Add scripts to generate ghcup metadata on nightly and release pipelines

1. A python script in .gitlab/rel_eng/mk-ghcup-metadata which generates
   suitable metadata for consumption by GHCUp for the relevant
   pipelines.

  - The script generates the metadata just as the ghcup maintainers
    want, without taking into account platform/library combinations. It
    is updated manually when the mapping changes.

  - The script downloads the bindists which ghcup wants to distribute,
    calculates the hash and generates the yaml in the correct structure.

  - The script is documented in the .gitlab/rel_eng/mk-ghcup-metadata/README.mk file

1a. The script requires us to understand the mapping from platform ->
    job. To choose the preferred bindist for each platform the
    .gitlab/gen_ci.hs script is modified to allow outputting a metadata
    file which answers the question about which job produces the
    bindist which we want to distribute to users for a specific
    platform.

2. Pipelines to run on nightly and release jobs to generate metadata

  - ghcup-metadata-nightly: Generates metadata which points directly to
    artifacts in the nightly job.

  - ghcup-metadata-release: Generates metadata suitable for inclusion
    directly in ghcup by pointing to the downloads folder where the
    bindist will be uploaded to.

2a. Trigger jobs which test the generated metadata in the downstream
    `ghccup-ci` repo. See that repo for documentation about what is
    tested and how but essentially we test in a variety of clean images
    that ghcup can download and install the bindists we say exist in our
    metadata.

6 files changed, 362 insertions, 0 deletions

diff --git a/.gitlab/rel_eng/default.nix b/.gitlab/rel_eng/default.nix
index 42435ba476..4cd6e98499 100644
--- a/.gitlab/rel_eng/default.nix
+++ b/.gitlab/rel_eng/default.nix
@@ -5,6 +5,7 @@ let sources = import ./nix/sources.nix; in
 with nixpkgs;
 let
   fetch-gitlab-artifacts = nixpkgs.callPackage ./fetch-gitlab-artifacts {};
+  mk-ghcup-metadata = nixpkgs.callPackage ./mk-ghcup-metadata { fetch-gitlab=fetch-gitlab-artifacts;};
 
