Generate header with version #defines for LibTorch (#50073)

Summary:
Uses cmake's `configure_file()` macro to generate a new `torch/csrc/api/include/torch/version.h` header with `TORCH_VERSION_{MAJOR,MINOR,PATCH}` \#defines from an input file `torch/csrc/api/include/torch/version.h.in`.

For Bazel builds, this is accomplished with `header_template_rule()`.

For Buck builds, this is accomplished with `fb_native.genrule()`.

Fixes https://github.com/pytorch/pytorch/issues/44365

<img width="1229" alt="Screen Shot 2021-01-05 at 3 19 24 PM" src="https://user-images.githubusercontent.com/75754324/103809279-3fd80380-5027-11eb-9039-fd23922cebd5.png">

Pull Request resolved: https://github.com/pytorch/pytorch/pull/50073

Reviewed By: glaringlee

Differential Revision: D25855877

Pulled By: jbschlosser

fbshipit-source-id: 6bb792718c97e2c2dbaa74b7b7b831a4f6938e49

.gitignore

@@ -65,6 +65,7 @@ torch/csrc/autograd/generated/*
 # Listed manually because some files in this directory are not generated
 torch/testing/_internal/generated/annotated_fn_args.py
 torch/testing/_internal/data/*.pt
+torch/csrc/api/include/torch/version.h
 torch/csrc/cudnn/cuDNN.cpp
 torch/csrc/deploy/interpreter/cpython
 torch/csrc/deploy/interpreter/frozen

BUILD.bazel

@@ -1868,6 +1868,19 @@ cc_library(
 )
 
 # torch
+py_binary(
+    name = "gen_version_header",
+    srcs = ["tools/setup_helpers/gen_version_header.py"],
+)
+
+genrule(
+    name = "version_h",
+    srcs = ["torch/csrc/api/include/torch/version.h.in", "version.txt"],
+    outs = ["torch/csrc/api/include/torch/version.h"],
+    cmd = "$(location :gen_version_header) --template-path $(location torch/csrc/api/include/torch/version.h.in) --version-path $(location version.txt) --output-path $@",
+    tools = [':gen_version_header']
+)
+
 torch_cuda_headers = glob(["torch/csrc/cuda/*.h"])
 cc_library(
     name = "torch_headers",
@@ -1888,7 +1901,7 @@ cc_library(
             "torch/csrc/autograd/generated/variable_factories.h",
             "torch/csrc/autograd/generated/Functions.h",
         ] + torch_cuda_headers,
-    ) + [":cpp_generated_code"],
+    ) + [":cpp_generated_code", ":version_h"],
     includes = [
         "torch/csrc",
         "torch/csrc/api/include",

caffe2/CMakeLists.txt

@@ -388,6 +388,10 @@ if(NOT INTERN_BUILD_MOBILE OR NOT BUILD_CAFFE2_MOBILE)
     "${TOOLS_PATH}/shared/_utils_internal.py"
     COPYONLY)
 
+  # Generate header with version info
+  configure_file("${TORCH_SRC_DIR}/csrc/api/include/torch/version.h.in"
+    "${TORCH_SRC_DIR}/csrc/api/include/torch/version.h"
+    @ONLY)
 
   set(GENERATED_CXX_TORCH
     "${TORCH_SRC_DIR}/csrc/autograd/generated/Functions.cpp"

docs/cpp/source/notes/versioning.rst

@@ -0,0 +1,27 @@
+Library Versioning
+==================
+
+We provide version number macros for identifying the version of LibTorch in use.
+Example usage:
+
+.. code-block:: cpp
+
+  #include <torch/torch.h>
+  #include <iostream>
+
+  int main() {
+    std::cout << "PyTorch version: "
+      << TORCH_VERSION_MAJOR << "."
+      << TORCH_VERSION_MINOR << "."
+      << TORCH_VERSION_PATCH << std::endl;
+  }
+
+This will output something like:
+
+.. code-block:: text
+
+  PyTorch version: 1.8.0
+
+.. note::
+
+  These macros are only available in PyTorch >= 1.8.0.

tools/setup_helpers/gen_version_header.py

@@ -0,0 +1,84 @@
+# Ideally, there would be a way in Bazel to parse version.txt
+# and use the version numbers from there as substitutions for
+# an expand_template action. Since there isn't, this silly script exists.
+
+import argparse
+import os
+
+
+def parse_version(version: str) -> (int, int, int):
+    """
+    Parses a version string into (major, minor, patch) version numbers.
+
+    Args:
+      version: Full version number string, possibly including revision / commit hash.
+
+    Returns:
+      An int 3-tuple of (major, minor, patch) version numbers.
+    """
+    # Extract version number part (i.e. toss any revision / hash parts).
+    version_number_str = version
+    for i in range(len(version)):
+        c = version[i]
+        if not (c.isdigit() or c == "."):
+            version_number_str = version[:i]
+            break
+
+    return tuple([int(n) for n in version_number_str.split(".")])
+
+
+def apply_replacements(replacements, text):
+    """
+    Applies the given replacements within the text.
+
+    Args:
+      replacements (dict): Mapping of str -> str replacements.
+      text (str): Text in which to make replacements.
+
+    Returns:
+      Text with replacements applied, if any.
+    """
+    for (before, after) in replacements.items():
+        text = text.replace(before, after)
+    return text
+
+
+def main(args):
+    with open(args.version_path) as f:
+        version = f.read().strip()
+    (major, minor, patch) = parse_version(version)
+
+    replacements = {
+        "@TORCH_VERSION_MAJOR@": str(major),
+        "@TORCH_VERSION_MINOR@": str(minor),
+        "@TORCH_VERSION_PATCH@": str(patch),
+    }
+
+    # Create the output dir if it doesn't exist.
+    os.makedirs(os.path.dirname(args.output_path), exist_ok=True)
+
+    with open(args.template_path) as input:
+        with open(args.output_path, "w") as output:
+            for line in input.readlines():
+                output.write(apply_replacements(replacements, line))
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(
+        description="Generate version.h from version.h.in template",
+    )
+    parser.add_argument(
+        "--template-path",
+        required=True,
+        help="Path to the template (i.e. version.h.in)",
+    )
+    parser.add_argument(
+        "--version-path", required=True, help="Path to the file specifying the version",
+    )
+    parser.add_argument(
+        "--output-path",
+        required=True,
+        help="Output path for expanded template (i.e. version.h)",
+    )
+    args = parser.parse_args()
+    main(args)

torch/csrc/api/include/torch/all.h

@@ -16,3 +16,4 @@
 #include <torch/types.h>
 #include <torch/utils.h>
 #include <torch/autograd.h>
+#include <torch/version.h>

torch/csrc/api/include/torch/version.h.in

@@ -0,0 +1,10 @@
+#pragma once
+
+/// Indicates the major version of LibTorch.
+#define TORCH_VERSION_MAJOR @TORCH_VERSION_MAJOR@
+
+/// Indicates the minor version of LibTorch.
+#define TORCH_VERSION_MINOR @TORCH_VERSION_MINOR@
+
+/// Indicates the patch version of LibTorch.
+#define TORCH_VERSION_PATCH @TORCH_VERSION_PATCH@