InsertChars with InputTextCallback resulting in assertion failure if resized.

[cajallen]

Version/Branch of Dear ImGui:

Version: 1.85
Branch: docking

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_opengl3.cpp + imgui_impl_glfw.cpp + imgui_stdlib.h

My Issue/Question:
Calling InsertChars() in a callback results in an assertion thrown.

// - To modify the text buffer in a callback, prefer using the InsertChars() / DeleteChars() function. InsertChars() will take care of calling the resize callback if necessary.

void ImGuiInputTextCallbackData::InsertChars(int pos, const char* new_text, const char* new_text_end)
{
    const bool is_resizable = (Flags & ImGuiInputTextFlags_CallbackResize) != 0;
    const int new_text_len = new_text_end ? (int)(new_text_end - new_text) : (int)strlen(new_text);
    if (new_text_len + BufTextLen >= BufSize)
    {
        if (!is_resizable)
            return;

        ImGuiContext& g = *GImGui;
        ImGuiInputTextState* edit_state = &g.InputTextState;
        IM_ASSERT(edit_state->ID != 0 && g.ActiveId == edit_state->ID);
        IM_ASSERT(Buf == edit_state->TextA.Data);
        int new_buf_size = BufTextLen + ImClamp(new_text_len * 4, 32, ImMax(256, new_text_len)) + 1;
        edit_state->TextA.reserve(new_buf_size + 1);
        Buf = edit_state->TextA.Data;
        BufSize = edit_state->BufCapacityA = new_buf_size;
    }

    if (BufTextLen != pos)
        memmove(Buf + pos + new_text_len, Buf + pos, (size_t)(BufTextLen - pos));
    memcpy(Buf + pos, new_text, (size_t)new_text_len * sizeof(char));
    Buf[BufTextLen + new_text_len] = '\0';

    if (CursorPos >= pos)
        CursorPos += new_text_len;
    SelectionStart = SelectionEnd = CursorPos;
    BufDirty = true;
    BufTextLen += new_text_len;
}

                    callback_data.Buf = callback_buf;
                    // Call user code
                    callback(&callback_data);

                    // Read back what user may have modified
                    IM_ASSERT(callback_data.Buf == callback_buf);  // Invalid to modify those fields

How is this supposed to work?
If it's valid to use InsertChars to modify text in a callback, and InsertChars sets Buf, then why is it invalid for Buf to be set in the callback?

Standalone, minimal, complete and verifiable example:

struct Console {
        bool input_reset;
	vector<string> input_history;
	vector<string>::iterator input_history_cursor;

	Console() {
		input_history = {"testing an input longer than 16 characters"};
		input_history_cursor = input_history.end();
	}
};

int console_input_callback(ImGuiInputTextCallbackData* data) {
	if (data->EventFlag == ImGuiInputTextFlags_CallbackHistory) {
		if (data->EventKey == ImGuiKey_UpArrow) {
			if (console.input_history_cursor == console.input_history.begin())
				console.input_history_cursor = console.input_history.end();
			else
				console.input_history_cursor--;

			data->DeleteChars(0, data->BufTextLen);

			if (console.input_history_cursor != console.input_history.end()) {
				data->InsertChars(0, console.input_history_cursor->c_str());
				data->SelectAll();
			}
		}
	} else if (data->EventFlag == ImGuiInputTextFlags_CallbackAlways) {
		if (console.input_reset) {
			data->DeleteChars(0, data->BufTextLen);
			console.input_reset = false;
		}
	}
}

void show_console(bool* open) {
	if (ImGui::Begin("Console", open)) {
		ImGui::SetNextItemWidth(ImGui::GetContentRegionAvail().x);
		static string console_input;
		auto flags = ImGuiInputTextFlags_EnterReturnsTrue | ImGuiInputTextFlags_CallbackHistory;
		if (ImGui::InputText("##ConsoleInput", &console_input, flags, console_input_callback)) {
			console.input_history.push_back(console_input);
	                console.input_history_cursor = console.input_history.end();
	                console.input_reset = true;
			ImGui::SetActiveID(ImGui::GetID("##ConsoleInput"), ImGui::GetCurrentWindow());
		}
	}
	ImGui::End();
}

This example might not show up in the Console demo, because as I understand, Buf is only resized when inputs are typed, so to set the contents to something you've previously entered isn't going to resize.

[ocornut]

Version: 1.85

Seems like a regression added last week by 5ac25e7, and afaik the code you quoted is not from 1.85 but from a more recent version. Can you confirm? I'll push a fix for current version.

[ocornut]

Fix should be eea8361

[cajallen]

Version: 1.85

Seems like a regression added last week by 5ac25e7, and afaik the code you quoted is not from 1.85 but from a more recent version. Can you confirm? I'll push a fix for current version.

Yeah, my mistake, I forgot I switched when I moved to the docking branch. Thanks for the fix!