Expose earlier rest arguments to completion callbacks.

src/cli.toit

@@ -596,6 +596,11 @@ class CompletionContext:
   /**
   A map from option name to a list of values that have been provided
     for that option so far.
+
+  Includes both named options and rest (positional) options. Rest options
+    are keyed by their name, and their value list preserves the order of
+    the positionals consumed. This lets a completion callback for a later
+    rest argument condition its output on earlier rest values.
   */
   seen-options/Map
 

src/completion_.toit

@@ -91,7 +91,11 @@ complete_ root/Command arguments/List -> CompletionResult_:
     arg/string := args-to-process[index]
 
     if past-dashdash:
-      // After --, everything is a rest argument. Track positional index.
+      // After --, everything is a rest argument. Track positional index
+      // and record the value under its owning rest option's name.
+      rest-option := rest-option-for-index_ current-command positional-index
+      if rest-option:
+        (seen-options.get rest-option.name --init=:[]).add arg
       positional-index++
       continue.repeat
 
@@ -171,7 +175,12 @@ complete_ root/Command arguments/List -> CompletionResult_:
         all-named-options.clear
         all-short-options.clear
     else:
-      // It's a positional/rest argument.
+      // It's a positional/rest argument. Record its value under its
+      // owning rest option's name so that completion callbacks can
+      // see earlier rest arguments via context.seen-options.
+      rest-option := rest-option-for-index_ current-command positional-index
+      if rest-option:
+        (seen-options.get rest-option.name --init=:[]).add arg
       positional-index++
 
   // Now determine what to complete for the last argument (the word being typed).
@@ -366,6 +375,22 @@ complete-rest_ command/Command seen-options/Map current-word/string --positional
 
   return CompletionResult_ [] --directive=DIRECTIVE-FILE-COMPLETION_
 
+/**
+Returns the rest $Option that owns the positional at the given $positional-index
+  in $command, or null if there is no such rest option.
+
+Mirrors the parser's consumption order: each non-multi rest option consumes
+  one positional slot, and a multi rest option absorbs all remaining
+  positionals.
+*/
+rest-option-for-index_ command/Command positional-index/int -> Option?:
+  skip := positional-index
+  command.rest_.do: | option/Option |
+    if option.is-multi: return option
+    if skip == 0: return option
+    skip--
+  return null
+
 /**
 Whether the given $option has meaningful completion support.
 

tests/completion_test.toit

@@ -31,6 +31,9 @@ main:
   test-rest-positional-index
   test-rest-positional-index-after-dashdash
   test-rest-multi-not-skipped
+  test-rest-dependent-completion
+  test-rest-multi-records-all
+  test-rest-after-dashdash-recorded
   test-short-option-marks-seen
   test-short-option-pending-value
   test-packed-short-options
@@ -476,6 +479,68 @@ test-rest-multi-not-skipped:
   expect (values.contains "a.txt")
   expect (values.contains "b.txt")
 
+test-rest-dependent-completion:
+  // A completion callback for a later rest argument can condition on an
+  // earlier rest argument by reading context.seen-options.
+  seen/Map? := null
+  root := cli.Command "app"
+      --rest=[
+        cli.OptionEnum "kind" ["user", "group"] --help="Resource kind.",
+        cli.Option "name" --help="Resource name."
+            --completion=:: | context/cli.CompletionContext |
+              seen = context.seen-options
+              kind := (context.seen-options.get "kind" --if-absent=: [""]).first
+              candidates := kind == "user"
+                  ? ["alice", "bob"]
+                  : ["admins", "devs"]
+              candidates.map: cli.CompletionCandidate it,
+      ]
+      --run=:: null
+
+  result := complete_ root ["user", ""]
+  values := result.candidates.map: it.value
+  expect-equals ["user"] seen["kind"]
+  expect (values.contains "alice")
+  expect (values.contains "bob")
+  expect (not (values.contains "admins"))
+
+  result = complete_ root ["group", ""]
+  values = result.candidates.map: it.value
+  expect-equals ["group"] seen["kind"]
+  expect (values.contains "admins")
+  expect (values.contains "devs")
+  expect (not (values.contains "alice"))
+
+test-rest-multi-records-all:
+  // For a multi rest option, seen-options records every value in order.
+  seen/Map? := null
+  root := cli.Command "app"
+      --rest=[
+        cli.Option "files" --multi --help="Input files."
+            --completion=:: | context/cli.CompletionContext |
+              seen = context.seen-options
+              [],
+      ]
+      --run=:: null
+  complete_ root ["a.txt", "b.txt", "c.txt", ""]
+  expect-equals ["a.txt", "b.txt", "c.txt"] seen["files"]
+
+test-rest-after-dashdash-recorded:
+  // Positionals after -- are also recorded in seen-options under the
+  // owning rest option's name.
+  seen/Map? := null
+  root := cli.Command "app"
+      --rest=[
+        cli.OptionEnum "kind" ["user", "group"] --help="Kind.",
+        cli.Option "name" --help="Name."
+            --completion=:: | context/cli.CompletionContext |
+              seen = context.seen-options
+              [],
+      ]
+      --run=:: null
+  complete_ root ["--", "user", ""]
+  expect-equals ["user"] seen["kind"]
+
 test-short-option-marks-seen:
   root := cli.Command "app"
       --options=[