Rollup merge of #95397 - dtolnay:disclaimer, r=m-ou-se

Link to std::io's platform-specific behavior disclaimer

This PR adds some links in standard library documentation to point to https://doc.rust-lang.org/std/io/index.html#platform-specific-behavior.

> ### Platform-specific behavior
>
> Many I/O functions throughout the standard library are documented to indicate what various library or syscalls they are delegated to. This is done to help applications both understand what’s happening under the hood as well as investigate any possibly unclear semantics. Note, however, that this is informative, not a binding contract. The implementation of many of these functions are subject to change over time and may call fewer or more syscalls/library functions.

Many of the `std::fs` APIs already link to this disclaimer when discussing system calls.

library/std/src/env.rs

@@ -25,9 +25,11 @@
 ///
 /// # Platform-specific behavior
 ///
-/// This function currently corresponds to the `getcwd` function on Unix
+/// This function [currently] corresponds to the `getcwd` function on Unix
 /// and the `GetCurrentDirectoryW` function on Windows.
 ///
+/// [currently]: crate::io#platform-specific-behavior
+///
 /// # Errors
 ///
 /// Returns an [`Err`] if the current working directory value is invalid.
@@ -56,11 +58,13 @@ pub fn current_dir() -> io::Result<PathBuf> {
 ///
 /// # Platform-specific behavior
 ///
-/// This function currently corresponds to the `chdir` function on Unix
+/// This function [currently] corresponds to the `chdir` function on Unix
 /// and the `SetCurrentDirectoryW` function on Windows.
 ///
 /// Returns an [`Err`] if the operation fails.
 ///
+/// [currently]: crate::io#platform-specific-behavior
+///
 /// # Examples
 ///
 /// ```

library/std/src/time.rs

@@ -101,7 +101,9 @@
 /// ```
 ///
 /// # Underlying System calls
-/// Currently, the following system calls are being used to get the current time using `now()`:
+///
+/// The following system calls are [currently] being used by `now()` to find out
+/// the current time:
 ///
 /// |  Platform |               System call                                            |
 /// |-----------|----------------------------------------------------------------------|
@@ -113,6 +115,7 @@
 /// | WASI      | [__wasi_clock_time_get (Monotonic Clock)]                            |
 /// | Windows   | [QueryPerformanceCounter]                                            |
 ///
+/// [currently]: crate::io#platform-specific-behavior
 /// [QueryPerformanceCounter]: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter
 /// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
@@ -203,7 +206,8 @@
 /// For example, on Windows the time is represented in 100 nanosecond intervals whereas Linux
 /// can represent nanosecond intervals.
 ///
-/// Currently, the following system calls are being used to get the current time using `now()`:
+/// The following system calls are [currently] being used by `now()` to find out
+/// the current time:
 ///
 /// |  Platform |               System call                                            |
 /// |-----------|----------------------------------------------------------------------|
@@ -215,6 +219,7 @@
 /// | WASI      | [__wasi_clock_time_get (Realtime Clock)]                             |
 /// | Windows   | [GetSystemTimePreciseAsFileTime] / [GetSystemTimeAsFileTime]         |
 ///
+/// [currently]: crate::io#platform-specific-behavior
 /// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
 /// [gettimeofday]: https://man7.org/linux/man-pages/man2/gettimeofday.2.html