 
   bindistPrepEnv = pkgs.buildFHSUserEnv {
@@ -50,5 +51,6 @@ in
     paths = [
       scripts
       fetch-gitlab-artifacts
+      mk-ghcup-metadata
     ];
   }
diff --git a/.gitlab/rel_eng/mk-ghcup-metadata/.gitignore b/.gitlab/rel_eng/mk-ghcup-metadata/.gitignore
new file mode 100644
index 0000000000..1b01e3c7e9
--- /dev/null
+++ b/.gitlab/rel_eng/mk-ghcup-metadata/.gitignore
@@ -0,0 +1,3 @@
+result
+fetch-gitlab
+out
diff --git a/.gitlab/rel_eng/mk-ghcup-metadata/README.mkd b/.gitlab/rel_eng/mk-ghcup-metadata/README.mkd
new file mode 100644
index 0000000000..fe16439b61
--- /dev/null
+++ b/.gitlab/rel_eng/mk-ghcup-metadata/README.mkd
@@ -0,0 +1,56 @@
+# mk-ghcup-metadata
+
+This script is used to automatically generate metadata suitable for consumption by
+GHCUp.
+
+# Usage
+
+```
+nix run -f .gitlab/rel_eng/ -c ghcup-metadata
+```
+
+```
+options:
+  -h, --help            show this help message and exit
+  --metadata METADATA   Path to GHCUp metadata
+  --pipeline-id PIPELINE_ID
+                        Which pipeline to generate metadata for
+  --release-mode        Generate metadata which points to downloads folder
+  --fragment            Output the generated fragment rather than whole modified file
+  --version VERSION     Version of the GHC compiler
+```
+
+The script also requires the `.gitlab/jobs-metadata.yaml` file which can be generated
+by running `.gitlab/generate_jobs_metadata` script if you want to run it locally.
+
+
+## CI Pipelines
+
+The metadata is generated by the nightly and release pipelines.
+
+* Nightly pipelines generate metadata where the bindist URLs point immediatley to
+  nightly artifacts.
+* Release jobs can pass the `--release-mode` flag which downloads the artifacts from
+  the pipeline but the final download URLs for users point into the downloads folder.
+
+The mapping from platform to bindist is not clever, it is just what the GHCUp developers
+tell us to use.
+
+## Testing Pipelines
+
+The metadata is tested by the `ghcup-ci` repo which is triggered by the
+`ghcup-metadata-testing-nightly` job.
+
+This job sets the following variables which are then used by the downstream job
+to collect the metadata from the correct place:
+
+* `UPSTREAM_PIPELINE_ID`  - The pipeline ID which the generated metadata lives in
+* `UPSTREAM_PROJECT_ID`   - The project ID for the upstream project (almost always `1` (for ghc/ghc))
+* `UPSTREAM_JOB_NAME`     - The job which the metadata belongs to (ie `ghcup-metadata-nightly`)
+* `UPSTREAM_PROJECT_PATH` - The path of the upstream project (almost always ghc/ghc)
+
+Nightly pipelines are tested automaticaly but release pipelines are manually triggered
+as the testing requires the bindists to be uploaded into the final release folder.
+
+
+
diff --git a/.gitlab/rel_eng/mk-ghcup-metadata/default.nix b/.gitlab/rel_eng/mk-ghcup-metadata/default.nix
new file mode 100644
index 0000000000..61498503a4
--- /dev/null
+++ b/.gitlab/rel_eng/mk-ghcup-metadata/default.nix
@@ -0,0 +1,13 @@
+{ nix-gitignore, python3Packages, fetch-gitlab }:
+
+let
+  ghcup-metadata = { buildPythonPackage, python-gitlab, pyyaml }:
+    buildPythonPackage {
+      pname = "ghcup-metadata";
+      version = "0.0.1";
+      src = nix-gitignore.gitignoreSource [] ./.;
+      propagatedBuildInputs = [fetch-gitlab python-gitlab pyyaml ];
+      preferLocalBuild = true;
+    };
+in
+python3Packages.callPackage ghcup-metadata { }
diff --git a/.gitlab/rel_eng/mk-ghcup-metadata/mk_ghcup_metadata.py b/.gitlab/rel_eng/mk-ghcup-metadata/mk_ghcup_metadata.py
new file mode 100755
index 0000000000..394fb4e298
--- /dev/null
+++ b/.gitlab/rel_eng/mk-ghcup-metadata/mk_ghcup_metadata.py
@@ -0,0 +1,274 @@
+#! /usr/bin/env nix-shell
+#! nix-shell -i python3 -p curl  "python3.withPackages (ps:[ps.pyyaml ps.python-gitlab ])"
+
+"""
+A tool for generating metadata suitable for GHCUp
+
+There are two ways to prepare metadata:
+
+* From a nightly pipeline.
+* From a release pipeline.
+
+In any case the script takes the same arguments:
+
+
+* --metadata: The path to existing GHCup metadata to which we want to add the new entry.
+* --version: GHC version of the pipeline
+* --pipeline-id: The pipeline to generate metadata for
+* --release-mode: Download from a release pipeline but generate URLs to point to downloads folder.
+* --fragment: Only print out the updated fragment rather than the modified file
+
+The script will then download the relevant bindists to compute the hashes. The
+generated metadata is printed to stdout.
+
+The metadata can then be used by passing the `--url-source` flag to ghcup.
+"""
+
+from subprocess import run, check_call
+from getpass import getpass
+import shutil
+from pathlib import Path
+from typing import NamedTuple, Callable, List, Dict, Optional
+import tempfile
+import re
+import pickle
+import os
+import yaml
+import gitlab
+from urllib.request import urlopen
+import hashlib
+import sys
+import json
+import urllib.parse
