use_extendr.md
In rextendr: Call Rust Code from R using the 'extendr' Crate

use_extendr() sets up extendr files correctly

Code
  use_extendr()
Message
  i First time using rextendr. Upgrading automatically...
  i Setting `Config/rextendr/version` to "0.3.1"
  v Creating 'src/rust/src'.
  v Writing 'src/entrypoint.c'
  v Writing 'src/Makevars'
  v Writing 'src/Makevars.win'
  v Writing 'src/Makevars.ucrt'
  v Writing 'src/.gitignore'
  v Adding '^src/\\.cargo$' to '.Rbuildignore'
  v Writing 'src/rust/Cargo.toml'
  v Writing 'src/rust/src/lib.rs'
  v Writing 'src/testpkg-win.def'
  v Writing 'R/extendr-wrappers.R'
  v Finished configuring extendr for package testpkg.
  * Please update the system requirement in 'DESCRIPTION' file.
  * Please run `rextendr::document()` for changes to take effect.

Code
  cat_file("R", "extendr-wrappers.R")
Output
  # nolint start

  #' @docType package
  #' @usage NULL
  #' @useDynLib testpkg, .registration = TRUE
  NULL

  #' Return string `"Hello world!"` to R.
  #' @export
  hello_world <- function() .Call(wrap__hello_world)

  # nolint end

Code
  cat_file("src", "Makevars")
Output
  TARGET_DIR = ./rust/target
  LIBDIR = $(TARGET_DIR)/release
  STATLIB = $(LIBDIR)/libtestpkg.a
  PKG_LIBS = -L$(LIBDIR) -ltestpkg

  all: C_clean

  $(SHLIB): $(STATLIB)

  CARGOTMP = $(CURDIR)/.cargo

  $(STATLIB):
    # In some environments, ~/.cargo/bin might not be included in PATH, so we need
    # to set it here to ensure cargo can be invoked. It is appended to PATH and
    # therefore is only used if cargo is absent from the user's PATH.
    if [ "$(NOT_CRAN)" != "true" ]; then \
        export CARGO_HOME=$(CARGOTMP); \
    fi && \
        export PATH="$(PATH):$(HOME)/.cargo/bin" && \
        cargo build --lib --release --manifest-path=./rust/Cargo.toml --target-dir $(TARGET_DIR)
    if [ "$(NOT_CRAN)" != "true" ]; then \
        rm -Rf $(CARGOTMP) && \
        rm -Rf $(LIBDIR)/build; \
    fi

  C_clean:
    rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS)

  clean:
    rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS) rust/target

Code
  cat_file("src", "Makevars.win")
Output
  TARGET = $(subst 64,x86_64,$(subst 32,i686,$(WIN)))-pc-windows-gnu

  TARGET_DIR = ./rust/target
  LIBDIR = $(TARGET_DIR)/$(TARGET)/release
  STATLIB = $(LIBDIR)/libtestpkg.a
  PKG_LIBS = -L$(LIBDIR) -ltestpkg -lws2_32 -ladvapi32 -luserenv -lbcrypt -lntdll

  all: C_clean

  $(SHLIB): $(STATLIB)

  CARGOTMP = $(CURDIR)/.cargo

  $(STATLIB):
    mkdir -p $(TARGET_DIR)/libgcc_mock
    # `rustc` adds `-lgcc_eh` flags to the compiler, but Rtools' GCC doesn't have
    # `libgcc_eh` due to the compilation settings. So, in order to please the
    # compiler, we need to add empty `libgcc_eh` to the library search paths.
    #
    # For more details, please refer to
    # https://github.com/r-windows/rtools-packages/blob/2407b23f1e0925bbb20a4162c963600105236318/mingw-w64-gcc/PKGBUILD#L313-L316
    touch $(TARGET_DIR)/libgcc_mock/libgcc_eh.a

    # CARGO_LINKER is provided in Makevars.ucrt for R >= 4.2
    if [ "$(NOT_CRAN)" != "true" ]; then \
        export CARGO_HOME=$(CARGOTMP); \
    fi && \
        export CARGO_TARGET_X86_64_PC_WINDOWS_GNU_LINKER="$(CARGO_LINKER)" && \
        export LIBRARY_PATH="$${LIBRARY_PATH};$(CURDIR)/$(TARGET_DIR)/libgcc_mock" && \
        cargo build --target=$(TARGET) --lib --release --manifest-path=./rust/Cargo.toml --target-dir $(TARGET_DIR)
    if [ "$(NOT_CRAN)" != "true" ]; then \
        rm -Rf $(CARGOTMP) && \
        rm -Rf $(LIBDIR)/build; \
    fi

  C_clean:
    rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS)

  clean:
    rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS) $(TARGET_DIR)

Code
  cat_file("src", "Makevars.ucrt")
Output
  # Rtools42 doesn't have the linker in the location that cargo expects, so we
  # need to overwrite it via configuration.
  CARGO_LINKER = x86_64-w64-mingw32.static.posix-gcc.exe

  include Makevars.win

Code
  cat_file("src", "entrypoint.c")
Output
  // We need to forward routine registration from C to Rust
  // to avoid the linker removing the static library.

  void R_init_testpkg_extendr(void *dll);

  void R_init_testpkg(void *dll) {
      R_init_testpkg_extendr(dll);
  }

Code
  cat_file("src", "testpkg-win.def")
Output
  EXPORTS
  R_init_testpkg

Code
  cat_file("src", "rust", "Cargo.toml")
Output
  [package]
  name = 'testpkg'
  version = '0.1.0'
  edition = '2021'

  [lib]
  crate-type = [ 'staticlib' ]
  name = 'testpkg'

  [dependencies]
  extendr-api = '*'

Code
  cat_file("src", "rust", "src", "lib.rs")
Output
  use extendr_api::prelude::*;

  /// Return string `"Hello world!"` to R.
  /// @export
  #[extendr]
  fn hello_world() -> &'static str {
      "Hello world!"
  }

  // Macro to generate exports.
  // This ensures exported functions are registered with R.
  // See corresponding C code in `entrypoint.c`.
  extendr_module! {
      mod testpkg;
      fn hello_world;
  }