I think I finally have intellisense mainly working.

EnginePatches/EnginePatch

@@ -1,12 +1,3 @@
-diff --git a/.clangd b/.clangd
-new file mode 100644
-index 000000000000..e10607a4bc4f
---- /dev/null
-+++ b/.clangd
-@@ -0,0 +1,3 @@
-+CompileFlags:
-+  Add:
-+    - "-D__INTELLISENSE__=1"
 diff --git a/Engine/Extras/LLDBDataFormatters/UEDataFormatters_2ByteChars.py b/Engine/Extras/LLDBDataFormatters/UEDataFormatters_2ByteChars.py
 index f56f5ea9cac4..ff1c4030b38f 100644
 --- a/Engine/Extras/LLDBDataFormatters/UEDataFormatters_2ByteChars.py

build.py

@@ -238,50 +238,30 @@ def build_luprex_and_integration():
     shell(INTEGRATION, f"{UNREALENGINE}/Engine/Build/BatchFiles/{BUILD_BAT} -waitmutex IntegrationEditor {OS} DebugGame {INTEGRATION}/Integration.uproject")
 
 
-def build_intellisense_database_for_clangd(force):
+#
+# Make a compile_commands.json file.
+#
+
+def build_intellisense_database_for_clangd():
     """
     This builds compile_commands.json, which tells the intellisense system
-    based on clangd how to compile each source file.  We automatically rebuild
-    if a C++ file has been added or removed.  That probably isn't sufficient:
-    we should also rebuild if a Build.cs file has been edited.  Coming Soon.
-    Until then, if your intellisense starts acting badly, do a 'build.py all',
-    which sets the 'force' argument above to true.
-
-    Rebuilding the intellisense database touches rsp files, which
-    unfortunately, causes the entire C++ build to be restarted the next
-    time you run 'build'.  This is terrible behavior from Unreal's build
-    system.  We have a hacky workaround: we save the RSP files before
-    running the intellisense build, then we restore them afterward.  
+    based on clangd how to compile each source file.
+    This also installs a .clangd file in the UnrealEngine directory.
     """
-    Path(f"{INTEGRATION}/.vscode").mkdir(exist_ok = True)
-    Path(f"{UNREALENGINE}/.vscode").mkdir(exist_ok = True)
-    hash_file = Path(f"{INTEGRATION}/.vscode/cpp_hash")
-    new_hash = hash_json(find_cpp(f"{INTEGRATION}/Source"))
-    old_hash = read_if_exists(hash_file).strip()
-    if (new_hash != old_hash) or force:
-        hash_file.unlink(missing_ok=True)
-        create_tarfile(f"{INTEGRATION}/Intermediate", "*.rsp", f"{INTEGRATION}/rsp_files.tgz")
-        create_tarfile(f"{UNREALENGINE}/Engine", "*.rsp", f"{UNREALENGINE}/rsp_files.tgz")
-        try:
-            Path(f"{INTEGRATION}/.vscode/compile_commands.json").unlink(missing_ok=True)
-            shell(INTEGRATION, f"{UNREALENGINE}/Engine/Build/BatchFiles/{BUILD_BAT} -waitmutex IntegrationEditor {OS} DebugGame {INTEGRATION}/Integration.uproject -mode=GenerateClangDatabase -OutputDir={INTEGRATION}/.vscode")
-            shell(UNREALENGINE, f"{UNREALENGINE}/Engine/Build/BatchFiles/{BUILD_BAT} -waitmutex UnrealEditor {OS} DebugGame -mode=GenerateClangDatabase -OutputDir={UNREALENGINE}/.vscode")
-            cc1 = json.loads(Path(f"{INTEGRATION}/.vscode/compile_commands.json").read_text())
-            cc2 = json.loads(Path(f"{INTEGRATION}/luprex/build/{OS}/compile_commands.json").read_text())
-            cc3 = json.loads(Path(f"{UNREALENGINE}/.vscode/compile_commands.json").read_text())
-            cc = cc1 + cc2 + cc3
-            Path(f"{INTEGRATION}/.vscode/compile_commands.json").write_text(json.dumps(cc, indent=2))
-        except Exception as e:
-            error = e
-        else:
-            error = None
-        # finally:
-        #     tarfile.open(f"{INTEGRATION}/rsp_files.tgz").extractall(path=f"{INTEGRATION}/Intermediate")
-        #     tarfile.open(f"{UNREALENGINE}/rsp_files.tgz").extractall(path=f"{UNREALENGINE}/Engine")
-        #     Path(f"{INTEGRATION}/rsp_files.tgz").unlink()
-        #     Path(f"{UNREALENGINE}/rsp_files.tgz").unlink()
-        if error: raise error
-        hash_file.write_text(new_hash)
+    mods1 = Path(f"{INTEGRATION}/Intermediate/Build/{OS}").rglob("UnrealEditor/DebugGame/**/Module.*.o.rsp")
+    mods2 = Path(f"{UNREALENGINE}/Engine/Intermediate/Build/{OS}").rglob("UnrealEditor/Development/**/Module.*.o.rsp")
+    mods = list(mods1) + list(mods2)
+    clangs = list(Path(f"{UNREALENGINE}/Engine/Extras/ThirdPartyNotUE/SDKs").rglob("*-linux-gnu/bin/clang++"))
+    if len(clangs) != 1: sys.exit("Couldn't identify correct clang++ compiler in UnrealEngine thirdparty directory")
+    clang = str(clangs[0])
+    ccjson = json.loads(Path(f"{INTEGRATION}/luprex/build/{OS}/compile_commands.json").read_text())
+    ccdir = f"{UNREALENGINE}/Engine/Source";
+    for mod in mods:
+        rsp = str(mod)
+        cpp = rsp.removesuffix(".o.rsp")
+        args = [clang, "@"+rsp]
+        ccjson.append({ "file" : cpp, "arguments":args, "directory":ccdir })
+    Path(f"{INTEGRATION}/.vscode/compile_commands.json").write_text(json.dumps(ccjson, indent=2))
 
 
 def generate_integration_code_workspace():
@@ -320,7 +300,7 @@ store_system_config_in_globals(CONFIG)
 os.chdir(f"{INTEGRATION}/EnginePatches")
 
 if MODE == "experiment":
-    build_intellisense_database_for_clangd(True)
+    build_intellisense_database_for_clangd()
 
 if MODE == "all":
     checkout_correct_unreal_engine_branch_and_apply_patch()
@@ -333,7 +313,7 @@ if MODE == "all":
 
 if MODE in ["all", "c++"]:
     build_luprex_and_integration()
-#    build_intellisense_database_for_clangd(MODE == "all")
+    build_intellisense_database_for_clangd()
 
 if MODE == "clean":
     build_clean()