Make NULs work for builtins (#9859)

* Make NULs work for builtins

This switches from passing a c-string to output_stream_t::append to
passing a proper string.

That means a builtin that prints a NUL no longer crashes with "thread '' panicked
at 'String contained intermediate NUL character: ".

Instead, it will actually handle the NUL, even as an argument.

That means something like

`echo foo\x00bar` will now actually print a NUL instead of truncating
after the `foo` because we passed c-strings around everywhere.

The former is *necessary* for e.g. `string`, the latter is a change
that on the whole makes dealing with NULs easier, but it is a
behavioral change.

To restore the c-string behavior we would have to truncate arguments
at NUL.

See #9739.

* Use AsRef instead of trait bound

fish-rust/src/builtins/shared.rs

@@ -1,7 +1,7 @@
 use crate::builtins::{printf, wait};
 use crate::ffi::{self, parser_t, wcstring_list_ffi_t, Repin, RustBuiltin};
 use crate::wchar::{wstr, WString, L};
-use crate::wchar_ffi::{c_str, empty_wstring, WCharFromFFI};
+use crate::wchar_ffi::{c_str, empty_wstring, ToCppWString, WCharFromFFI};
 use crate::wgetopt::{wgetopter_t, wopt, woption, woption_argument_t};
 use libc::c_int;
 use std::os::fd::RawFd;
@@ -86,9 +86,9 @@ impl output_stream_t {
         unsafe { (*self.0).pin() }
     }
 
-    /// Append a &wtr or WString.
+    /// Append a &wstr or WString.
     pub fn append<Str: AsRef<wstr>>(&mut self, s: Str) -> bool {
-        self.ffi().append1(c_str!(s))
+        self.ffi().append(&s.as_ref().into_cpp())
     }
 
     /// Append a char.

tests/checks/string.fish

@@ -955,3 +955,8 @@ string shorten -m0 foo bar asodjsaoidj
 # CHECK: foo
 # CHECK: bar
 # CHECK: asodjsaoidj
+
+echo foo\x00bar | string escape
+# CHECK: foo\x00bar
+echo foo\\x00bar | string escape
+# CHECK: foo\\x00bar