fix(ri): avoid interference on existing COMPREPLY

The current implementation of `_comp_cmd_ri__methods` prefixes $prefix
to the generated method names.  However, this prefixing also affects
the already generated completions in COMPREPLY because it first
generates the method names by appending them to COMPRELY and then
modifies all the elements of COMPREPLY.

In the current usage, it did not produce the problem because prefix is
empty when there are existing elements in COMPREPLY, but it's
accidentally.  Before refactoring the code, we want to resolve this
dependency on the subtle condition.

completions/ri

@@ -1,36 +1,39 @@
 # ri completion for Ruby documentation                     -*- shell-script -*-
 # by Ian Macdonald <ian@caliban.org>
 
-_comp_cmd_ri__methods()
+# @var[in] ri_version
+# @var[in] prefix
+# @var[in] classes
+_comp_cmd_ri__compgen_methods()
 {
-    local regex
+    local _regex
     local IFS=$' \t\n' # needed for ${classes[@]+"${classes[@]}"} in bash-5.2
 
+    local _methods
     if [[ $ri_version == integrated ]]; then
         if [[ ! $separator ]]; then
-            regex="(Instance|Class)"
+            _regex="(Instance|Class)"
         elif [[ $separator == "#" ]]; then
-            regex=Instance
+            _regex=Instance
         else
-            regex=Class
+            _regex=Class
         fi
 
-        _comp_split -la COMPREPLY \
+        _comp_split -la _methods \
             "$(ri ${classes[@]+"${classes[@]}"} 2>/dev/null | ruby -ane \
-                'if /^'"$regex"' methods:/.../^------------------|^$/ and \
+                'if /^'"$_regex"' methods:/.../^------------------|^$/ and \
             /^ / then print $_.split(/, |,$/).grep(/^[^\[]*$/).join("\n"); \
             end' 2>/dev/null | sort -u)"
     else
         # older versions of ri didn't distinguish between class/module and
         # instance methods
-        _comp_split -la COMPREPLY \
+        _comp_split -la _methods \
             "$(ruby -W0 "$ri_path" ${classes[@]+"${classes[@]}"} 2>/dev/null | ruby -ane \
                 'if /^-/.../^-/ and ! /^-/ and ! /^ +(class|module): / then \
             print $_.split(/, |,$| +/).grep(/^[^\[]*$/).join("\n"); \
             end' | sort -u)"
-    fi
-    ((${#COMPREPLY[@]})) &&
-        _comp_compgen -c "$method" -- -P "$prefix" -W '"${COMPREPLY[@]}"'
+    fi &&
+        _comp_compgen -- -P "$prefix" -W '"${_methods[@]}"'
 }
 
 # needs at least Ruby 1.8.0 in order to use -W0
@@ -87,7 +90,7 @@ _comp_cmd_ri()
         method=${cur#*"$separator"}
         classes=($class)
         prefix=$class$separator
-        _comp_cmd_ri__methods
+        _comp_compgen -c "$method" -i ri methods
         return
     fi
 
@@ -117,8 +120,7 @@ _comp_cmd_ri()
     fi
 
     # we're completing on methods
-    method=$cur
-    _comp_cmd_ri__methods
+    _comp_cmd_ri__compgen_methods
 } &&
     complete -F _comp_cmd_ri ri