Remove TryFrom impls that might become conditionally-infallible with a portability lint

https://github.com/rust-lang/rust/pull/49305#issuecomment-376293243

src/libcore/iter/range.rs

@@ -91,7 +91,7 @@ macro_rules! step_impl_unsigned {
             #[inline]
             #[allow(unreachable_patterns)]
             fn add_usize(&self, n: usize) -> Option<Self> {
-                match <$t>::try_from(n) {
+                match <$t>::private_try_from(n) {
                     Ok(n_as_t) => self.checked_add(n_as_t),
                     Err(_) => None,
                 }
@@ -123,7 +123,7 @@ macro_rules! step_impl_signed {
             #[inline]
             #[allow(unreachable_patterns)]
             fn add_usize(&self, n: usize) -> Option<Self> {
-                match <$unsigned>::try_from(n) {
+                match <$unsigned>::private_try_from(n) {
                     Ok(n_as_unsigned) => {
                         // Wrapping in unsigned space handles cases like
                         // `-120_i8.add_usize(200) == Some(80_i8)`,
@@ -461,3 +461,73 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
 
 #[stable(feature = "fused", since = "1.26.0")]
 impl<A: Step> FusedIterator for ops::RangeInclusive<A> {}
+
+/// Compensate removal of some impls per
+/// https://github.com/rust-lang/rust/pull/49305#issuecomment-376293243
+trait PrivateTryFromUsize: Sized {
+    fn private_try_from(n: usize) -> Result<Self, ()>;
+}
+
+impl<T> PrivateTryFromUsize for T where T: TryFrom<usize> {
+    #[inline]
+    fn private_try_from(n: usize) -> Result<Self, ()> {
+        T::try_from(n).map_err(|_| ())
+    }
+}
+
+// no possible bounds violation
+macro_rules! try_from_unbounded {
+    ($($target:ty),*) => {$(
+        impl PrivateTryFromUsize for $target {
+            #[inline]
+            fn private_try_from(value: usize) -> Result<Self, ()> {
+                Ok(value as $target)
+            }
+        }
+    )*}
+}
+
+// unsigned to signed (only positive bound)
+macro_rules! try_from_upper_bounded {
+    ($($target:ty),*) => {$(
+        impl PrivateTryFromUsize for $target {
+            #[inline]
+            fn private_try_from(u: usize) -> Result<$target, ()> {
+                if u > (<$target>::max_value() as usize) {
+                    Err(())
+                } else {
+                    Ok(u as $target)
+                }
+            }
+        }
+    )*}
+}
+
+
+#[cfg(target_pointer_width = "16")]
+mod ptr_try_from_impls {
+    use super::PrivateTryFromUsize;
+
+    try_from_unbounded!(u16, u32, u64, u128);
+    try_from_unbounded!(i32, i64, i128);
+}
+
+#[cfg(target_pointer_width = "32")]
+mod ptr_try_from_impls {
+    use super::PrivateTryFromUsize;
+
+    try_from_upper_bounded!(u16);
+    try_from_unbounded!(u32, u64, u128);
+    try_from_upper_bounded!(i32);
+    try_from_unbounded!(i64, i128);
+}
+
+#[cfg(target_pointer_width = "64")]
+mod ptr_try_from_impls {
+    use super::PrivateTryFromUsize;
+
+    try_from_upper_bounded!(u16, u32);
+    try_from_unbounded!(u64, u128);
+    try_from_upper_bounded!(i32, i64);
+    try_from_unbounded!(i128);
+}

src/libcore/num/mod.rs

@@ -3676,21 +3676,6 @@ impl From<!> for TryFromIntError {
     }
 }
 
-// no possible bounds violation
-macro_rules! try_from_unbounded {
-    ($source:ty, $($target:ty),*) => {$(
-        #[stable(feature = "try_from", since = "1.26.0")]
-        impl TryFrom<$source> for $target {
-            type Error = TryFromIntError;
-
-            #[inline]
-            fn try_from(value: $source) -> Result<Self, Self::Error> {
-                Ok(value as $target)
-            }
-        }
-    )*}
-}
-
 // only negative bounds
 macro_rules! try_from_lower_bounded {
     ($source:ty, $($target:ty),*) => {$(
@@ -3789,27 +3774,20 @@ try_from_both_bounded!(i128, u64, u32, u16, u8);
 try_from_upper_bounded!(usize, isize);
 try_from_lower_bounded!(isize, usize);
 
+try_from_upper_bounded!(usize, u8);
+try_from_upper_bounded!(usize, i8, i16);
+try_from_both_bounded!(isize, u8);
+try_from_both_bounded!(isize, i8);
+
 #[cfg(target_pointer_width = "16")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
     use convert::TryFrom;
 
