[bash-completion] Support some gm.py completion

Support the various combinations of arch-mode-target that gm.py
understands, and also completion of cctests.

Bug: v8:11567
No-Try: true
Change-Id: I05285a93253f4225889e949890f5352bbc173c91
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2774708
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73639}

tools/bash-completion.sh

@@ -118,3 +118,21 @@ _maybe_setup_gdb_completions() {
 }
 _maybe_setup_gdb_completions
 unset _maybe_setup_gdb_completions
+
+_get_gm_flags() {
+  "$v8_source/tools/dev/gm.py" --print-completions
+
+  # cctest ignore directory structure, it's always "cctest/filename".
+  find "$v8_source/test/cctest/" -type f -name 'test-*' | \
+    xargs basename -a -s ".cc" | \
+    while read -r item; do echo "cctest/$item/*"; done
+}
+
+_gm_flag() {
+  local targets=$(_get_gm_flags)
+  COMPREPLY=($(compgen -W "$targets" -- "${COMP_WORDS[COMP_CWORD]}"))
+  return 0
+}
+
+# gm might be an alias, based on https://v8.dev/docs/build-gn#gm.
+complete -F _gm_flag gm.py gm

tools/dev/gm.py

@@ -170,6 +170,17 @@ def PrintHelpAndExit():
   print(HELP)
   sys.exit(0)
 
+def PrintCompletionsAndExit():
+  for a in ARCHES:
+    print("%s" % a)
+    for m in MODES:
+      print("%s" % m)
+      print("%s.%s" % (a, m))
+      for t in TARGETS:
+        print("%s" % t)
+        print("%s.%s.%s" % (a, m, t))
+  sys.exit(0)
+
 def _Call(cmd, silent=False):
   if not silent: print("# %s" % cmd)
   return subprocess.call(cmd, shell=True)
@@ -377,6 +388,8 @@ class ArgumentParser(object):
   def ParseArg(self, argstring):
     if argstring in ("-h", "--help", "help"):
       PrintHelpAndExit()
+    if argstring == "--print-completions":
+      PrintCompletionsAndExit()
     arches = []
     modes = []
     targets = []