+import fetch_gitlab
+
+def eprint(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+
+gl = gitlab.Gitlab('https://gitlab.haskell.org', per_page=100)
+
+# TODO: Take this file as an argument
+metadata_file = ".gitlab/jobs-metadata.json"
+
+release_base = "https://downloads.haskell.org/~ghc/{version}/ghc-{version}-{bindistName}"
+
+eprint(f"Reading job metadata from {metadata_file}.")
+with open(metadata_file, 'r') as f:
+  job_mapping = json.load(f)
+
+eprint(f"Supported platforms: {job_mapping.keys()}")
+
+
+# Artifact precisely specifies a job what the bindist to download is called.
+class Artifact(NamedTuple):
+    job_name: str
+    name: str
+    subdir: str
+
+# Platform spec provides a specification which is agnostic to Job
+# PlatformSpecs are converted into Artifacts by looking in the jobs-metadata.json file.
+class PlatformSpec(NamedTuple):
+    name: str
+    subdir: str
+
+source_artifact = Artifact('source-tarball', 'ghc-{version}-src.tar.xz', 'ghc-{version}' )
+
+def debian(arch, n):
+    return linux_platform(arch, "{arch}-linux-deb{n}".format(arch=arch, n=n))
+
+def darwin(arch):
+    return PlatformSpec ( '{arch}-darwin'.format(arch=arch)
+                        , 'ghc-{version}-{arch}-apple-darwin'.format(arch=arch, version="{version}") )
+
+windowsArtifact = PlatformSpec ( 'x86_64-windows'
+                               , 'ghc-{version}-x86_64-unknown-mingw' )
+
+def centos(n):
+    return linux_platform("x86_64", "x86_64-linux-centos{n}".format(n=n))
+
+def fedora(n):
+    return linux_platform("x86_64", "x86_64-linux-fedora{n}".format(n=n))
+
+def alpine(n):
+    return linux_platform("x86_64", "x86_64-linux-alpine{n}".format(n=n))
+
+def linux_platform(arch, opsys):
+    return PlatformSpec( opsys, 'ghc-{version}-{arch}-unknown-linux'.format(version="{version}", arch=arch) )
+
+
+base_url = 'https://gitlab.haskell.org/ghc/ghc/-/jobs/{job_id}/artifacts/raw/{artifact_name}'
+
+
+hash_cache = {}
+
+# Download a URL and return its hash
+def download_and_hash(url):
+    if url in hash_cache: return hash_cache[url]
+    eprint ("Opening {}".format(url))
+    response = urlopen(url)
+    sz = response.headers['content-length']
+    hasher = hashlib.sha256()
+    CHUNK = 2**22
+    for n,text in enumerate(iter(lambda: response.read(CHUNK), '')):
+        if not text: break
+        eprint("{:.2f}% {} / {} of {}".format (((n + 1) * CHUNK) / int(sz) * 100, (n + 1) * CHUNK, sz, url))
+        hasher.update(text)
+    digest = hasher.hexdigest()
+    hash_cache[url] = digest
+    return digest
+
+# Make the metadata for one platform.
+def mk_one_metadata(release_mode, version, job_map, artifact):
+    job_id = job_map[artifact.job_name].id
+
+    url = base_url.format(job_id=job_id, artifact_name=urllib.parse.quote_plus(artifact.name.format(version=version)))
+
+    # In --release-mode, the URL in the metadata needs to point into the downloads folder
+    # rather then the pipeline.
+    if release_mode:
+        final_url = release_base.format( version=version
+                                       , bindistName=urllib.parse.quote_plus(f"{fetch_gitlab.job_triple(artifact.job_name)}.tar.xz"))
+    else:
+        final_url = url
+
+    eprint(f"Making metadata for: {artifact}")
+    eprint(f"Bindist URL: {url}")
+    eprint(f"Download URL: {final_url}")
+
+    # Download and hash from the release pipeline, this must not change anyway during upload.
+    h = download_and_hash(url)
+
+    res = { "dlUri": final_url, "dlSubdir": artifact.subdir.format(version=version), "dlHash" : h }
+    eprint(res)
+    return res
+
+# Turns a platform into an Artifact respecting pipeline_type
+# Looks up the right job to use from the .gitlab/jobs-metadata.json file
+def mk_from_platform(pipeline_type, platform):
+    info = job_mapping[platform.name][pipeline_type]
+    eprint(f"From {platform.name} / {pipeline_type} selecting {info['name']}")
+    return Artifact(info['name'] , f"{info['jobInfo']['bindistName']}.tar.xz", platform.subdir)
+
+# Generate the new metadata for a specific GHC mode etc
+def mk_new_yaml(release_mode, version, pipeline_type, job_map):
+    def mk(platform):
+        eprint("\n=== " + platform.name + " " + ('=' * (75 - len(platform.name))))
+        return mk_one_metadata(release_mode, version, job_map, mk_from_platform(pipeline_type, platform))
+
+    # Here are all the bindists we can distribute
+    centos7 = mk(centos(7))
+    fedora33 = mk(fedora(33))
+    darwin_x86 = mk(darwin("x86_64"))
+    darwin_arm64 = mk(darwin("aarch64"))
+    windows = mk(windowsArtifact)
+    alpine3_12 = mk(alpine("3_12"))
+    deb9 = mk(debian("x86_64", 9))
+    deb10 = mk(debian("x86_64", 10))
+    deb11 = mk(debian("x86_64", 11))
+    deb10_arm64 = mk(debian("aarch64", 10))
+    deb9_i386 = mk(debian("i386", 9))
+
+    source = mk_one_metadata(release_mode, version, job_map, source_artifact)
+
+    # The actual metadata, this is not a precise science, but just what the ghcup
