Rollup merge of #133701 - kornelski:c-str, r=workingjubilee

Use c"lit" for CStrings without unwrap

I've reviewed uses of `CString::new("lit")`.

Some could be changed to `c"lit"`. Some could be changed to `c"lit".to_owned()`, avoiding an `unwrap()`.

Many `CString` documentation examples could be simplified. I deliberately haven't changed all the examples to use the exact same expression, so that they can demonstrate many ways of creating `CString`s.

I've left UI tests mostly unchanged, because `c""` requires edition 2021, but most UI tests use 2015, and I didn't want to accidentally change what the tests are testing.

Author: GuillaumeGomez

tests/pass-dep/libc/libc-fs-symlink.rs

@@ -47,9 +47,8 @@ fn test_readlink() {
     assert_eq!(res, small_buf.len() as isize);
 
     // Test that we report a proper error for a missing path.
-    let bad_path = CString::new("MIRI_MISSING_FILE_NAME").unwrap();
     let res = unsafe {
-        libc::readlink(bad_path.as_ptr(), small_buf.as_mut_ptr().cast(), small_buf.len())
+        libc::readlink(c"MIRI_MISSING_FILE_NAME".as_ptr(), small_buf.as_mut_ptr().cast(), small_buf.len())
     };
     assert_eq!(res, -1);
     assert_eq!(Error::last_os_error().kind(), ErrorKind::NotFound);

tests/pass-dep/libc/libc-fs-with-isolation.rs

@@ -2,7 +2,6 @@
 //@compile-flags: -Zmiri-isolation-error=warn-nobacktrace
 //@normalize-stderr-test: "(stat(x)?)" -> "$$STAT"
 
-use std::ffi::CString;
 use std::fs;
 use std::io::{Error, ErrorKind};
 
@@ -13,10 +12,9 @@ fn main() {
     }
 
     // test `readlink`
-    let symlink_c_str = CString::new("foo.txt").unwrap();
     let mut buf = vec![0; "foo_link.txt".len() + 1];
     unsafe {
-        assert_eq!(libc::readlink(symlink_c_str.as_ptr(), buf.as_mut_ptr(), buf.len()), -1);
+        assert_eq!(libc::readlink(c"foo.txt".as_ptr(), buf.as_mut_ptr(), buf.len()), -1);
         assert_eq!(Error::last_os_error().raw_os_error(), Some(libc::EACCES));
     }
 

tests/pass-dep/libc/libc-mem.rs

@@ -55,12 +55,12 @@ fn test_memcpy() {
 }
 
 fn test_strcpy() {
-    use std::ffi::{CStr, CString};
+    use std::ffi::CStr;
 
     // case: src_size equals dest_size
     unsafe {
-        let src = CString::new("rust").unwrap();
-        let size = src.as_bytes_with_nul().len();
+        let src = c"rust";
+        let size = src.to_bytes_with_nul().len();
         let dest = libc::malloc(size);
         libc::strcpy(dest as *mut libc::c_char, src.as_ptr());
         assert_eq!(CStr::from_ptr(dest as *const libc::c_char), src.as_ref());
@@ -69,8 +69,8 @@ fn test_strcpy() {
 
     // case: src_size is less than dest_size
     unsafe {
-        let src = CString::new("rust").unwrap();
-        let size = src.as_bytes_with_nul().len();
+        let src = c"rust";
+        let size = src.to_bytes_with_nul().len();
         let dest = libc::malloc(size + 1);
         libc::strcpy(dest as *mut libc::c_char, src.as_ptr());
         assert_eq!(CStr::from_ptr(dest as *const libc::c_char), src.as_ref());