InputText: fixed an infinite loop error happening if a custom input text callback modifies/clear BufTextLen before calling InsertChars(). (#8994, #3237)

+ misc comments.

docs/CHANGELOG.txt

@@ -64,6 +64,11 @@ Other Changes:
   The grip is not visible before hovering to reduce clutter.
 - InputText: fixed single-line InputText() not applying fine character clipping
   properly (regression in 1.92.3). (#8967) [@Cyphall]
+- InputText: fixed an infinite loop error happening if a custom input text
+  callback modifies/clear BufTextLen before calling InsertChars().
+  (regression from 1.92.3). Note that this never really worked correctly, but
+  previously it would only temporary wreck cursor position, and since 1.92.3 it
+  would go in an infinite loop. (#8994, #3237)
 - Style: added ImGuiCol_UnsavedMarker, color of the unsaved document marker when
   using ImGuiWindowFlags_UnsavedDocument/ImGuiTabItemFlags_UnsavedDocument. (#8983)
 - IO: added ImGuiPlatformIO::ClearPlatformHandlers(), ClearRendererHandlers()

imgui_demo.cpp

@@ -4804,7 +4804,7 @@ static void DemoWindowLayout()
         ImGui::SameLine();
         scroll_to_off |= ImGui::Button("Scroll Offset");
 
-        bool scroll_to_pos = ImGui::DragFloat("##pos", &scroll_to_pos_px, 1.00f, -10, FLT_MAX, "X/Y = %.0f px");;
+        bool scroll_to_pos = ImGui::DragFloat("##pos", &scroll_to_pos_px, 1.00f, -10, FLT_MAX, "X/Y = %.0f px");
         ImGui::SameLine();
         scroll_to_pos |= ImGui::Button("Scroll To Pos");
         ImGui::PopItemWidth();

imgui_internal.h

@@ -2484,7 +2484,7 @@ struct ImGuiContext
     ImGuiWindow*            LogWindow;
     ImFileHandle            LogFile;                            // If != NULL log to stdout/ file
     ImGuiTextBuffer         LogBuffer;                          // Accumulation buffer when log to clipboard. This is pointer so our GImGui static constructor doesn't call heap allocators.
-    const char*             LogNextPrefix;
+    const char*             LogNextPrefix;                      // See comment in LogSetNextTextDecoration(): doesn't copy underlying data, use carefully!
     const char*             LogNextSuffix;
     float                   LogLinePosY;
     bool                    LogLineFirstItem;

imgui_widgets.cpp

@@ -3941,6 +3941,7 @@ static ImVec2 InputTextCalcTextSize(ImGuiContext* ctx, const char* text_begin, c
 {
     ImGuiContext& g = *ctx;
     ImGuiInputTextState* obj = &g.InputTextState;
+    IM_ASSERT(text_end_display >= text_begin && text_end_display <= text_end);
     return ImFontCalcTextSizeEx(g.Font, g.FontSize, FLT_MAX, obj->WrapWidth, text_begin, text_end_display, text_end, out_remaining, out_offset, flags);
 }
 
@@ -4321,11 +4322,12 @@ void ImGuiInputTextCallbackData::InsertChars(int pos, const char* new_text, cons
     memcpy(Buf + pos, new_text, (size_t)new_text_len * sizeof(char));
     Buf[BufTextLen + new_text_len] = '\0';
 
+    BufDirty = true;
+    BufTextLen += new_text_len;
     if (CursorPos >= pos)
         CursorPos += new_text_len;
+    CursorPos = ImClamp(CursorPos, 0, BufTextLen);
     SelectionStart = SelectionEnd = CursorPos;
-    BufDirty = true;
-    BufTextLen += new_text_len;
 }
 
 void ImGui::PushPasswordFont()