C/C++ language server fixes (#987)

Fixes longstanding clangd issues (wrong selectionRange, failure to take compile_commands.json into account) and enhances documentation about C/C++ support

test/solidlsp/cpp/test_cpp_basic.py

@@ -7,8 +7,8 @@ server is not available.
 """
 
 import os
+import pathlib
 import shutil
-from typing import cast
 
 import pytest
 
@@ -17,18 +17,11 @@ from solidlsp.ls_config import Language
 from solidlsp.ls_utils import SymbolUtils
 
 
-def _clangd_available() -> bool:
-    return shutil.which("clangd") is not None
-
-
 def _ccls_available() -> bool:
     return shutil.which("ccls") is not None
 
 
-# Build parametrize list based on availability
-_cpp_servers: list[Language] = []
-if _clangd_available():
-    _cpp_servers.append(Language.CPP)
+_cpp_servers: list[Language] = [Language.CPP]
 if _ccls_available():
     _cpp_servers.append(Language.CPP_CCLS)
 
@@ -70,9 +63,9 @@ class TestCppLanguageServer:
         assert add_symbol is not None, "Could not find 'add' function symbol in b.cpp"
 
         sel_start = add_symbol["selectionRange"]["start"]
-        refs = language_server.request_references(file_path, sel_start["line"], sel_start["character"] + 1)
-        ref_files = cast(list[str], [ref.get("relativePath", "") for ref in refs])
-        assert any("a.cpp" in ref_file for ref_file in ref_files), "Should find reference in a.cpp"
+        refs = language_server.request_references(file_path, sel_start["line"], sel_start["character"])
+        ref_files = [ref.get("relativePath", "") for ref in refs]
+        assert any("a.cpp" in ref_file for ref_file in ref_files), f"Should find reference in a.cpp, {refs=}"
 
         # Verify second call returns same results (stability check)
         def _ref_key(ref: dict) -> tuple:
@@ -88,5 +81,64 @@ class TestCppLanguageServer:
                 e.get("character", -1),
             )
 
-        refs2 = language_server.request_references(file_path, sel_start["line"], sel_start["character"] + 1)
+        refs2 = language_server.request_references(file_path, sel_start["line"], sel_start["character"])
         assert sorted(map(_ref_key, refs2)) == sorted(map(_ref_key, refs)), "Reference results should be stable across calls"
+
+    @pytest.mark.parametrize("language_server", _cpp_servers, indirect=True)
+    @pytest.mark.xfail(
+        strict=True,
+        reason=("Both clangd and ccls do not support cross-file references for newly created files that were never opened by the LS."),
+    )
+    def test_find_references_in_newly_written_file(self, language_server: SolidLanguageServer) -> None:
+        # Create a new file that references the 'add' function from b.cpp
+        new_file_path = os.path.join("temp_new_file.cpp")
+        new_file_abs_path = os.path.join(language_server.repository_root_path, new_file_path)
+
+        try:
+            # Write the new file with a reference to add()
+            with open(new_file_abs_path, "w", encoding="utf-8") as f:
+                f.write(
+                    """
+#include "b.hpp"
+
+int use_add() {
+    int result = add(5, 3);
+    return result;
+}
+"""
+                )
+
+            # Open the new file so clangd knows about it
+            with language_server.open_file(new_file_path):
+                # Request document symbols to ensure the file is fully loaded by clangd
+                new_file_symbols = language_server.request_document_symbols(new_file_path).get_all_symbols_and_roots()
+                assert new_file_symbols, "New file should have symbols"
+
+            # Verify the file stays in open_file_buffers after the context exits
+            uri = pathlib.Path(new_file_abs_path).as_uri()
+            assert uri in language_server.open_file_buffers, "File should remain in open_file_buffers"
+
+            # Find the 'add' symbol in b.cpp
+            b_file_path = os.path.join("b.cpp")
+            symbols = language_server.request_document_symbols(b_file_path).get_all_symbols_and_roots()
+            symbol_list = symbols[0] if symbols and isinstance(symbols[0], list) else symbols
+            add_symbol = None
+            for sym in symbol_list:
+                if sym.get("name") == "add":
+                    add_symbol = sym
+                    break
+            assert add_symbol is not None, "Could not find 'add' function symbol in b.cpp"
+
+            # Request references for 'add'
+            sel_start = add_symbol["selectionRange"]["start"]
+            refs = language_server.request_references(b_file_path, sel_start["line"], sel_start["character"])
+            ref_files = [ref.get("relativePath", "") for ref in refs]
+
+            # Should find reference in the newly written file
+            assert any(
+                "temp_new_file.cpp" in ref_file for ref_file in ref_files
+            ), f"Should find reference in newly written temp_new_file.cpp, {ref_files=}"
+        finally:
+            # Clean up the new file
+            if os.path.exists(new_file_abs_path):
+                os.remove(new_file_abs_path)