Quote only unique completions, use backslashes for ambiguous ones

Commit 29dc307111 (Insert some completions with quotes instead of backslashes,
2024-04-13) breaks some workflows. Given

	touch '[test] file1'
	touch '[test] file2'
	ls tes<Tab>

we insert completions quoted, which is inconvenient when using globs.

This implicit quoting feature is somewhat minor. But quotes look nicer,
so let's try to keep them.  Either way, users can ask for it by starting a
token with «"».

Use quoting only when we insert unique completions.

Closes #11271

src/builtins/complete.rs

@@ -513,7 +513,8 @@ pub fn complete(parser: &Parser, streams: &mut IoStreams, argv: &mut [&wstr]) ->
                     next.flags,
                     faux_cmdline,
                     &mut tmp_cursor,
-                    false,
+                    /*append_only=*/ false,
+                    /*is_unique=*/ false,
                 );
 
                 // completion_apply_to_command_line will append a space unless COMPLETE_NO_SPACE

src/reader.rs

@@ -4153,6 +4153,7 @@ fn pager_selection_changed(&mut self) {
                 &self.cycle_command_line,
                 &mut cursor_pos,
                 false,
+                /*is_unique=*/ false, // don't care
             );
             // Only update if something changed, to avoid useless edits in the undo history.
             if new_cmd_line != self.command_line.text() && new_cmd_line != self.cycle_command_line {
@@ -4841,6 +4842,7 @@ fn get_autosuggestion_performer(
                 &command_line,
                 &mut would_be_cursor,
                 /*append_only=*/ true,
+                /*is_unique=*/ false,
             );
             line_at_cursor(&full_line, would_be_cursor).to_owned()
         };
@@ -6062,6 +6064,7 @@ pub fn completion_apply_to_command_line(
     command_line: &wstr,
     inout_cursor_pos: &mut usize,
     append_only: bool,
+    is_unique: bool,
 ) -> WString {
     let mut trailer = (!flags.contains(CompleteFlags::NO_SPACE)).then_some(' ');
     let do_replace_token = flags.contains(CompleteFlags::REPLACES_TOKEN);
@@ -6088,7 +6091,7 @@ pub fn completion_apply_to_command_line(
     }
 
     let mut escape_flags = EscapeFlags::empty();
-    if append_only || trailer.is_none() {
+    if append_only || !is_unique || trailer.is_none() {
         escape_flags.insert(EscapeFlags::NO_QUOTED);
     }
     if no_tilde {
@@ -6351,7 +6354,12 @@ fn try_insert(&mut self, c: Completion, tok: &wstr, token_range: Range<usize>) {
         // If this is a replacement completion, check that we know how to replace it, e.g. that
         // the token doesn't contain evil operators like {}.
         if !c.flags.contains(CompleteFlags::REPLACES_TOKEN) || reader_can_replace(tok, c.flags) {
-            self.completion_insert(&c.completion, token_range.end, c.flags);
+            self.completion_insert(
+                &c.completion,
+                token_range.end,
+                c.flags,
+                /*is_unique=*/ true,
+            );
         }
     }
 
@@ -6491,7 +6499,12 @@ fn handle_completions(&mut self, token_range: Range<usize>) -> bool {
                 if prefix_is_partial_completion {
                     flags |= CompleteFlags::NO_SPACE;
                 }
-                self.completion_insert(&common_prefix, token_range.end, flags);
+                self.completion_insert(
+                    &common_prefix,
+                    token_range.end,
+                    flags,
+                    /*is_unique=*/ false,
+                );
                 self.cycle_command_line = self.command_line.text().to_owned();
                 self.cycle_cursor_pos = self.command_line.position();
             }
@@ -6535,7 +6548,13 @@ fn handle_completions(&mut self, token_range: Range<usize>) -> bool {
     /// \param token_end the position after the token to complete
     /// \param flags A union of all flags describing the completion to insert. See the completion_t
     /// struct for more information on possible values.
-    fn completion_insert(&mut self, val: &wstr, token_end: usize, flags: CompleteFlags) {
+    fn completion_insert(
+        &mut self,
+        val: &wstr,
+        token_end: usize,
+        flags: CompleteFlags,
+        is_unique: bool,
+    ) {
         let (elt, el) = self.active_edit_line();
 
         // Move the cursor to the end of the token.
@@ -6552,6 +6571,7 @@ fn completion_insert(&mut self, val: &wstr, token_end: usize, flags: CompleteFla
             el.text(),
             &mut cursor,
             /*append_only=*/ false,
+            is_unique,
         );
         self.set_buffer_maintaining_pager(&new_command_line, cursor);
     }

src/tests/complete.rs

@@ -163,7 +163,8 @@ macro_rules! unique_completion_applies_as {
                 completions[0].flags,
                 cmdline,
                 &mut cursor,
-                false,
+                /*append_only=*/ false,
+                /*is_unique=*/ true,
             );
             assert_eq!(newcmdline, L!($applied), "apply result mismatch");
         };
@@ -232,6 +233,7 @@ macro_rules! unique_completion_applies_as {
         L!("mv debug debug"),
         &mut cursor_pos,
         true,
+        /*is_unique=*/ false,
     );
     assert_eq!(newcmdline, L!("mv debug Debug/"));
 

src/tests/reader.rs

@@ -80,6 +80,7 @@ macro_rules! validate {
                 &line,
                 &mut cursor_pos,
                 $append_only,
+                /*is_unique=*/ false,
             );
             assert_eq!(result, expected);
             assert_eq!(cursor_pos, out_cursor_pos);

tests/checks/complete.fish

@@ -10,7 +10,7 @@ complete -c complete_test_alpha3 --no-files -w 'complete_test_alpha2 extra2'
 complete -C'complete_test_alpha1 arg1 '
 # CHECK: complete_test_alpha1 arg1
 complete --escape -C'complete_test_alpha1 arg1 '
-# CHECK: 'complete_test_alpha1 arg1 '
+# CHECK: complete_test_alpha1\ arg1\{{ }}
 complete -C'complete_test_alpha2 arg2 '
 # CHECK: complete_test_alpha1 extra1 arg2
 complete -C'complete_test_alpha3 arg3 '