+    # developers want.
+
+    a64 = { "Linux_Debian": { "< 10": deb9
+                           , "(>= 10 && < 11)": deb10
+                           , ">= 11": deb11
+                           , "unknown_versioning": deb11 }
+          , "Linux_Ubuntu" : { "unknown_versioning": deb10
+                             , "( >= 16 && < 19 )": deb9
+                             }
+          , "Linux_Mint"   : { "< 20": deb9
+                             , ">= 20": deb10 }
+          , "Linux_CentOS"  : { "( >= 7 && < 8 )" : centos7
+                              , "unknown_versioning" : centos7  }
+          , "Linux_Fedora"  : { ">= 33": fedora33
+                              , "unknown_versioning": centos7 }
+          , "Linux_RedHat"  : { "unknown_versioning": centos7 }
+          #MP: Replace here with Rocky8 when that job is in the pipeline
+          , "Linux_UnknownLinux" : { "unknown_versioning": fedora33 }
+          , "Darwin" : { "unknown_versioning" : darwin_x86 }
+          , "Windows" : { "unknown_versioning" :  windows }
+          , "Linux_Alpine" : { "unknown_versioning": alpine3_12 }
+
+          }
+
+    a32 = { "Linux_Debian": { "<10": deb9_i386, "unknown_versioning": deb9_i386 }
+          , "Linux_Ubuntu": { "unknown_versioning": deb9_i386 }
+          , "Linux_Mint" : { "unknown_versioning": deb9_i386 }
+          , "Linux_UnknownLinux" : { "unknown_versioning": deb9_i386 }
+          }
+
+    arm64 = { "Linux_UnknownLinux": { "unknown_versioning": deb10_arm64 }
+            , "Darwin": { "unknown_versioning": darwin_arm64 }
+            }
+
+    if release_mode:
+        version_parts = version.split('.')
+        if len(version_parts) == 3:
+            final_version = version
+        elif len(version_parts) == 4:
+            final_version = '.'.join(version_parts[:2] + [str(int(version_parts[2]) + 1)])
+        change_log = f"https://downloads.haskell.org/~ghc/{version}/docs/users_guide/{final_version}-notes.html"
+    else:
+        change_log =  "https://gitlab.haskell.org"
+
+    return { "viTags": ["Latest", "TODO_base_version"]
+        # Check that this link exists
+        , "viChangeLog": change_log
+        , "viSourceDL": source
+        , "viPostRemove": "*ghc-post-remove"
+        , "viArch": { "A_64": a64
+                    , "A_32": a32
+                    , "A_ARM64": arm64
+                    }
+        }
+
+
+def main() -> None:
+    import argparse
+
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('--metadata', required=True, type=Path, help='Path to GHCUp metadata')
+    parser.add_argument('--pipeline-id', required=True, type=int, help='Which pipeline to generate metadata for')
+    parser.add_argument('--release-mode', action='store_true', help='Generate metadata which points to downloads folder')
+    parser.add_argument('--fragment', action='store_true', help='Output the generated fragment rather than whole modified file')
+    # TODO: We could work out the --version from the project-version CI job.
+    parser.add_argument('--version', required=True, type=str, help='Version of the GHC compiler')
+    args = parser.parse_args()
+
+    project = gl.projects.get(1, lazy=True)
+    pipeline = project.pipelines.get(args.pipeline_id)
+    jobs = pipeline.jobs.list()
+    job_map = { job.name: job for job in jobs }
+    # Bit of a hacky way to determine what pipeline we are dealing with but
+    # the aarch64-darwin job should stay stable for a long time.
+    if 'nightly-aarch64-darwin-validate' in job_map:
+        pipeline_type = 'n'
+        if args.release_mode:
+            raise Exception("Incompatible arguments: nightly pipeline but using --release-mode")
+
+    elif 'release-aarch64-darwin-release' in job_map:
+        pipeline_type = 'r'
+    else:
+        raise Exception("Not a nightly nor release pipeline")
+    eprint(f"Pipeline Type: {pipeline_type}")
+
+
+    new_yaml = mk_new_yaml(args.release_mode, args.version, pipeline_type, job_map)
+    if args.fragment:
+        print(yaml.dump({ args.version : new_yaml }))
+
+    else:
+        with open(args.metadata, 'r') as file:
+            ghcup_metadata = yaml.safe_load(file)
+            ghcup_metadata['ghcupDownloads']['GHC'][args.version] = new_yaml
+            print(yaml.dump(ghcup_metadata))
+
+
+if __name__ == '__main__':
+    main()
+
diff --git a/.gitlab/rel_eng/mk-ghcup-metadata/setup.py b/.gitlab/rel_eng/mk-ghcup-metadata/setup.py
new file mode 100644
index 0000000000..d4f4efe5e4
--- /dev/null
+++ b/.gitlab/rel_eng/mk-ghcup-metadata/setup.py
@@ -0,0 +1,14 @@
+#!/usr/bin/env python
+
+from distutils.core import setup
+
+setup(name='ghcup-metadata',
+      author='Matthew Pickering',
+      author_email='matthew@well-typed.com',
+      py_modules=['mk_ghcup_metadata'],
+      entry_points={
+          'console_scripts': [
+              'ghcup-metadata=mk_ghcup_metadata:main',
+          ]
+      }
+     )