Fix Caps Word to treat mod-taps more consistently. (#17463)

* Fix Caps Word to treat mod-taps more consistently.

Previously, holding any mod-tap key while Caps Word is active stops Caps
Word, and this happens regardless of `caps_word_press_user()`. Yet for
regular mod keys, AltGr (KC_RALT) is ignored, Shift keys are passed to
`caps_word_press_user()` to determine whether to continue, and
similarly, a key `RSFT(KC_RALT)` representing Right Shift + Alt is
passed to `caps_word_press_user()` to determine whether to continue.

This commit makes held mod-tap keys consistent with regular mod keys:

* Holding a `RALT_T` mod-tap is ignored.
* When holding a shift mod-tap key, `KC_LSFT` or `KC_RSFT` is passed to
  `caps_word_press_user()` to determine whether to continue.
* When holding a Right Shift + Alt (`RSA_T`) mod-tap, `RSFT(KC_RALT)` is
  passed to `caps_word_press_user()`.

Particularly, with this fix a user may choose to continue Caps Word when
a shift mod-tap key is held by adding `KC_LSFT` and `KC_RSFT` cases in
`caps_word_press_user()`. For instance as

```
bool caps_word_press_user(uint16_t keycode) {
  switch (keycode) {
    // Keycodes that continue Caps Word, with shift applied.
    case KC_A ... KC_Z:
    case KC_MINS:
      add_weak_mods(MOD_BIT(KC_LSFT));  // Apply shift to the next key.
      return true;

    // Keycodes that continue Caps Word, without shifting.
    case KC_1 ... KC_0:
    case KC_BSPC:
    case KC_DEL:
    case KC_UNDS:
    case KC_LSFT:  // <<< Added here.
    case KC_RSFT:
      return true;

    default:
      return false;  // Deactivate Caps Word.
  }
}
```

* Fix Caps Word to treat mod-taps more consistently.

Previously, holding any mod-tap key while Caps Word is active stops Caps
Word, and this happens regardless of `caps_word_press_user()`. Yet for
regular mod keys, AltGr (KC_RALT) is ignored, Shift keys are passed to
`caps_word_press_user()` to determine whether to continue, and
similarly, a key `RSFT(KC_RALT)` representing Right Shift + Alt is
passed to `caps_word_press_user()` to determine whether to continue.

This commit makes held mod-tap keys consistent with regular mod keys:

* Holding a `RALT_T` mod-tap is ignored.
* When holding a shift mod-tap key, `KC_LSFT` or `KC_RSFT` is passed to
  `caps_word_press_user()` to determine whether to continue.
* When holding a Right Shift + Alt (`RSA_T`) mod-tap, `RSFT(KC_RALT)` is
  passed to `caps_word_press_user()`.

Particularly, with this fix a user may choose to continue Caps Word when
a shift mod-tap key is held by adding `KC_LSFT` and `KC_RSFT` cases in
`caps_word_press_user()`. For instance as

```
bool caps_word_press_user(uint16_t keycode) {
  switch (keycode) {
    // Keycodes that continue Caps Word, with shift applied.
    case KC_A ... KC_Z:
    case KC_MINS:
      add_weak_mods(MOD_BIT(KC_LSFT));  // Apply shift to the next key.
      return true;

    // Keycodes that continue Caps Word, without shifting.
    case KC_1 ... KC_0:
    case KC_BSPC:
    case KC_DEL:
    case KC_UNDS:
    case KC_LSFT:  // <<< Added here.
    case KC_RSFT:
      return true;

    default:
      return false;  // Deactivate Caps Word.
  }
}
```

* Update quantum/process_keycode/process_caps_word.c

Co-authored-by: Joel Challis <git@zvecr.com>

2 files changed, 185 insertions, 6 deletions

diff --git a/quantum/process_keycode/process_caps_word.c b/quantum/process_keycode/process_caps_word.c
index bc4369846c..1b9583196d 100644
--- a/quantum/process_keycode/process_caps_word.c
+++ b/quantum/process_keycode/process_caps_word.c
@@ -101,14 +101,34 @@ bool process_caps_word(uint16_t keycode, keyrecord_t* record) {
                 return true;
 
