InputText: Fixed swiching from single to multi-line while preserving same ID.

docs/CHANGELOG.txt

@@ -69,6 +69,7 @@ Other Changes:
 - Checkbox: Added CheckboxFlags() helper with int* type.
 - InputText: Fixed updating cursor/selection position when a callback altered the buffer in a way
   where the byte count is unchanged but the decoded character count changes. (#3587) [@gqw]
+- InputText: Fixed swiching from single to multi-line while preserving same ID.
 - Nav: Fixed IsItemFocused() from returning false when Nav highlight is hidden because mouse has moved.
   It's essentially been always the case but it doesn't make much sense. Instead we will aim at exposing
   feedback and control of keyboard/gamepad navigation highlight and mouse hover disable flag. (#787, #2048)

imgui_widgets.cpp

@@ -3857,9 +3857,10 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
 
     float scroll_y = is_multiline ? draw_window->Scroll.y : FLT_MAX;
 
+    const bool init_changed_specs = (state != NULL && state->Stb.single_line != !is_multiline);
     const bool init_make_active = (focus_requested || user_clicked || user_scroll_finish || user_nav_input_start);
     const bool init_state = (init_make_active || user_scroll_active);
-    if (init_state && g.ActiveId != id)
+    if ((init_state && g.ActiveId != id) || init_changed_specs)
     {
         // Access state even if we don't own it yet.
         state = &g.InputTextState;
@@ -3881,7 +3882,7 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
 
         // Preserve cursor position and undo/redo stack if we come back to same widget
         // FIXME: For non-readonly widgets we might be able to require that TextAIsValid && TextA == buf ? (untested) and discard undo stack if user buffer has changed.
-        const bool recycle_state = (state->ID == id);
+        const bool recycle_state = (state->ID == id && !init_changed_specs);
         if (recycle_state)
         {
             // Recycle existing cursor/selection/undo stack but clamp position