Blame NMODL for lines it's generating.

Adds

    nmodl MOD_FILE blame --line LINE

which will cause NMODL to print a backtrace every time it writes to line
`LINE`.

This is very helpful when trying to find the NMODL code responsible for
printing a (faulty) line of code.

.github/workflows/nmodl-ci.yml

@@ -127,6 +127,7 @@ jobs:
           fi
           cmake_args+=(-DCMAKE_CXX_COMPILER=${CXX} \
                        -DCMAKE_CXX_COMPILER_LAUNCHER=ccache)
+          cmake_args+=(-DNMODL_ENABLE_BACKWARD=On)
           cmake .. "${cmake_args[@]}"
         env:
           INSTALL_DIR: ${{ runner.workspace }}/install

.gitmodules

@@ -22,3 +22,6 @@
 [submodule "ext/catch2"]
 	path = ext/catch2
 	url = https://github.com/catchorg/Catch2.git
+[submodule "ext/backward"]
+	path = ext/backward
+	url = https://github.com/bombela/backward-cpp.git

CMakeLists.txt

@@ -21,6 +21,7 @@ option(NMODL_ENABLE_PYTHON_BINDINGS "Enable pybind11 based python bindings" ON)
 option(NMODL_ENABLE_TESTS "Enable build of tests" ON)
 option(NMODL_ENABLE_USECASES
        "If building tests, additionally enable build of usecase tests. Requires neuron." OFF)
+option(NMODL_ENABLE_BACKWARD "Use backward, enables blame." OFF)
 set(NMODL_EXTRA_CXX_FLAGS
     ""
     CACHE STRING "Add extra compile flags for NMODL sources")
@@ -131,6 +132,10 @@ if(NMODL_3RDPARTY_USE_SPDLOG)
 endif()
 cpp_cc_git_submodule(spdlog BUILD PACKAGE spdlog REQUIRED)
 
+if(NMODL_ENABLE_BACKWARD)
+cpp_cc_git_submodule(backward BUILD PACKAGE backward REQUIRED)
+endif()
+
 # =============================================================================
 # Format & execute ipynb notebooks in place (pip install nbconvert clean-ipynb)
 # =============================================================================

src/codegen/codegen_cpp_visitor.hpp

@@ -198,8 +198,10 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
     CodegenCppVisitor(std::string mod_filename,
                       const std::string& output_dir,
                       std::string float_type,
-                      const bool optimize_ionvar_copies)
-        : printer(std::make_unique<CodePrinter>(output_dir + "/" + mod_filename + ".cpp"))
+                      const bool optimize_ionvar_copies,
+                      size_t blame_line = 0)
+        : printer(
+              std::make_unique<CodePrinter>(output_dir + "/" + mod_filename + ".cpp", blame_line))
         , mod_filename(std::move(mod_filename))
         , float_type(std::move(float_type))
         , optimize_ionvar_copies(optimize_ionvar_copies) {}
@@ -224,8 +226,9 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
     CodegenCppVisitor(std::string mod_filename,
                       std::ostream& stream,
                       std::string float_type,
-                      const bool optimize_ionvar_copies)
-        : printer(std::make_unique<CodePrinter>(stream))
+                      const bool optimize_ionvar_copies,
+                      size_t blame_line = 0)
+        : printer(std::make_unique<CodePrinter>(stream, blame_line))
         , mod_filename(std::move(mod_filename))
         , float_type(std::move(float_type))
         , optimize_ionvar_copies(optimize_ionvar_copies) {}

src/main.cpp

@@ -159,6 +159,9 @@ int main(int argc, const char* argv[]) {
     /// floating point data type
     std::string data_type("double");
 
+    /// which line to run blame for
+    size_t blame_line = 0;
+
     // NOLINTNEXTLINE(cppcoreguidelines-avoid-magic-numbers,readability-magic-numbers)
     app.get_formatter()->column_width(40);
     app.set_help_all_flag("-H,--help-all", "Print this help message including all sub-commands");
@@ -269,6 +272,11 @@ int main(int argc, const char* argv[]) {
         optimize_ionvar_copies_codegen,
         fmt::format("Optimize copies of ion variables ({})", optimize_ionvar_copies_codegen))->ignore_case();
 
+#if NMODL_ENABLE_BACKWARD
+    auto blame_opt = app.add_subcommand("blame", "Blame NMODL code that generated some code.");
+    blame_opt->add_option("--line", blame_line, "Justify why this line was generated.");
+#endif
+
     // clang-format on
 