 #ifndef NO_ACTION_TAPPING
+            // Corresponding to mod keys above, a held mod-tap is handled as:
+            // * For shift mods, pass KC_LSFT or KC_RSFT to
+            //   caps_word_press_user() to determine whether to continue.
+            // * For Shift + AltGr (MOD_RSFT | MOD_RALT), pass RSFT(KC_RALT).
+            // * AltGr (MOD_RALT) is ignored.
+            // * Otherwise stop Caps Word.
             case QK_MOD_TAP ... QK_MOD_TAP_MAX:
-                if (record->tap.count == 0) {
-                    // Deactivate if a mod becomes active through holding
-                    // a mod-tap key.
-                    caps_word_off();
-                    return true;
+                if (record->tap.count == 0) { // Mod-tap key is held.
+                    const uint8_t mods = (keycode >> 8) & 0x1f;
+                    switch (mods) {
+                        case MOD_LSFT:
+                            keycode = KC_LSFT;
+                            break;
+                        case MOD_RSFT:
+                            keycode = KC_RSFT;
+                            break;
+                        case MOD_RSFT | MOD_RALT:
+                            keycode = RSFT(KC_RALT);
+                            break;
+                        case MOD_RALT:
+                            return true;
+                        default:
+                            caps_word_off();
+                            return true;
+                    }
+                } else {
+                    keycode &= 0xff;
                 }
-                keycode &= 0xff;
                 break;
 
 #    ifndef NO_ACTION_LAYER
diff --git a/tests/caps_word/test_caps_word.cpp b/tests/caps_word/test_caps_word.cpp
index 0af4b0175d..3f59ed3744 100644
--- a/tests/caps_word/test_caps_word.cpp
+++ b/tests/caps_word/test_caps_word.cpp
@@ -25,10 +25,47 @@ using ::testing::AnyOf;
 using ::testing::InSequence;
 using ::testing::TestParamInfo;
 
+namespace {
+
+bool press_user_default(uint16_t keycode) {
+    switch (keycode) {
+        // Keycodes that continue Caps Word, with shift applied.
+        case KC_A ... KC_Z:
+        case KC_MINS:
+            add_weak_mods(MOD_BIT(KC_LSFT)); // Apply shift to next key.
+            return true;
+
+        // Keycodes that continue Caps Word, without shifting.
+        case KC_1 ... KC_0:
+        case KC_BSPC:
+        case KC_DEL:
+        case KC_UNDS:
+            return true;
+
+        default:
+            return false; // Deactivate Caps Word.
+    }
+}
+
+uint16_t passed_keycode;
+bool     press_user_save_passed_keycode(uint16_t keycode) {
+    passed_keycode = keycode;
+    return true;
+}
+
+bool (*press_user_fun)(uint16_t) = press_user_default;
+
+extern "C" {
+bool caps_word_press_user(uint16_t keycode) {
+    return press_user_fun(keycode);
+}
+} // extern "C"
+
 class CapsWord : public TestFixture {
    public:
     void SetUp() override {
         caps_word_off();
+        press_user_fun = press_user_default;
     }
 };
 
@@ -226,6 +263,126 @@ TEST_F(CapsWord, ShiftsAltGrSymbols) {
     testing::Mock::VerifyAndClearExpectations(&driver);
 }
 
