, isize }
+
+    cfg_block!(
+        #[cfg(target_pointer_width = "16")] {
+            test_impl_try_from_same_sign_err! { test_try_u32usize, u32, usize }
+            test_impl_try_from_same_sign_err! { test_try_u64usize, u64, usize }
+
+            test_impl_try_from_same_sign_err! { test_try_i32isize, i32, isize }
+            test_impl_try_from_same_sign_err! { test_try_i64isize, i64, isize }
+        }
+
+        #[cfg(target_pointer_width = "32")] {
+            test_impl_try_from_same_sign_err! { test_try_u64usize, u64, usize }
+            test_impl_try_from_same_sign_err! { test_try_usizeu16, usize, u16 }
+
+            test_impl_try_from_same_sign_err! { test_try_i64isize, i64, isize }
+            test_impl_try_from_same_sign_err! { test_try_isizei16, isize, i16 }
+        }
+
+        #[cfg(target_pointer_width = "64")] {
+            test_impl_try_from_same_sign_err! { test_try_usizeu16, usize, u16 }
+            test_impl_try_from_same_sign_err! { test_try_usizeu32, usize, u32 }
+
+            test_impl_try_from_same_sign_err! { test_try_isizei16, isize, i16 }
+            test_impl_try_from_same_sign_err! { test_try_isizei32, isize, i32 }
+        }
+    );
 }
 
 /// Conversions where neither the min nor the max of $source can be represented by
@@ -525,6 +636,22 @@ test_impl_try_from_signed_to_unsigned_err! { test_try_i128u64, i128, u64 }
 assume_usize_width! {
     test_impl_try_from_signed_to_unsigned_err! { test_try_isizeu8, isize, u8 }
     test_impl_try_from_signed_to_unsigned_err! { test_try_i128usize, i128, usize }
+
+    cfg_block! {
+        #[cfg(target_pointer_width = "16")] {
+            test_impl_try_from_signed_to_unsigned_err! { test_try_i32usize, i32, usize }
+            test_impl_try_from_signed_to_unsigned_err! { test_try_i64usize, i64, usize }
+        }
+        #[cfg(target_pointer_width = "32")] {
+            test_impl_try_from_signed_to_unsigned_err! { test_try_i64usize, i64, usize }
+
+            test_impl_try_from_signed_to_unsigned_err! { test_try_isizeu16, isize, u16 }
+        }
+        #[cfg(target_pointer_width = "64")] {
+            test_impl_try_from_signed_to_unsigned_err! { test_try_isizeu16, isize, u16 }
+            test_impl_try_from_signed_to_unsigned_err! { test_try_isizeu32, isize, u32 }
+        }
+    }
 }
 
 macro_rules! test_float {