     CLI11_PARSE(app, argc, argv);
@@ -538,28 +546,22 @@ int main(int argc, const char* argv[]) {
         {
             if (coreneuron_code && oacc_backend) {
                 logger->info("Running OpenACC backend code generator for CoreNEURON");
-                CodegenAccVisitor visitor(modfile,
-                                          output_dir,
-                                          data_type,
-                                          optimize_ionvar_copies_codegen);
+                CodegenAccVisitor visitor(
+                    modfile, output_dir, data_type, optimize_ionvar_copies_codegen, blame_line);
                 visitor.visit_program(*ast);
             }
 
             else if (coreneuron_code && !neuron_code && cpp_backend) {
                 logger->info("Running C++ backend code generator for CoreNEURON");
-                CodegenCoreneuronCppVisitor visitor(modfile,
-                                                    output_dir,
-                                                    data_type,
-                                                    optimize_ionvar_copies_codegen);
+                CodegenCoreneuronCppVisitor visitor(
+                    modfile, output_dir, data_type, optimize_ionvar_copies_codegen, blame_line);
                 visitor.visit_program(*ast);
             }
 
             else if (neuron_code && cpp_backend) {
                 logger->info("Running C++ backend code generator for NEURON");
-                CodegenNeuronCppVisitor visitor(modfile,
-                                                output_dir,
-                                                data_type,
-                                                optimize_ionvar_copies_codegen);
+                CodegenNeuronCppVisitor visitor(
+                    modfile, output_dir, data_type, optimize_ionvar_copies_codegen, blame_line);
                 visitor.visit_program(*ast);
             }
 

src/printer/CMakeLists.txt

@@ -3,4 +3,8 @@
 # =============================================================================
 add_library(printer OBJECT code_printer.cpp json_printer.cpp nmodl_printer.cpp)
 set_property(TARGET printer PROPERTY POSITION_INDEPENDENT_CODE ON)
-target_link_libraries(printer PRIVATE util)
+
+if(NMODL_ENABLE_BACKWARD)
+target_link_libraries(printer PRIVATE util Backward::Interface)
+target_compile_definitions(printer PUBLIC NMODL_ENABLE_BACKWARD=1)
+endif()

src/printer/code_printer.cpp

@@ -8,10 +8,15 @@
 #include "printer/code_printer.hpp"
 #include "utils/string_utils.hpp"
 
+#if NMODL_ENABLE_BACKWARD
+#include <backward.hpp>
+#endif
+
 namespace nmodl {
 namespace printer {
 
-CodePrinter::CodePrinter(const std::string& filename) {
+CodePrinter::CodePrinter(const std::string& filename, size_t blame_line)
+    : blame_line(blame_line) {
     if (filename.empty()) {
         throw std::runtime_error("Empty filename for CodePrinter");
     }
@@ -88,8 +93,9 @@ void CodePrinter::add_multi_line(const std::string& text) {
 }
 
 void CodePrinter::add_newline(std::size_t n) {
-    for (std::size_t i{}; i < n; ++i) {
+    for (std::size_t i = 0; i < n; ++i) {
         *result << '\n';
+        ++current_line;
     }
 }
 
@@ -110,5 +116,21 @@ void CodePrinter::pop_block(const std::string_view& suffix, std::size_t num_newl
     add_newline(num_newlines);
 }
 
+void CodePrinter::blame() {
+#if NMODL_ENABLE_BACKWARD
+    if (current_line == blame_line) {
+        *result << std::flush;
+
+        std::cout << "\n\n== Blame =======================================================\n";
+
+        backward::StackTrace st;
+        st.load_here(32);
+        backward::Printer p;
+        p.print(st, std::cout);
+    }
+#endif
+}
+
+
 }  // namespace printer
 }  // namespace nmodl

src/printer/code_printer.hpp

@@ -44,17 +44,21 @@ class CodePrinter {
     std::ofstream ofs;
     std::streambuf* sbuf = nullptr;
     std::unique_ptr<std::ostream> result;
+    size_t current_line = 1;
+    size_t blame_line = 0;
     size_t indent_level = 0;
     const size_t NUM_SPACES = 4;
 
   public:
-    CodePrinter()
-        : result(std::make_unique<std::ostream>(std::cout.rdbuf())) {}
+    CodePrinter(size_t blame_line = 0)
+        : result(std::make_unique<std::ostream>(std::cout.rdbuf()))
+        , blame_line(blame_line) {}
 
-    CodePrinter(std::ostream& stream)
-        : result(std::make_unique<std::ostream>(stream.rdbuf())) {}
+    CodePrinter(std::ostream& stream, size_t blame_line = 0)
+        : result(std::make_unique<std::ostream>(stream.rdbuf()))
+        , blame_line(blame_line) {}
 
-    CodePrinter(const std::string& filename);
+    CodePrinter(const std::string& filename, size_t blame_line = 0);
 
     ~CodePrinter() {
         ofs.close();
@@ -74,6 +78,7 @@ class CodePrinter {
 
     template <typename... Args>
     void add_text(Args&&... args) {
+        blame();
         (operator<<(*result, args), ...);
     }
 
@@ -127,6 +132,10 @@ class CodePrinter {
     int indent_spaces() {
         return NUM_SPACES * indent_level;
     }
+
+  private:
+    /// Blame when on the requested line.
+    void blame();
 };
 
 /** @} */  // end of printer