Share flag consumption between parsing and completion

completion_test.go

@@ -79,3 +79,40 @@ func TestCompletionChoicesDoNotRestrictExecution(t *testing.T) {
 		t.Fatalf("outcome=%#v input=%#v", outcome, received)
 	}
 }
+
+func TestCompletionConsumesFlagGrammarAndKeepsPendingValues(t *testing.T) {
+	flags := []commandmeta.Flag{{Name: "verbose", Short: "v", Boolean: true}, {Name: "choice", Short: "c", Completion: commandmeta.CompletionHint{Kind: commandmeta.CompletionChoices}}}
+	lookup := commandmeta.NewFlagLookup(flags, []commandmeta.FlagAlias{{Source: "-x", Target: "--choice"}})
+	for _, tc := range []struct {
+		name             string
+		tokens           []string
+		pending, operand string
+		invalid          bool
+	}{
+		{name: "cluster attached empty", tokens: []string{"-vc="}, operand: ""},
+		{name: "option-looking value", tokens: []string{"-vx", "--other"}, operand: ""},
+		{name: "pending", tokens: []string{"-vx"}, pending: "choice"},
+		{name: "unknown cluster", tokens: []string{"-vz"}, invalid: true},
+		{name: "terminator", tokens: []string{"--", "--choice"}, operand: "--choice"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			state := walkCompletionFlags(tc.tokens, lookup)
+			if state.invalid != tc.invalid {
+				t.Fatalf("state=%#v", state)
+			}
+			if tc.pending != "" && (state.pending == nil || state.pending.Name != tc.pending) {
+				t.Fatalf("pending=%#v", state.pending)
+			}
+			if tc.pending == "" && state.pending != nil {
+				t.Fatalf("unexpected pending=%#v", state.pending)
+			}
+			if tc.operand != "" && (len(state.operands) != 1 || state.operands[0] != tc.operand) {
+				t.Fatalf("operands=%v", state.operands)
+			}
+		})
+	}
+	target := completionOptionTarget("-vc=", flags, lookup, nil)
+	if target.kind != completionTargetValue || target.prefix != "-vc=" || target.valuePrefix != "" {
+		t.Fatalf("partial target = %#v", target)
+	}
+}