Rollup merge of #107961 - scottmcm:unify-ilog-panics, r=Mark-Simulacrum

Avoid copy-pasting the `ilog` panic string in a bunch of places

I also ended up changing the implementations to `if let` because it doesn't work to
```rust
self.checked_ilog2().unwrap_or_else(panic_for_nonpositive_argument)
```
due to the `!`.  But as a bonus that meant I could remove the `rustc_allow_const_fn_unstable` too.

Author: Dylan-DPC

library/core/src/num/int_log10.rs

@@ -138,3 +138,11 @@ pub const fn i64(val: i64) -> u32 {
 pub const fn i128(val: i128) -> u32 {
     u128(val as u128)
 }
+
+/// Instantiate this panic logic once, rather than for all the ilog methods
+/// on every single primitive type.
+#[cold]
+#[track_caller]
+pub const fn panic_for_nonpositive_argument() -> ! {
+    panic!("argument of integer logarithm must be positive")
+}

library/core/src/num/int_macros.rs

@@ -2331,14 +2331,17 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog(self, base: Self) -> u32 {
             assert!(base >= 2, "base of integer logarithm must be at least 2");
-            self.checked_ilog(base).expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog(base) {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the base 2 logarithm of the number, rounded down.
@@ -2354,13 +2357,16 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog2(self) -> u32 {
-            self.checked_ilog2().expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog2() {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the base 10 logarithm of the number, rounded down.
@@ -2376,13 +2382,16 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog10(self) -> u32 {
-            self.checked_ilog10().expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog10() {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the logarithm of the number with respect to an arbitrary base,

library/core/src/num/uint_macros.rs

@@ -705,14 +705,17 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog(self, base: Self) -> u32 {
             assert!(base >= 2, "base of integer logarithm must be at least 2");
-            self.checked_ilog(base).expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog(base) {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the base 2 logarithm of the number, rounded down.
@@ -728,13 +731,16 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog2(self) -> u32 {
-            self.checked_ilog2().expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog2() {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the base 10 logarithm of the number, rounded down.
@@ -750,13 +756,16 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog10(self) -> u32 {
-            self.checked_ilog10().expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog10() {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the logarithm of the number with respect to an arbitrary base,