commands: Don't raise error for duplicate commands

While trying to create a test case for #131 and #132 to demonstrate that
setting the `_GO_SCRIPTS_DIR` for a plugin incorrectly may cause it to
find the wrong command scripts, the test exited with an error at some
point because of the constraint that no duplicate scripts are allowed
by `_@go.find_commands` (via `_@go.merge_scripts_into_list`).

Since plugins may contain command names that match those in other
plugins or the top-level `_GO_SCRIPTS_DIR`, and since `_GO_SEARCH_PATHS`
has the correct semantics with regard to which command should take
precedence for any given script, I realized raising an error was no
longer appropriate. Now the first command found via searching
`_GO_SEARCH_PATHS` takes precedence over duplicates in later paths.

Author: mbland

lib/internal/commands

@@ -23,9 +23,9 @@ _@go.merge_scripts_into_list() {
     rhs_name="${rhs_script##*/}"
 
     if [[ "$lhs_name" == "$rhs_name" ]]; then
-      printf "ERROR: duplicate command $lhs_name:\n\n  %s\n  %s\n" \
-        "$lhs_script" "$rhs_script" >&2
-      return 1
+      result+=("$lhs_script")
+      ((++i))
+      ((++j))
     elif [[ "$lhs_name" < "$rhs_name" ]]; then
       result+=("$lhs_script")
       ((++i))
@@ -56,10 +56,7 @@ _@go.find_commands() {
         scripts+=("$script")
       fi
     done
-
-    if ! _@go.merge_scripts_into_list "${scripts[@]#$_GO_ROOTDIR/}"; then
-      return 1
-    fi
+    _@go.merge_scripts_into_list "${scripts[@]#$_GO_ROOTDIR/}"
   done
 
   if [[ "${#__go_command_scripts[@]}" -eq '0' ]]; then

tests/commands/find.bats

@@ -94,21 +94,19 @@ assert_command_scripts_equal() {
   assert_command_scripts_equal "${__all_scripts[@]}"
 }
 
-@test "$SUITE: return error if duplicates exists" {
+@test "$SUITE: commands from earlier paths precede duplicates in later paths" {
+  # In this case, we're trying to duplicate a builtin. Since
+  # `_GO_CORE_DIR/libexec` comes first in `_GO_SEARCH_PATHS`, it takes
+  # precedence over the duplicate we add.
   local duplicate_cmd="${BUILTIN_SCRIPTS[0]##*/}"
   local __all_scripts=("${BUILTIN_SCRIPTS[@]}")
 
   add_scripts "$duplicate_cmd"
   run "$TEST_GO_SCRIPT"
-  assert_failure
-
-  assert_line_equals 0 "ERROR: duplicate command $duplicate_cmd:"
-
-  # Because the go-core.bash file is in the test's $_GO_ROOTDIR, and the test
-  # script has a different $_GO_ROOTDIR, the builtin scripts will retain their
-  # absolute path, whereas user scripts will be relative.
-  assert_line_equals 1 "  $_GO_ROOTDIR/${BUILTIN_SCRIPTS[0]}"
-  assert_line_equals 2 "  scripts/$duplicate_cmd"
+  assert_success
+  assert_line_equals 0 "LONGEST NAME LEN: ${#LONGEST_BUILTIN_NAME}"
+  assert_line_equals 1 "COMMAND_NAMES: ${__all_scripts[*]##*/}"
+  assert_command_scripts_equal "${__all_scripts[@]}"
 }
 
 @test "$SUITE: return subcommands only" {