Add backtraces for debugging.

I've directly copied the code from backward-cpp for now,
as it is also MIT licensed, and this seemed
simpler than having to futz more with CMake and/or submodules.

Dockerfile

@@ -1,6 +1,6 @@
 FROM ubuntu:22.04 as build
 
-RUN apt update && apt install -y llvm-11 clang-11 libclang-11-dev cmake
+RUN apt update && apt install -y llvm-11 clang-11 libclang-11-dev cmake libdwarf-dev
 
 WORKDIR /lsif-clang
 

README.md

@@ -30,3 +30,8 @@ See the [examples](docs/examples.md) of producing LSIF indexes for a variety of
 # Testing the output
 
 You can use the [lsif-validate](https://github.com/sourcegraph/lsif-test) tool for basic sanity checking, or [upload the index to a Sourcegraph instance](https://docs.sourcegraph.com/user/code_intelligence/lsif_quickstart) to see the hovers, definitions, and references in action.
+
+# Additional licensing notes
+
+We use the [backwards-cpp](https://github.com/bombela/backward-cpp) code
+which is [MIT licensed](https://github.com/bombela/backward-cpp/blob/master/LICENSE.txt).

clang-tools-extra/lsif-clang/CMakeLists.txt

@@ -6,6 +6,7 @@ add_executable(lsif-clang
 
 # Make other directories available to us in clang-tools-extra
 include_directories("../clangd/")
+include_directories("../../clang/include/")
 # add_subdirectory("../clangd/indexer/")
 
 
@@ -133,9 +134,34 @@ else()
   )
 endif()
 
-target_link_libraries(lsif-clang
-  stdc++
-  clangDaemonMinimal
-)
+if (UNIX AND NOT APPLE)
+  find_path(DWARF_INCLUDE_DIR dwarf.h
+    /usr/include
+    /usr/local/include
+    /usr/include/libdwarf)
+  if (NOT DWARF_INCLUDE_DIR)
+    message(FATAL_ERROR "Couldn't find libdwarf, maybe you forgot to install libdwarf-dev(el)?")
+  endif()
+  message(STATUS "Using libdwarf in: ${DWARF_INCLUDE_DIR}")
+  target_include_directories(lsif-clang PRIVATE "${DWARF_INCLUDE_DIR}")
+  # libdwarf is not available on macOS AFAIK
+  target_link_libraries(lsif-clang
+    stdc++
+    clangDaemonMinimal
+    dwarf
+    # Linking libelf and libdl explicitly seems to be necessary after linking libdwarf
+    # Otherwise, we get errors like:
+    #  /lib/aarch64-linux-gnu/libelf.so.1: error adding symbols: DSO missing from command line
+    #  /lib/aarch64-linux-gnu/libdl.so.2: error adding symbols: DSO missing from command line
+    # See also: https://stackoverflow.com/a/38375709/2682729
+    elf
+    dl
+  )
+else()
+  target_link_libraries(lsif-clang
+    stdc++
+    clangDaemonMinimal
+  )
+endif()
 
 install(TARGETS lsif-clang)

clang-tools-extra/lsif-clang/LSIFClangMain.cpp

@@ -16,6 +16,7 @@
 #include "index/Symbol.h"
 #include "index/SymbolCollector.h"
 #include "clang/Index/IndexingOptions.h"
+#include "clang/Tooling/Backward.hpp"
 #include "clang/Tooling/AllTUsExecution.h"
 #include "clang/Tooling/ArgumentsAdjusters.h"
 #include "clang/Tooling/CommonOptionsParser.h"
@@ -30,8 +31,6 @@
 #include "llvm/Support/raw_ostream.h"
 #include <system_error>
 
-#define BACKWARD_HAS_DWARF 1
-
 using namespace clang::tooling;
 using namespace llvm;
 
@@ -123,6 +122,7 @@ class IndexActionFactory : public FrontendActionFactory {
 
 int main(int argc, const char **argv) {
   // sys::PrintStackTraceOnErrorSignal(argv[0]);
+  backward::SignalHandling sh;
 
   CommonOptionsParser OptionsParser(argc, argv, LSIFClangCategory,
                                     cl::OneOrMore);