Isolate hack for skipping internal separator

stage_wildcards has no need for INTERNAL_SEPARATOR. Remove it already
at this stage, to avoid the need to have the workaround in the generic
decoding routine.

Unfortunately we still can't add assert!(!fish_reserved_codepoint(c));
to wcs2bytes_callback, since builtin printf still passes arbitrary
characters. We should fix that later.

Test that printf now behaves correctly for INTERNAL_SEPARATOR.
Also add a regression test for 0c9b73e317.

src/expand.rs

@@ -1394,6 +1394,8 @@ fn stage_home_and_self(
         mut input: WString,
         out: &mut CompletionReceiver,
     ) -> ExpandResult {
+        remove_internal_separator(&mut input, self.flags.contains(ExpandFlags::SKIP_WILDCARDS));
+
         expand_home_directory(&mut input, self.ctx.vars());
         if !feature_test(FeatureFlag::RemovePercentSelf) {
             expand_percent_self(&mut input);
@@ -1406,15 +1408,11 @@ fn stage_home_and_self(
 
     fn stage_wildcards(
         &mut self,
-        mut path_to_expand: WString,
+        path_to_expand: WString,
         out: &mut CompletionReceiver,
     ) -> ExpandResult {
         let mut result = ExpandResult::ok();
 
-        remove_internal_separator(
-            &mut path_to_expand,
-            self.flags.contains(ExpandFlags::SKIP_WILDCARDS),
-        );
         let has_wildcard = wildcard_has_internal(&path_to_expand); // e.g. ANY_STRING
         let for_completions = self.flags.contains(ExpandFlags::FOR_COMPLETIONS);
         let skip_wildcards = self.flags.contains(ExpandFlags::SKIP_WILDCARDS);

src/wcstringutil.rs

@@ -1,7 +1,6 @@
 //! Helper functions for working with wcstring.
 
 use crate::common::{get_ellipsis_char, get_ellipsis_str};
-use crate::expand::INTERNAL_SEPARATOR;
 use crate::fallback::{fish_wcwidth, wcscasecmp, wcscasecmp_fuzzy};
 use crate::wchar::{decode_byte_from_char, prelude::*};
 
@@ -322,11 +321,6 @@ pub fn wcs2bytes_callback(input: &wstr, mut func: impl FnMut(&[u8]) -> bool) ->
     let mut converted = [0_u8; 4];
 
     for c in input.chars() {
-        if c == INTERNAL_SEPARATOR {
-            // do nothing, this is important for ~$user handling
-            continue;
-        }
-
         let bytes = if let Some(byte) = decode_byte_from_char(c) {
             converted[0] = byte;
             &converted[..=0]

tests/checks/basic.fish

@@ -630,6 +630,9 @@ $fish -c 'echo \ufdd2"fart"'
 echo (printf '\ufdd2foo') | string escape
 # CHECK: \Xef\Xb7\X92foo
 
+echo (printf '\ufdd8foo') | string escape
+# CHECK: \Xef\Xb7\X98foo
+
 printf '%s\n' "#!/bin/sh" 'echo $0' > $tmpdir/argv0.sh
 chmod +x $tmpdir/argv0.sh
 cd $tmpdir

tests/checks/expansion.fish

@@ -350,3 +350,17 @@ echo {asdf,~}
 # CHECK: asdf /{{.*}}
 echo {~}
 # CHECK: {~}
+
+function compare
+    test $argv[1] = $argv[2]
+    or begin
+        echo unexpected expansion result:
+        echo expected: $argv[1]
+        echo actual: $argv[2]
+    end
+end
+if string match -rq -- '^[\w.-]+$' $USER
+    set -l user_home "$(eval "echo ~$USER")"
+    compare $user_home "$(echo ~$USER)"
+    compare $user_home "$(echo ~(printf %s $USER))"
+end