Implement 'command' to suppress function lookup.

Motivated by bash-completion, which does 'command ls'.

core/builtin.py

@@ -884,7 +884,7 @@ def _ResolveNames(names, funcs, path_val):
 
 COMMAND_SPEC = _Register('command')
 COMMAND_SPEC.ShortFlag('-v')
-COMMAND_SPEC.ShortFlag('-V')
+#COMMAND_SPEC.ShortFlag('-V')  # Another verbose mode.
 
 
 def Command(argv, funcs, path_val):
@@ -897,11 +897,10 @@ def Command(argv, funcs, path_val):
       else:
         # This is for -v, -V is more detailed.
         print(arg)
-  else:
-    util.warn('*** command without -v not implemented ***')
-    status = 1
+    return status
+
+  raise AssertionError('command without -v should have been handled earlier')
 
-  return status
 
 
 TYPE_SPEC = _Register('type')

core/cmd_exec.py

@@ -523,7 +523,11 @@ def _MakeProcess(self, node, job_state=None, disable_errexit=False):
     p = process.Process(thunk, job_state=job_state)
     return p
 
-  def _RunSimpleCommand(self, argv, fork_external, span_id):
+  def _RunSimpleCommand(self, argv, fork_external, span_id, funcs=True):
+    """
+    Args:
+      fork_external: for subshell ( ls / ) or ( command ls / )
+    """
     # This happens when you write "$@" but have no arguments.
     if not argv:
       return 0  # status 0, or skip it?
@@ -540,13 +544,25 @@ def _RunSimpleCommand(self, argv, fork_external, span_id):
       return status
 
     # Builtins like 'true' can be redefined as functions.
-    func_node = self.funcs.get(arg0)
-    if func_node is not None:
-      # NOTE: Functions could call 'exit 42' directly, etc.
-      status = self._RunFunc(func_node, argv)
-      return status
+    if funcs:
+      func_node = self.funcs.get(arg0)
+      if func_node is not None:
+        # NOTE: Functions could call 'exit 42' directly, etc.
+        status = self._RunFunc(func_node, argv)
+        return status
 
     builtin_id = builtin.Resolve(arg0)
+
+    if builtin_id == builtin_e.COMMAND:  # 'command ls' suppresses function lookup
+      n = len(argv)
+      if n == 1:
+        return 0  # 'command', like the 'if not argv' case above
+      # The 'command' builtin syntax is simple enough that this is 100%
+      # correct, not a heuristic.
+      elif n >= 2 and argv[1] != '-v':
+        return self._RunSimpleCommand(argv[1:], fork_external, span_id,
+                                      funcs=False)
+
     if builtin_id != builtin_e.NONE:
       try:
         status = self._RunBuiltin(builtin_id, argv, span_id)

spec/builtins2.test.sh

@@ -56,3 +56,42 @@ echo
 myfunc
 status=1
 ## END
+
+#### command skips function lookup
+seq() {
+  echo "$@"
+}
+command  # no-op
+seq 3
+command seq 3
+# subshell shouldn't fork another process (but we don't have a good way of
+# testing it)
+( command seq 3 )
+## STDOUT:
+3
+1
+2
+3
+1
+2
+3
+## END
+
+#### command command seq 3
+command command seq 3
+## STDOUT:
+1
+2
+3
+## END
+## N-I zsh stdout-json: ""
+## N-I zsh status: 127
+
+#### command command -v seq
+seq() {
+  echo 3
+}
+command command -v seq
+## stdout: seq
+## N-I zsh stdout-json: ""
+## N-I zsh status: 127