compose_validate: Fix buggy separated handling of empty compose box.

When I adjusted 4fbf91c135 to no longer
do a full re-validation on every character typed, that unmasked bugs
in how the compose_setup handler code and compose_validate split
responsibility for validating 0-length messages.

The user-facing result was the send button not enabling properly when
starting to type.

Fix this by moving the 0-length message validation into
compose_validate, where we already handle issues of too-long messages,
sharing the same basic logic for determining when to do a full
validate() call.

A benefit of this reworking is now all of the logic for handling the
`invalid` class is in one place in validate, rather than split with
the compose_setup module.

web/src/compose_setup.js

@@ -77,9 +77,7 @@ export function initialize() {
         }
         compose_validate.warn_if_topic_resolved(false);
         const compose_text_length = compose_validate.check_overflow_text($("#send_message_form"));
-        if (compose_text_length !== 0 && $("textarea#compose-textarea").hasClass("invalid")) {
-            $("textarea#compose-textarea").toggleClass("invalid", false);
-        }
+
         // Change compose close button tooltip as per condition.
         // We save compose text in draft only if its length is > 2.
         if (compose_text_length > 2) {

web/src/compose_validate.ts

@@ -893,6 +893,7 @@ export function check_overflow_text($container: JQuery): number {
     const $indicator = $container.find(".message-limit-indicator");
     const is_edit_container = $textarea.closest(".message_row").length > 0;
 
+    const old_no_message_content = no_message_content;
     const old_message_too_long = message_too_long;
 
     if (text.length > max_length) {
@@ -936,13 +937,21 @@ export function check_overflow_text($container: JQuery): number {
             set_message_too_long_for_compose(false);
         }
     }
-    if (!is_edit_container && message_too_long !== old_message_too_long) {
-        // If this keystroke changed the truth status for whether
-        // we're too long, then we need to refresh the send button
-        // status. This is expensive, but naturally debounced by the
-        // fact that crossing the MAX_MESSAGE_LENGTH threshold is
-        // rare.
-        validate_and_update_send_button_status();
+
+    if (!is_edit_container) {
+        // Update the state for whether the message is empty.
+        set_no_message_content(text.length === 0);
+        if (
+            message_too_long !== old_message_too_long ||
+            old_no_message_content !== no_message_content
+        ) {
+            // If this keystroke changed the truth status for whether
+            // the message is empty or too long, then we need to
+            // refresh the send button status from scratch. This is
+            // expensive, but naturally debounced by the fact this
+            // changes rarely.
+            validate_and_update_send_button_status();
+        }
     }
     return text.length;
 }
@@ -1022,10 +1031,15 @@ export let validate = (scheduling_message: boolean, show_banner = true): boolean
     set_no_message_content(no_message_content);
     if (no_message_content) {
         if (show_banner) {
+            // If you tried actually sending a message with empty
+            // compose, flash the textarea as invalid.
             $("textarea#compose-textarea").toggleClass("invalid", true);
             $("textarea#compose-textarea").trigger("focus");
         }
         return false;
+    } else if ($("textarea#compose-textarea").hasClass("invalid")) {
+        // Hide the invalid indicator now that it's non-empty.
+        $("textarea#compose-textarea").toggleClass("invalid", false);
     }
 
     if ($("#zephyr-mirror-error").is(":visible")) {

web/tests/compose_actions.test.cjs

@@ -314,6 +314,9 @@ test("respond_to_message", ({override, override_rewire, mock_template}) => {
     override_private_message_recipient({override});
     mock_template("inline_decorated_stream_name.hbs", false, noop);
 
+    override(realm, "realm_direct_message_permission_group", nobody.id);
+    override(realm, "realm_direct_message_initiator_group", everyone.id);
+
     // Test direct message
     const person = {
         user_id: 22,

web/tests/compose_validate.test.cjs

@@ -279,6 +279,8 @@ test_ui("validate", ({mock_template, override}) => {
     assert.ok(compose_validate.validate());
 
     let zephyr_error_rendered = false;
+    // For this first block, we should fail due to empty compose.
+    let expected_invalid_state = true;
     mock_template("compose_banner/compose_banner.hbs", false, (data) => {
         if (data.classname === compose_banner.CLASSNAMES.zephyr_not_running) {
             assert.equal(
@@ -296,14 +298,16 @@ test_ui("validate", ({mock_template, override}) => {
     compose_state.private_message_recipient("welcome-bot@example.com");
     $("textarea#compose-textarea").toggleClass = (classname, value) => {
         assert.equal(classname, "invalid");
-        assert.equal(value, true);
+        assert.equal(value, expected_invalid_state);
     };
     assert.ok(!compose_validate.validate());
     assert.ok(!$("#compose-send-button .loader").visible());
     assert.equal($("#compose-send-button").prop("disabled"), false);
     compose_validate.validate();
 
+    // Now add content to compose, and expect to see the banner.
     add_content_to_compose_box();
+    expected_invalid_state = false;
     let zephyr_checked = false;
     $("#zephyr-mirror-error").is = (arg) => {
         assert.equal(arg, ":visible");