Migrate truncate_at_nul to common and write some tests

This encapsulates a common pattern of truncating a wstr at its first NUL
character.

fish-rust/src/builtins/shared.rs

@@ -370,14 +370,6 @@ impl Named for BuiltinData {
     }
 }
 
-/// Helper function to convert Vec<WString> to Vec<&wstr>, truncating on NUL.
-/// We truncate on NUL for backwards-compatibility reasons.
-/// This used to be passed as c-strings (`wchar_t *`),
-/// and so we act like it for now.
-pub fn truncate_at_nul(s: &wstr) -> &wstr {
-    &s[..s.chars().position(|c| c == '\x00').unwrap_or(s.len())]
-}
-
 fn builtin_lookup(name: &wstr) -> Option<&'static BuiltinData> {
     get_by_sorted_name(name, BUILTIN_DATAS)
 }

fish-rust/src/common.rs

@@ -1162,6 +1162,15 @@ pub fn str2wcstring(inp: &[u8]) -> WString {
     result
 }
 
+/// Given an input string, return a prefix of the string up to the first NUL character,
+/// or the entire string if there is no NUL character.
+pub fn truncate_at_nul(input: &wstr) -> &wstr {
+    match input.chars().position(|c| c == '\0') {
+        Some(nul_pos) => &input[..nul_pos],
+        None => input,
+    }
+}
+
 pub fn cstr2wcstring(input: &[u8]) -> WString {
     let strlen = input.iter().position(|c| *c == b'\0').unwrap();
     str2wcstring(&input[0..strlen])

fish-rust/src/exec.rs

@@ -4,12 +4,12 @@
 // performed have been massive.
 
 use crate::builtins::shared::{
-    builtin_run, truncate_at_nul, STATUS_CMD_ERROR, STATUS_CMD_OK, STATUS_CMD_UNKNOWN,
-    STATUS_NOT_EXECUTABLE, STATUS_READ_TOO_MUCH,
+    builtin_run, STATUS_CMD_ERROR, STATUS_CMD_OK, STATUS_CMD_UNKNOWN, STATUS_NOT_EXECUTABLE,
+    STATUS_READ_TOO_MUCH,
 };
 use crate::common::{
-    exit_without_destructors, scoped_push_replacer, str2wcstring, wcs2string, wcs2zstring,
-    write_loop, ScopeGuard,
+    exit_without_destructors, scoped_push_replacer, str2wcstring, truncate_at_nul, wcs2string,
+    wcs2zstring, write_loop, ScopeGuard,
 };
 use crate::env::{EnvMode, EnvStack, Environment, Statuses, READ_BYTE_LIMIT};
 use crate::env_dispatch::use_posix_spawn;

fish-rust/src/parse_execution.rs

@@ -5,13 +5,13 @@ use crate::ast::{
 };
 use crate::builtins;
 use crate::builtins::shared::{
-    builtin_exists, truncate_at_nul, BUILTIN_ERR_VARNAME, STATUS_CMD_ERROR, STATUS_CMD_OK,
-    STATUS_CMD_UNKNOWN, STATUS_EXPAND_ERROR, STATUS_ILLEGAL_CMD, STATUS_INVALID_ARGS,
-    STATUS_NOT_EXECUTABLE, STATUS_UNMATCHED_WILDCARD,
+    builtin_exists, BUILTIN_ERR_VARNAME, STATUS_CMD_ERROR, STATUS_CMD_OK, STATUS_CMD_UNKNOWN,
+    STATUS_EXPAND_ERROR, STATUS_ILLEGAL_CMD, STATUS_INVALID_ARGS, STATUS_NOT_EXECUTABLE,
+    STATUS_UNMATCHED_WILDCARD,
 };
 use crate::common::{
-    escape, scoped_push_replacer, should_suppress_stderr_for_tests, valid_var_name, ScopeGuard,
-    ScopeGuarding,
+    escape, scoped_push_replacer, should_suppress_stderr_for_tests, truncate_at_nul,
+    valid_var_name, ScopeGuard, ScopeGuarding,
 };
 use crate::complete::CompletionList;
 use crate::env::{EnvMode, EnvStackSetResult, EnvVar, EnvVarFlags, Environment, Statuses};

fish-rust/src/tests/common.rs

@@ -1,5 +1,6 @@
 use crate::common::{
-    cstr2wcstring, format_llong_safe, format_size_safe, scoped_push, ScopeGuard, ScopeGuarding,
+    cstr2wcstring, format_llong_safe, format_size_safe, scoped_push, truncate_at_nul, ScopeGuard,
+    ScopeGuarding,
 };
 use crate::wchar::prelude::*;
 
@@ -132,3 +133,10 @@ fn test_format() {
     unsafe { libc::snprintf(buff2.as_mut_ptr().cast(), 128, "%ld\0".as_ptr().cast(), q) };
     assert_eq!(cstr2wcstring(&buff1), cstr2wcstring(&buff2));
 }
+
+#[test]
+fn test_truncate_at_nul() {
+    assert_eq!(truncate_at_nul(L!("abc\0def")), L!("abc"));
+    assert_eq!(truncate_at_nul(L!("abc")), L!("abc"));
+    assert_eq!(truncate_at_nul(L!("\0abc")), L!(""));
+}