-    try_from_upper_bounded!(usize, u8);
+    // Fallible across platfoms, only implementation differs
-    try_from_unbounded!(usize, u16, u32, u64, u128);
-    try_from_upper_bounded!(usize, i8, i16);
-    try_from_unbounded!(usize, i32, i64, i128);
-
-    try_from_both_bounded!(isize, u8);
     try_from_lower_bounded!(isize, u16, u32, u64, u128);
-    try_from_both_bounded!(isize, i8);
-    try_from_unbounded!(isize, i16, i32, i64, i128);
-
-    rev!(try_from_upper_bounded, usize, u32, u64, u128);
     rev!(try_from_lower_bounded, usize, i8, i16);
     rev!(try_from_both_bounded, usize, i32, i64, i128);
-
-    rev!(try_from_upper_bounded, isize, u16, u32, u64, u128);
-    rev!(try_from_both_bounded, isize, i32, i64, i128);
 }
 
 #[cfg(target_pointer_width = "32")]
@@ -3817,25 +3795,11 @@ mod ptr_try_from_impls {
     use super::TryFromIntError;
     use convert::TryFrom;
 
-    try_from_upper_bounded!(usize, u8, u16);
+    // Fallible across platfoms, only implementation differs
-    try_from_unbounded!(usize, u32, u64, u128);
+    try_from_both_bounded!(isize, u16);
-    try_from_upper_bounded!(usize, i8, i16, i32);
-    try_from_unbounded!(usize, i64, i128);
-
-    try_from_both_bounded!(isize, u8, u16);
     try_from_lower_bounded!(isize, u32, u64, u128);
-    try_from_both_bounded!(isize, i8, i16);
-    try_from_unbounded!(isize, i32, i64, i128);
-
-    rev!(try_from_unbounded, usize, u32);
-    rev!(try_from_upper_bounded, usize, u64, u128);
     rev!(try_from_lower_bounded, usize, i8, i16, i32);
     rev!(try_from_both_bounded, usize, i64, i128);
-
-    rev!(try_from_unbounded, isize, u16);
-    rev!(try_from_upper_bounded, isize, u32, u64, u128);
-    rev!(try_from_unbounded, isize, i32);
-    rev!(try_from_both_bounded, isize, i64, i128);
 }
 
 #[cfg(target_pointer_width = "64")]
@@ -3843,25 +3807,11 @@ mod ptr_try_from_impls {
     use super::TryFromIntError;
     use convert::TryFrom;
 
-    try_from_upper_bounded!(usize, u8, u16, u32);
+    // Fallible across platfoms, only implementation differs
-    try_from_unbounded!(usize, u64, u128);
+    try_from_both_bounded!(isize, u16, u32);
-    try_from_upper_bounded!(usize, i8, i16, i32, i64);
-    try_from_unbounded!(usize, i128);
-
-    try_from_both_bounded!(isize, u8, u16, u32);
     try_from_lower_bounded!(isize, u64, u128);
-    try_from_both_bounded!(isize, i8, i16, i32);
-    try_from_unbounded!(isize, i64, i128);
-
-    rev!(try_from_unbounded, usize, u32, u64);
-    rev!(try_from_upper_bounded, usize, u128);
     rev!(try_from_lower_bounded, usize, i8, i16, i32, i64);
     rev!(try_from_both_bounded, usize, i128);
-
-    rev!(try_from_unbounded, isize, u16, u32);
-    rev!(try_from_upper_bounded, isize, u64, u128);
-    rev!(try_from_unbounded, isize, i32, i64);
-    rev!(try_from_both_bounded, isize, i128);
 }
 
 #[doc(hidden)]

src/libcore/tests/num/mod.rs

@@ -37,15 +37,6 @@ 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 {
@@ -318,42 +309,6 @@ 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,
@@ -402,24 +357,6 @@ 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,
@@ -461,29 +398,9 @@ 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.
@@ -543,34 +460,6 @@ 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
@@ -615,22 +504,6 @@ 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 {

src/libstd/io/cursor.rs

@@ -10,7 +10,6 @@
 
 use io::prelude::*;
 
-use core::convert::TryInto;
 use cmp;
 use io::{self, Initializer, SeekFrom, Error, ErrorKind};
 
@@ -260,9 +259,26 @@ fn slice_write(pos_mut: &mut u64, slice: &mut [u8], buf: &[u8]) -> io::Result<us
     Ok(amt)
 }
 
+/// Compensate removal of some impls per
+/// https://github.com/rust-lang/rust/pull/49305#issuecomment-376293243
+#[cfg(any(target_pointer_width = "16",
+          target_pointer_width = "32"))]
+fn try_into(n: u64) -> Result<usize, ()> {
+    if n <= (<usize>::max_value() as u64) {
+        Ok(n as usize)
+    } else {
+        Err(())
+    }
+}
+
+#[cfg(any(target_pointer_width = "64"))]
+fn try_into(n: u64) -> Result<usize, ()> {
+    Ok(n as usize)
+}
+
 // Resizing write implementation
 fn vec_write(pos_mut: &mut u64, vec: &mut Vec<u8>, buf: &[u8]) -> io::Result<usize> {
-    let pos: usize = (*pos_mut).try_into().map_err(|_| {
+    let pos: usize = try_into(*pos_mut).map_err(|_| {
         Error::new(ErrorKind::InvalidInput,
                     "cursor position exceeds maximum possible vector length")
     })?;