Fix TODO items

Cargo.toml

@@ -15,6 +15,8 @@ tinyvec_macros = { version = "0.1", optional = true }
 serde = { version = "1.0", optional = true, default-features = false }
 # Provides derived `Arbitrary` implementations
 arbitrary = { version = "1", optional = true }
+# Detects the available `rustc` version
+rustversion = "1.0.7"
 
 [features]
 default = []
@@ -29,17 +31,20 @@ std = ["alloc"]
 # "active" portion of an `ArrayVec` or `SliceVec`.
 grab_spare_slice = []
 
-# features that require rustc 1.40
+# formerly enabled features that require rustc 1.40
 # use Vec::append if possible in TinyVec::append - 1.37
 # DoubleEndedIterator::nth_back - 1.40
+# now these are automatically enabled if the listed rustc versions are detected
 rustc_1_40 = []
 
-# features that require rustc 1.55
+# formerly enabled features that require rustc 1.55
 # use const generics to implement Array for all array lengths
+# now that is automatically enabled if rustc 1.55+ is detected
 rustc_1_55 = ["rustc_1_40"]
 
-# features that require rustc 1.57
+# formerly enabled features that require rustc 1.57
 # add try_reserve functions to types that heap allocate.
+# now that is automatically enabled if rustc 1.57+ is detected
 rustc_1_57 = ["rustc_1_55"]
 
 # allow use of nightly feature `slice_partition_dedup`,

gen-array-impls.sh

@@ -3,6 +3,7 @@
 gen_impl() {
 	local len=$1
 	cat <<-END
+		#[rustversion::before(1.55)]
 		impl<T: Default> Array for [T; $len] {
 		  type Item = T;
 		  const CAPACITY: usize = $len;
@@ -43,6 +44,7 @@ cat <<-END
 	//     ./gen-array-impls.sh > src/array/generated_impl.rs
 	// from the repo root
 
+	#[rustversion::before(1.55)]
 	use super::Array;
 
 	$(for ((i = 0; i <= 33; i++)); do gen_impl $i; done)

src-backup/arrayset.rs

@@ -14,7 +14,8 @@ use core::{
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub struct InsertError;
 
-// TODO(when std): impl std::error::Error for InsertError {}
+#[cfg(feature = "std")]
+impl std::error::Error for InsertError {}
 
 impl fmt::Display for InsertError {
   fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

src/array.rs

@@ -8,9 +8,10 @@
 ///
 /// You are generally **not** expected to need to implement this yourself. It is
 /// already implemented for all the major array lengths (`0..=32` and the powers
-/// of 2 up to 4,096), or for all array lengths with the feature `rustc_1_55`.
+/// of 2 up to 4,096), or for all array lengths in Rust versions 1.55 and newer.
 ///
-/// **Additional lengths can easily be added upon request.**
+/// **Additional lengths can easily be added upon request for Rust 1.54 and
+/// older.**
 ///
 /// ## Safety Reminder
 ///
@@ -41,8 +42,12 @@ pub trait Array {
   fn default() -> Self;
 }
 
-#[cfg(feature = "rustc_1_55")]
+// These `*_impl` modules implement `Array` for primitive arrays.
+//
+// NOTE(2022-07-09): The `#[rustversion::...]` conditional compilation
+// attributes are placed on the individual implementation blocks rather than on
+// the modules because using procedural attribute macros on non-inline modules
+// is unstable.  Even if doing so becomes stable, it would be incompatible with
+// `tinyvec`'s MSRV.
 mod const_generic_impl;
-
-#[cfg(not(feature = "rustc_1_55"))]
 mod generated_impl;

src/array/const_generic_impl.rs

@@ -1,5 +1,7 @@
+#[rustversion::since(1.55)]
 use super::Array;
 
+#[rustversion::since(1.55)]
 impl<T: Default, const N: usize> Array for [T; N] {
   type Item = T;
   const CAPACITY: usize = N;