Merge branch 'assert-doc' into 'master'

add documentation to the assert header

See merge request redox-os/relibc!1444

src/header/assert/cbindgen.toml

@@ -12,6 +12,8 @@ trailer = """
 #undef assert
 #endif
 
+// _Static_assert in C23 (202311L) is considered deprecated but kept for comaptibility.
+// static_assert in C23 is considered a key word.
 #if __STDC_VERSION__ >= 201112L && !defined(__cplusplus)
 #define static_assert _Static_assert
 #endif

src/header/assert/mod.rs

@@ -7,6 +7,17 @@ use crate::{
     platform::types::{c_char, c_int},
 };
 
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/assert.html>.
+///
+/// Writes information about the function that failed to `stderr` and calls
+/// `abort()`.
+///
+/// # Implementation
+/// `assert()` is defined as a C macro in cbindgen that checks for `NDEBUG`
+/// and if not found gets forwarded to this function call.
+///
+/// # Safety
+/// `func`, `file` and `cond` are guaranteed to be non-empty and valid.
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn __assert_fail(
     func: *const c_char,
@@ -14,8 +25,14 @@ pub unsafe extern "C" fn __assert_fail(
     line: c_int,
     cond: *const c_char,
 ) -> ! {
+    // SAFETY: `func` corresponds to the identifier `__func__` which is
+    // guaranteed to be non-empty and valid.
     let func = unsafe { CStr::from_ptr(func) }.to_string_lossy();
+    // SAFETY: `file` corresponds to the macro `__FILE__` which is guaranteed
+    // to be non-empty and valid.
     let file = unsafe { CStr::from_ptr(file) }.to_string_lossy();
+    // SAFETY: `cond` corresponds to the condition being asserted and is
+    // guaranteed to be non-empty and valid.
     let cond = unsafe { CStr::from_ptr(cond) }.to_string_lossy();
 
     eprintln!("{}: {}:{}: Assertion `{}` failed.", func, file, line, cond);