Let build2cmake generate metadata.json (#328)

We were generating it from Nix first, but then we need the same logic on
the Windows side. So, instead, let `build2cmake` generate file and let
the Nix/Windows builders put it in place.

Author: danieldk

build2cmake/src/main.rs

@@ -20,6 +20,8 @@ use config::{Backend, Build, BuildCompat};
 mod fileset;
 use fileset::FileSet;
 
+mod metadata;
+
 mod version;
 
 #[derive(Parser, Debug)]

build2cmake/src/metadata.rs

@@ -0,0 +1,15 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(deny_unknown_fields, rename_all = "kebab-case")]
+pub struct Metadata {
+    python_depends: Vec<String>,
+}
+
+impl Metadata {
+    pub fn new(python_depends: impl Into<Vec<String>>) -> Self {
+        Self {
+            python_depends: python_depends.into(),
+        }
+    }
+}

build2cmake/src/templates/windows.cmake

@@ -161,6 +161,11 @@ function(add_local_install_target TARGET_NAME PACKAGE_NAME BUILD_VARIANT_NAME)
             ${PYTHON_FILES}
             ${LOCAL_INSTALL_DIR}/
 
+            # Copy metadata.json if it exists
+            COMMAND ${CMAKE_COMMAND} -E copy_if_different
+            ${CMAKE_SOURCE_DIR}/metadata.json
+            ${LOCAL_INSTALL_DIR}/
+
             COMMENT "Copying shared library and Python files to ${LOCAL_INSTALL_DIR}"
             COMMAND_EXPAND_LISTS
     )

build2cmake/src/torch/common.rs

@@ -3,6 +3,7 @@ use itertools::Itertools;
 use minijinja::{context, Environment};
 
 use crate::config::{Backend, General};
+use crate::metadata::Metadata;
 use crate::FileSet;
 
 pub fn write_pyproject_toml(
@@ -32,3 +33,18 @@ pub fn write_pyproject_toml(
 
     Ok(())
 }
+
+pub fn write_metadata(backend: Backend, general: &General, file_set: &mut FileSet) -> Result<()> {
+    let writer = file_set.entry("metadata.json");
+
+    let python_depends = general
+        .python_depends()
+        .chain(general.backend_python_depends(backend))
+        .collect::<Result<Vec<_>>>()?;
+
+    let metadata = Metadata::new(python_depends);
+
+    serde_json::to_writer(writer, &metadata)?;
+
+    Ok(())
+}

build2cmake/src/torch/cpu.rs

@@ -8,6 +8,7 @@ use super::{common::write_pyproject_toml, kernel_ops_identifier};
 use crate::{
     config::{Backend, Build, Kernel, Torch},
     fileset::FileSet,
+    torch::common::write_metadata,
     version::Version,
 };
 
@@ -52,6 +53,8 @@ pub fn write_torch_ext_cpu(
 
     write_torch_registration_macros(&mut file_set)?;
 
+    write_metadata(Backend::Cpu, &build.general, &mut file_set)?;
+
     Ok(file_set)
 }
 

build2cmake/src/torch/cuda.rs

@@ -10,6 +10,7 @@ use minijinja::{context, Environment};
 use super::common::write_pyproject_toml;
 use super::kernel_ops_identifier;
 use crate::config::{Backend, Build, Dependency, Kernel, Torch};
+use crate::torch::common::write_metadata;
 use crate::version::Version;
 use crate::FileSet;
 
@@ -65,6 +66,8 @@ pub fn write_torch_ext_cuda(
 
     write_torch_registration_macros(&mut file_set)?;
 
+    write_metadata(backend, &build.general, &mut file_set)?;
+
     Ok(file_set)
 }
 

build2cmake/src/torch/metal.rs

@@ -8,6 +8,7 @@ use super::{common::write_pyproject_toml, kernel_ops_identifier};
 use crate::{
     config::{Backend, Build, Kernel, Torch},
     fileset::FileSet,
+    torch::common::write_metadata,
     version::Version,
 };
 
@@ -54,6 +55,8 @@ pub fn write_torch_ext_metal(
 
     write_torch_registration_macros(&mut file_set)?;
 
+    write_metadata(Backend::Metal, &build.general, &mut file_set)?;
+
     Ok(file_set)
 }
 

build2cmake/src/torch/noarch.rs

@@ -7,7 +7,7 @@ use minijinja::{context, Environment};
 use crate::{
     config::{Backend, Build, General, Torch},
     fileset::FileSet,
-    torch::kernel_ops_identifier,
+    torch::{common::write_metadata, kernel_ops_identifier},
 };
 
 pub fn write_torch_ext_noarch(
@@ -30,6 +30,8 @@ pub fn write_torch_ext_noarch(
         &mut file_set,
     )?;
 
+    write_metadata(backend, &build.general, &mut file_set)?;
+
     Ok(file_set)
 }
 

build2cmake/src/torch/xpu.rs

@@ -9,6 +9,7 @@ use minijinja::{context, Environment};
 use super::common::write_pyproject_toml;
 use super::kernel_ops_identifier;
 use crate::config::{Backend, Build, Dependency, Kernel, Torch};
+use crate::torch::common::write_metadata;
 use crate::version::Version;
 use crate::FileSet;
 
@@ -53,6 +54,8 @@ pub fn write_torch_ext_xpu(
 
     write_torch_registration_macros(&mut file_set)?;
 
+    write_metadata(Backend::Xpu, &build.general, &mut file_set)?;
+
     Ok(file_set)
 }
 

lib/torch-extension/arch.nix

@@ -83,12 +83,6 @@ let
 
   moduleName = builtins.replaceStrings [ "-" ] [ "_" ] kernelName;
 
-  metadata = builtins.toJSON {
-    python-depends = pythonDeps;
-  };
-
-  metadataFile = writeText "metadata.json" metadata;
-
   # On Darwin, we need the host's xcrun for `xcrun metal` to compile Metal shaders.
   # It's not supported by the nixpkgs shim.
   xcrunHost = writeScriptBin "xcrunHost" ''
@@ -255,7 +249,7 @@ stdenv.mkDerivation (prevAttrs: {
     mkdir $out/${moduleName}
     cp ${./compat.py} $out/${moduleName}/__init__.py
 
-    cp ${metadataFile} $out/metadata.json
+    cp ../metadata.json $out/
   ''
   + (lib.optionalString (stripRPath && stdenv.hostPlatform.isLinux)) ''
     find $out/ -name '*.so' \