Add nFPM backend for building system packages (only the nfpm core bits)

docs/docs/using-pants/key-concepts/backends.mdx

@@ -92,6 +92,7 @@ The list of all backends (both stable and experimental) is also available via `p
 | `pants.backend.experimental.kotlin`                                | Enables core Kotlin support                                                                                                                           | [Kotlin](../../jvm/kotlin.mdx)                                                                        |
 | `pants.backend.experimental.kotlin.debug_goals`                    | Enables additional goals for introspecting Kotlin targets                                                                                             | [Kotlin](../../jvm/kotlin.mdx)                                                                        |
 | `pants.backend.experimental.kotlin.lint.ktlint`                    | Enables ktlint, an anti-bikeshedding linter with built-in formatter: [https://pinterest.github.io/ktlint/](https://pinterest.github.io/ktlint/)       | [Kotlin](../../jvm/kotlin.mdx)                                                                        |
+| `pants.backend.experimental.nfpm`                                  | Enables support for building `apk`, `archlinux`, `deb`, and `rpm` packages via [`nFPM`](https://nfpm.goreleaser.com/)                                 | [`nfpm`](../../../reference/subsystems/nfpm.mdx)                                                      |
 | `pants.backend.experimental.openapi`                               | Enables core OpenAPI support: [https://swagger.io/specification/](https://swagger.io/specification/)                                                  | [`openapi`](../../../reference/subsystems/openapi.mdx)                                                |
 | `pants.backend.experimental.openapi.codegen.java`                  | Enables generating Java from OpenAPI                                                                                                                  |                                                                                                       |
 | `pants.backend.experimental.openapi.lint.openapi_format`           | Enables openapi-format: [https://github.com/thim81/openapi-format](https://github.com/thim81/openapi-format)                                          |                                                                                                       |

docs/notes/2.23.x.md

@@ -63,6 +63,41 @@ The `output_path` field present on targets which can be packaged by `pants packa
 
 ### Backends
 
+#### NEW: nFPM
+
+A new experimental `pants.backend.experimental.nfpm` backend was added to support building system packages with [`nFPM`](https://nfpm.goreleaser.com/). nFPM describes itself as:
+
+> **nFPM is Not FPM** - a zero dependencies, simple `deb`, `rpm`, `apk`, `ipk`, and arch linux packager written in Go.
+
+This backend does not have any package types yet.
+
+To use the `nFPM` backend, enable `pants.backend.experimental.nfpm` in your `pants.toml`, and create an `nfpm_*_package` target that depends on `nfpm_content_*` targets. This backend constructs the `nfpm.yaml` file that `nFPM` relies on to build packages. All `nfpm.yaml` fields (that make sense within pants) can be configured via the `nfpm_*_package` and `nfpm_content_*` targets.
+
+This backend has extensive help documentation. Please use `pants help` to learn about the fields on these targets.
+
+Learn general info about nFPM and available targets:
+```
+$ pants help backends | grep -A6 pants.backend.experimental.nfpm
+$ pants help nfpm
+$ pants help tools | grep -A3 nfpm
+$ pants help targets | grep -A1 nfpm_
+```
+
+Learn about the nFPM package targets and their fields:
+```
+# Not available yet.
+```
+
+Learn about the nFPM package content targets and their fields:
+```
+$ pants help nfpm_content_files
+$ pants help nfpm_content_file
+$ pants help nfpm_content_dirs
+$ pants help nfpm_content_dir
+$ pants help nfpm_content_symlinks
+$ pants help nfpm_content_symlink
+```
+
 #### BUILD
 
 Support for parametrizing grouped parametrizations. (e.g. `**parametrize(resolve=parametrize("a", "b"), ...)`). This works for `___defaults__` as well, as long as it is specified per target type rather than using `all`.

src/python/pants/backend/experimental/nfpm/BUILD

@@ -0,0 +1,4 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources()

