Hashing: handling of "###" operator to reset to seed within a string identifier doesn't include the "###" characters in the output hash anymore.

This has various simplifying properties.
Need a test engine update too.
+ Demo: removed misleading/unnecessary usage of ###.

docs/CHANGELOG.txt

@@ -41,6 +41,14 @@ HOW TO UPDATE?
 
 Breaking Changes:
 
+- Hashing: handling of "###" operator to reset to seed within a string identifier
+  doesn't include the "###" characters in the output hash anymore:
+      Before: GetID("Hello###World") == GetID("###World") != GetID("World");
+      Now:    GetID("Hello###World") == GetID("###World") == GetID("World");
+  - This has the property of facilitating concatenating and manipulating
+    identifers using "###", and will allow fixing other dangling issues.
+  - This will invalidate hashes (stored in .ini data) for Tables and Windows
+    that are using the "###" operators. (#713, #1698)
 - Fonts: Fixed handling of `ImFontConfig::FontDataOwnedByAtlas = false` which
   did erroneously make a copy of the font data, essentially defeating the purpose
   of this flag and wasting memory (undetected since July 2015 and now spotted

imgui.cpp

@@ -2368,11 +2368,8 @@ ImGuiID ImHashData(const void* data_p, size_t data_size, ImGuiID seed)
 #endif
 }
 
-// Zero-terminated string hash, with support for ### to reset back to seed value
+// Zero-terminated string hash, with support for ### to reset back to seed value.
-// We support a syntax of "label###id" where only "###id" is included in the hash, and only "label" gets displayed.
+// e.g. "label###id" outputs the same hash as "id" (and "label" is generally displayed by the UI functions)
-// Because this syntax is rarely used we are optimizing for the common case.
-// - If we reach ### in the string we discard the hash so far and reset to the seed.
-// - We don't do 'current += 2; continue;' after handling ### to keep the code smaller/faster (measured ~10% diff in Debug build)
 // FIXME-OPT: Replace with e.g. FNV1a hash? CRC32 pretty much randomly access 1KB. Need to do proper measurements.
 ImGuiID ImHashStr(const char* data_p, size_t data_size, ImGuiID seed)
 {
@@ -2384,11 +2381,16 @@ ImGuiID ImHashStr(const char* data_p, size_t data_size, ImGuiID seed)
 #endif
     if (data_size != 0)
     {
-        while (data_size-- != 0)
+        while (data_size-- > 0)
         {
             unsigned char c = *data++;
             if (c == '#' && data_size >= 2 && data[0] == '#' && data[1] == '#')
+            {
                 crc = seed;
+                data += 2;
+                data_size -= 2;
+                continue;
+            }
 #ifndef IMGUI_ENABLE_SSE4_2_CRC
             crc = (crc >> 8) ^ crc32_lut[(crc & 0xFF) ^ c];
 #else
@@ -2401,7 +2403,11 @@ ImGuiID ImHashStr(const char* data_p, size_t data_size, ImGuiID seed)
         while (unsigned char c = *data++)
         {
             if (c == '#' && data[0] == '#' && data[1] == '#')
+            {
                 crc = seed;
+                data += 2;
+                continue;
+            }
 #ifndef IMGUI_ENABLE_SSE4_2_CRC
             crc = (crc >> 8) ^ crc32_lut[(crc & 0xFF) ^ c];
 #else
@@ -2419,7 +2425,7 @@ const char* ImHashSkipUncontributingPrefix(const char* label)
     const char* result = label;
     while (unsigned char c = *label++)
         if (c == '#' && label[0] == '#' && label[1] == '#')
-            result = label - 1;
+            result = label + 2;
     return result;
 }
 

imgui.h

@@ -30,7 +30,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM >= 12345')
 #define IMGUI_VERSION       "1.92.6 WIP"
-#define IMGUI_VERSION_NUM   19254
+#define IMGUI_VERSION_NUM   19255
 #define IMGUI_HAS_TABLE             // Added BeginTable() - from IMGUI_VERSION_NUM >= 18000
 #define IMGUI_HAS_TEXTURES          // Added ImGuiBackendFlags_RendererHasTextures - from IMGUI_VERSION_NUM >= 19198
 

imgui_demo.cpp

@@ -3358,7 +3358,7 @@ static void DemoWindowWidgetsSelectionAndMultiSelect(ImGuiDemoWindowData* demo_d
                             ImGui::TableNextColumn();
                             ImGui::SetNextItemWidth(-FLT_MIN);
                             ImGui::PushStyleVar(ImGuiStyleVar_FramePadding, ImVec2(0, 0));
-                            ImGui::InputText("###NoLabel", (char*)(void*)item_category, strlen(item_category), ImGuiInputTextFlags_ReadOnly);
+                            ImGui::InputText("##NoLabel", (char*)(void*)item_category, strlen(item_category), ImGuiInputTextFlags_ReadOnly);
                             ImGui::PopStyleVar();
                         }