[completion] Properly implement the "124 protocol" for lazy loading.

I manually tested it with osh-unit.bash and 'zz'.  This could use an
automated test.

Remove the old, broken implementation.

core/completion.py

@@ -815,9 +815,8 @@ def LastColForWord(w):
         n = len(partial_argv)
 
         # TODO: Form prefix for RootCompleter to add to user_spec candidates
-
         if n == 0:
-          # should never get this because of Lit_CompDummy?
+          # We should never get this because of Lit_CompDummy.
           raise AssertionError
         elif n == 1:
           # First
@@ -843,8 +842,28 @@ def LastColForWord(w):
     self.comp_state.current_opts = comp_opts
     self.comp_state.currently_completing = True
     try:
-      for entry in self._PostProcess(comp_opts, user_spec, comp):
-        yield entry
+      done = False
+      while not done:
+        try:
+          for entry in self._PostProcess(comp_opts, user_spec, comp):
+            yield entry
+        except _RetryCompletion as e:
+          debug_f.log('Got 124, trying again ...')
+
+          n = len(partial_argv)
+          # Get another user_spec.  The ShellFuncAction may have 'sourced' code
+          # and run 'complete' to mutate comp_lookup, and we want to get that
+          # new entry.
+          if n == 0:
+            raise AssertionError
+          elif n == 1:
+            # First
+            comp_opts, user_spec = self.comp_lookup.GetFirstSpec()
+          else:
+            comp_opts, user_spec = self.comp_lookup.GetSpecForName(
+                partial_argv[0])
+        else:
+          done = True  # exhausted candidates without getting a retry
     finally:
       self.comp_state.currently_completing = False
 
@@ -933,22 +952,10 @@ def _GetNextCompletion(self, state):
 
     assert self.comp_iter is not None, self.comp_iter
 
-    done = False
-    while not done:
-      #self.debug_f.log('comp_iter.next()')
-      try:
-        next_completion = self.comp_iter.next()
-        done = True
-      except _RetryCompletion:
-        # TODO: Is it OK to retry here?  Shouldn't we retry in
-        # RootCompleter, after we already know the words?  That seems to run
-        # into some problems with Python generators and exceptions.
-        # I kind of want the 'g.send()' pattern to "prime the generator",
-        # revealing the first exception.
-        pass
-      except StopIteration:
-        next_completion = None  # sentinel?
-        done = True
+    try:
+      next_completion = self.comp_iter.next()
+    except StopIteration:
+      next_completion = None  # signals the end
 
     return next_completion
 

testdata/completion/osh-unit.bash

@@ -114,7 +114,8 @@ complete_optdynamic() {
 }
 complete -F complete_optdynamic optdynamic
 
-complete_files() {
+files_func() { argv "$@"; }
+complete_files_func() {
   local first=$1
   local cur=$2
   local prev=$3
@@ -124,7 +125,7 @@ complete_files() {
 }
 # everything else completes files
 #complete -D -A file
-complete -F complete_files -D  # messes up trailing slashes
+complete -F complete_files_func files_func  # messes up trailing slashes
 
 # Check trailing backslashes for the 'fileuser' command
 # Hm somehow it knows to distinguish.  Gah.
@@ -178,6 +179,19 @@ complete_F_runtime_error() {
 }
 complete -F complete_F_runtime_error F_runtime_error
 
+#
+# Test out the "124" protocol for lazy loading of completions.
+#
+
+# https://www.gnu.org/software/bash/manual/html_node/Programmable-Completion.html
+_completion_loader()
+{
+  # If the file exists, we will return 124 and reload it.
+  # TODO: It would be nice to have a debug_f builtin to trace this!
+  . "testdata/completion/${1}_completion.bash" >/dev/null 2>&1 && return 124
+}
+complete -D -F _completion_loader
+
 #
 # Unit tests use this
 #

testdata/completion/zz_completion.bash

@@ -0,0 +1,7 @@
+# Testing out the "124 protocol" with a dummy 'zz' command.
+
+_zz() {
+  COMPREPLY=(z1 z2 z3)
+}
+
+complete -F _zz zz