src/python/pants/backend/experimental/nfpm/register.py

@@ -0,0 +1,28 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+"""Create apk, archlinux, deb, and rpm system packages.
+
+See https://nfpm.goreleaser.com/ for details on nFPM, including these descriptions of it:
+  - nFPM is "effing simple package management"
+  - "nFPM is Not FPM--a zero dependencies, simple deb, rpm, apk, and arch linux packager written in Go."
+"""  # TODO: include ipk in this docstring once support is added.
+
+from pants.backend.nfpm.dependency_inference import rules as nfpm_dependency_inference_rules
+from pants.backend.nfpm.rules import rules as nfpm_rules
+from pants.backend.nfpm.subsystem import rules as nfpm_subsystem_rules
+from pants.backend.nfpm.target_types import target_types as nfpm_target_types
+from pants.backend.nfpm.target_types_rules import rules as nfpm_target_type_rules
+
+
+def target_types():
+    return nfpm_target_types()
+
+
+def rules():
+    return [
+        *nfpm_subsystem_rules(),
+        *nfpm_target_type_rules(),
+        *nfpm_dependency_inference_rules(),
+        *nfpm_rules(),
+    ]

src/python/pants/backend/nfpm/BUILD

@@ -0,0 +1,6 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources()
+
+python_tests(name="tests")

src/python/pants/backend/nfpm/config.py

@@ -0,0 +1,41 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import annotations
+
+from typing import TypedDict
+
+import yaml
+
+
+class OctalInt(int):
+    # noinspection PyUnusedLocal
+    @staticmethod
+    def represent_octal(dumper: yaml.representer.BaseRepresenter, data: int) -> yaml.Node:
+        # YAML 1.2 octal: 0o7777 (py: f"0o{data:o}" or f"{data:#o}" or oct(data))
+        # YAML 1.1 octal: 07777 (py: f"0{data:o}")
+        # Both octal reprs are supported by `gopkg.in/yaml.v3` which parses YAML in nFPM.
+        # See: https://github.com/go-yaml/yaml/tree/v3.0.1#compatibility
+        # PyYAML only supports reading YAML 1.1, so we use that.
+        return yaml.ScalarNode("tag:yaml.org,2002:int", f"0{data:o}")
+
+
+# This is an unfortunate import-time side effect: PyYAML does registration globally.
+yaml.SafeDumper.add_representer(OctalInt, OctalInt.represent_octal)
+
+
+class NfpmFileInfo(TypedDict, total=False):
+    # nFPM allows these to be None or missing.
+    # Each of the fields has a default, so in practice, these won't be None.
+    owner: str | None
+    group: str | None
+    mode: OctalInt | None
+    mtime: str | None
+
+
+class NfpmContent(TypedDict, total=False):
+    src: str
+    dst: str
+    type: str
+    packager: str
+    file_info: NfpmFileInfo

src/python/pants/backend/nfpm/dependency_inference.py

@@ -0,0 +1,56 @@
+# Copyright 2024 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from pants.backend.nfpm.fields.scripts import NfpmPackageScriptsField
+from pants.base.glob_match_error_behavior import GlobMatchErrorBehavior
+from pants.base.specs import FileLiteralSpec, RawSpecs
+from pants.engine.internals.specs_rules import resolve_addresses_from_raw_specs
+from pants.engine.rules import collect_rules, rule
+from pants.engine.target import FieldSet, InferDependenciesRequest, InferredDependencies
+from pants.engine.unions import UnionRule
+from pants.util.logging import LogLevel
+
+
+@dataclass(frozen=True)
+class NfpmPackageScriptsInferenceFieldSet(FieldSet):
+    required_fields = (NfpmPackageScriptsField,)
+
+    scripts: NfpmPackageScriptsField
+
+
+class InferNfpmPackageScriptsDependencies(InferDependenciesRequest):
+    infer_from = NfpmPackageScriptsInferenceFieldSet
+
+
+@rule(
+    desc=f"Infer dependencies based on nfpm `{NfpmPackageScriptsField.alias}` field.",
+    level=LogLevel.DEBUG,
+)
+async def infer_nfpm_package_scripts_dependencies(
+    request: InferNfpmPackageScriptsDependencies,
+) -> InferredDependencies:
+    scripts: NfpmPackageScriptsField = request.field_set.scripts
+    scripts_paths = tuple(scripts.normalized_value.values())
+    if not scripts_paths:
+        return InferredDependencies(())
+
+    resolved_scripts_addresses = await resolve_addresses_from_raw_specs(
+        RawSpecs(
+            file_literals=tuple(FileLiteralSpec(script_path) for script_path in scripts_paths),
+            unmatched_glob_behavior=GlobMatchErrorBehavior.error,
+            description_of_origin="nfpm package scripts field dependency inference",
+        )
+    )
+
+    return InferredDependencies(resolved_scripts_addresses)
+
+
+def rules():
+    return [
+        *collect_rules(),
+        UnionRule(InferDependenciesRequest, InferNfpmPackageScriptsDependencies),
+    ]