+// Tests typing "AltGr + A" using a mod-tap key.
+TEST_F(CapsWord, ShiftsModTapAltGrSymbols) {
+    TestDriver driver;
+    KeymapKey  key_a(0, 0, 0, KC_A);
+    KeymapKey  key_altgr_t(0, 1, 0, RALT_T(KC_B));
+    set_keymap({key_a, key_altgr_t});
+
+    // Allow any number of reports with no keys or only modifiers.
+    // clang-format off
+    EXPECT_CALL(driver, send_keyboard_mock(AnyOf(
+                KeyboardReport(),
+                KeyboardReport(KC_RALT),
+                KeyboardReport(KC_LSFT, KC_RALT))))
+        .Times(AnyNumber());
+    // Expect "Shift + AltGr + A".
+    EXPECT_REPORT(driver, (KC_LSFT, KC_RALT, KC_A));
+    // clang-format on
+
+    // Turn on Caps Word and type "AltGr + A".
+    caps_word_on();
+
+    key_altgr_t.press();
+    idle_for(TAPPING_TERM + 1);
+    tap_key(key_a);
+    run_one_scan_loop();
+    key_altgr_t.release();
+
+    EXPECT_TRUE(is_caps_word_on());
+    testing::Mock::VerifyAndClearExpectations(&driver);
+}
+
+struct CapsWordPressUserParams {
+    std::string name;
+    uint16_t    keycode;
+    uint16_t    delay_ms;
+    uint16_t    expected_passed_keycode;
+    bool        continues_caps_word;
+
+    static const std::string& GetName(const TestParamInfo<CapsWordPressUserParams>& info) {
+        return info.param.name;
+    }
+};
+
+class CapsWordPressUser : public ::testing::WithParamInterface<CapsWordPressUserParams>, public CapsWord {
+    void SetUp() override {
+        caps_word_on();
+        passed_keycode = KC_NO;
+        press_user_fun = press_user_save_passed_keycode;
+    }
+};
+
+// Tests keycodes passed to caps_word_press_user() function for various keys.
+TEST_P(CapsWordPressUser, KeyCode) {
+    TestDriver driver;
+    KeymapKey  key(0, 0, 0, GetParam().keycode);
+    set_keymap({key});
+
+    EXPECT_ANY_REPORT(driver).Times(AnyNumber());
+    tap_key(key, GetParam().delay_ms);
+
+    EXPECT_EQ(passed_keycode, GetParam().expected_passed_keycode);
+    EXPECT_EQ(is_caps_word_on(), GetParam().continues_caps_word);
+    clear_oneshot_mods();
+    testing::Mock::VerifyAndClearExpectations(&driver);
+}
+
+const uint16_t LT_1_KC_A = LT(1, KC_A);
+// clang-format off
+INSTANTIATE_TEST_CASE_P(
+    PressUser,
+    CapsWordPressUser,
+    ::testing::Values(
+        CapsWordPressUserParams{
+            "KC_A", KC_A, 1, KC_A, true},
+        CapsWordPressUserParams{
+            "KC_HASH", KC_HASH, 1, KC_HASH, true},
+        CapsWordPressUserParams{
+            "KC_LSFT", KC_LSFT, 1, KC_LSFT, true},
+        CapsWordPressUserParams{
+            "KC_RSFT", KC_RSFT, 1, KC_RSFT, true},
+        CapsWordPressUserParams{
+            "LSFT_T_tapped", LSFT_T(KC_A), 1, KC_A, true},
+        CapsWordPressUserParams{
+            "LSFT_T_held", LSFT_T(KC_A), TAPPING_TERM + 1, KC_LSFT, true},
+        CapsWordPressUserParams{
+            "RSFT_T_held", RSFT_T(KC_A), TAPPING_TERM + 1, KC_RSFT, true},
+        CapsWordPressUserParams{
+            "RSA_T_held", RSA_T(KC_A), TAPPING_TERM + 1, RSFT(KC_RALT), true},
+        // Holding a mod-tap other than Shift or AltGr stops Caps Word.
+        CapsWordPressUserParams{
+            "LCTL_T_held", LCTL_T(KC_A), TAPPING_TERM + 1, KC_NO, false},
+        CapsWordPressUserParams{
+            "LALT_T_held", LALT_T(KC_A), TAPPING_TERM + 1, KC_NO, false},
+        CapsWordPressUserParams{
+            "LGUI_T_held", LGUI_T(KC_A), TAPPING_TERM + 1, KC_NO, false},
+        // Layer keys are ignored and continue Caps Word.
+        CapsWordPressUserParams{
+            "MO", MO(1), 1, KC_NO, true},
+        CapsWordPressUserParams{
+            "TO", TO(1), 1, KC_NO, true},
+        CapsWordPressUserParams{
+            "TG", TG(1), 1, KC_NO, true},
+        CapsWordPressUserParams{
+            "TT", TT(1), 1, KC_NO, true},
+        CapsWordPressUserParams{
+            "OSL", OSL(1), 1, KC_NO, true},
+        CapsWordPressUserParams{
+            "LT_held", LT_1_KC_A, TAPPING_TERM + 1, KC_NO, true},
+        // AltGr keys are ignored and continue Caps Word.
+        CapsWordPressUserParams{
+            "KC_RALT", KC_RALT, 1, KC_NO, true},
+        CapsWordPressUserParams{
+            "OSM_MOD_RALT", OSM(MOD_RALT), 1, KC_NO, true},
+        CapsWordPressUserParams{
+            "RALT_T_held", RALT_T(KC_A), TAPPING_TERM + 1, KC_NO, true}
+        ),
+    CapsWordPressUserParams::GetName
+    );
+// clang-format on
+
 struct CapsWordBothShiftsParams {
     std::string name;
     uint16_t    left_shift_keycode;
@@ -435,3 +592,5 @@ INSTANTIATE_TEST_CASE_P(
     CapsWordDoubleTapShiftParams::GetName
     );
 // clang-format on
+
+} // namespace