Remove broken const_type_id feature

The `const_type_id` feature was planned to stabilize in Rust 1.47, but
this was reverted in: rust-lang/rust#77083

This causes errors when building `log` with the `kv_unstable` feature on
Rust 1.47 or later.  This patch removes the use of this no-longer-stable
feature in those Rust versions.

build.rs

@@ -2,19 +2,13 @@
 //! atomics and sets `cfg` flags accordingly.
 
 use std::env;
-use std::process::Command;
-use std::str::{self, FromStr};
+use std::str;
 
 #[cfg(feature = "kv_unstable")]
 #[path = "src/kv/value/internal/cast/primitive.rs"]
 mod primitive;
 
 fn main() {
-    let minor = match rustc_minor_version() {
-        Some(minor) => minor,
-        None => return,
-    };
-
     let target = match rustc_target() {
         Some(target) => target,
         None => return,
@@ -28,11 +22,6 @@ fn main() {
         println!("cargo:rustc-cfg=has_atomics");
     }
 
-    // If the Rust version is at least 1.46.0 then we can use type ids at compile time
-    if minor >= 47 {
-        println!("cargo:rustc-cfg=const_type_id");
-    }
-
     // Generate sorted type id lookup
     #[cfg(feature = "kv_unstable")]
     primitive::generate();
@@ -61,33 +50,3 @@ fn target_has_atomics(target: &str) -> bool {
 fn rustc_target() -> Option<String> {
     env::var("TARGET").ok()
 }
-
-// From the `serde` build script
-fn rustc_minor_version() -> Option<u32> {
-    let rustc = match env::var_os("RUSTC") {
-        Some(rustc) => rustc,
-        None => return None,
-    };
-
-    let output = match Command::new(rustc).arg("--version").output() {
-        Ok(output) => output,
-        Err(_) => return None,
-    };
-
-    let version = match str::from_utf8(&output.stdout) {
-        Ok(version) => version,
-        Err(_) => return None,
-    };
-
-    let mut pieces = version.split('.');
-    if pieces.next() != Some("rustc 1") {
-        return None;
-    }
-
-    let next = match pieces.next() {
-        Some(next) => next,
-        None => return None,
-    };
-
-    u32::from_str(next).ok()
-}

src/kv/value/internal/cast/primitive.rs

@@ -13,83 +13,8 @@ In the future when `min_specialization` is stabilized we could use it instead an
 the `'static` bound altogether.
 */
 
-// Use consts to match a type with a conversion fn
-#[cfg(all(srcbuild, const_type_id))]
-pub(super) fn from_any<'v, T: ?Sized + 'static>(
-    value: &'v T,
-) -> Option<crate::kv::value::internal::Primitive<'v>> {
-    use std::any::TypeId;
-
-    use crate::kv::value::internal::Primitive;
-
-    macro_rules! to_primitive {
-        ($($ty:ty : ($const_ident:ident, $option_ident:ident),)*) => {
-            trait ToPrimitive
-            where
-                Self: 'static,
-            {
-                const CALL: fn(&Self) -> Option<Primitive> = {
-                    $(
-                        const $const_ident: TypeId = TypeId::of::<$ty>();
-                        const $option_ident: TypeId = TypeId::of::<Option<$ty>>();
-                    );*
-
-                    match TypeId::of::<Self>() {
-                        $(
-                            $const_ident => |v| Some(Primitive::from(unsafe { *(v as *const Self as *const $ty) })),
-                            $option_ident => |v| Some({
-                                let v = unsafe { *(v as *const Self as *const Option<$ty>) };
-                                match v {
-                                    Some(v) => Primitive::from(v),
-                                    None => Primitive::None,
-                                }
-                            }),
-                        )*
-
-                        _ => |_| None,
-                    }
-                };
-
-                fn to_primitive(&self) -> Option<Primitive> {
-                    (Self::CALL)(self)
-                }
-            }
-
-            impl<T: ?Sized + 'static> ToPrimitive for T {}
-        }
-    }
-
-    // NOTE: The types here *must* match the ones used below when `const_type_id` is not available
-    to_primitive![
-        usize: (USIZE, OPTION_USIZE),
-        u8: (U8, OPTION_U8),
-        u16: (U16, OPTION_U16),
-        u32: (U32, OPTION_U32),
-        u64: (U64, OPTION_U64),
-
-        isize: (ISIZE, OPTION_ISIZE),
-        i8: (I8, OPTION_I8),
-        i16: (I16, OPTION_I16),
-        i32: (I32, OPTION_I32),
-        i64: (I64, OPTION_I64),
-
-        f32: (F32, OPTION_F32),
-        f64: (F64, OPTION_F64),
-
-        char: (CHAR, OPTION_CHAR),
-        bool: (BOOL, OPTION_BOOL),
-        &'static str: (STR, OPTION_STR),
-    ];
-
-    value.to_primitive()
-}
-
-#[cfg(all(not(src_build), const_type_id))]
-#[allow(dead_code)]
-pub fn generate() {}
-
 // Use a build-time generated set of type ids to match a type with a conversion fn
-#[cfg(all(srcbuild, not(const_type_id)))]
+#[cfg(srcbuild)]
 pub(super) fn from_any<'v>(
     value: &'v (dyn std::any::Any + 'static),
 ) -> Option<crate::kv::value::internal::Primitive<'v>> {
@@ -107,7 +32,7 @@ pub(super) fn from_any<'v>(
 }
 
 // When the `src_build` config is not set then we're in the build script
-#[cfg(all(not(srcbuild), not(const_type_id)))]
+#[cfg(not(srcbuild))]
 #[allow(dead_code)]
 pub fn generate() {
     use std::path::Path;