[bug#44178] Add a Go Module Importer

[Katherine Cox-Buday <cox.katherine.e@gmail.com>]

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From cc92cbcf5ae89891f478f319e955419800bdfcf9 Mon Sep 17 00:00:00 2001
From: Katherine Cox-Buday <cox.katherine.e@gmail.com>
Date: Thu, 22 Oct 2020 19:40:17 -0500
Subject: [PATCH] * guix/import/go.scm: Created Go Importer *
 guix/scripts/import.scm: Created Go Importer Subcommand * guix/import/go.scm
 (importers): Added Go Importer Subcommand

---
 guix/import/go.scm         | 276 +++++++++++++++++++++++++++++++++++++
 guix/scripts/import.scm    |   2 +-
 guix/scripts/import/go.scm | 118 ++++++++++++++++
 3 files changed, 395 insertions(+), 1 deletion(-)
 create mode 100644 guix/import/go.scm
 create mode 100644 guix/scripts/import/go.scm

diff --git a/guix/import/go.scm b/guix/import/go.scm
new file mode 100644
index 0000000000..61009f3565
--- /dev/null
+++ b/guix/import/go.scm
@@ -0,0 +1,276 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2020 Katherine Cox-Buday <cox.katherine.e@gmail.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix import go)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 rdelim)
+  #:use-module (ice-9 receive)
+  #:use-module (ice-9 regex)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (guix json)
+  #:use-module ((guix download) #:prefix download:)
+  #:use-module (guix import utils)
+  #:use-module (guix import json)
+  #:use-module (guix packages)
+  #:use-module (guix upstream)
+  #:use-module (guix utils)
+  #:use-module ((guix licenses) #:prefix license:)
+  #:use-module (guix base16)
+  #:use-module (guix base32)
+  #:use-module (guix build download)
+  #:use-module (web uri)
+
+  #:export (go-module->guix-package
+            go-module-recursive-import
+            infer-module-root))
+
+(define (escape-capital-letters s)
+  "To avoid ambiguity when serving from case-insensitive file systems, the
+$module and $version elements are case-encoded by replacing every uppercase
+letter with an exclamation mark followed by the corresponding lower-case
+letter."
+  (let ((escaped-string (string)))
+    (string-for-each-index
+     (lambda (i)
+       (let ((c (string-ref s i)))
+         (set! escaped-string
+           (string-concatenate
+            (list escaped-string
+                  (if (char-upper-case? c) "!" "")
+                  (string (char-downcase c)))))))
+     s)
+    escaped-string))
+
+(define (fetch-latest-version goproxy-url module-path)
+  "Fetches the version number of the latest version for MODULE-PATH from the
+given GOPROXY-URL server."
+  (assoc-ref
+   (json-fetch (format #f "~a/~a/@latest" goproxy-url
+                       (escape-capital-letters module-path)))
+   "Version"))
+
+(define (fetch-go.mod goproxy-url module-path version file)
+  "Fetches go.mod from the given GOPROXY-URL server for the given MODULE-PATH
+and VERSION."
+  (url-fetch (format #f "~a/~a/@v/~a.mod" goproxy-url
+                     (escape-capital-letters module-path)
+                     (escape-capital-letters version))
+             file
+             #:print-build-trace? #f))
+
+(define (parse-go.mod go.mod-path)
+  "Parses a go.mod file and returns an alist of module path to version."
+  (with-input-from-file go.mod-path
+    (lambda ()
+      (let ((in-require? #f)
+            (requirements (list)))
+        (do ((line (read-line) (read-line)))
+            ((eof-object? line))
+          (set! line (string-trim line))
+          ;; The parser is either entering, within, exiting, or after the
+          ;; require block. The Go toolchain is trustworthy so edge-cases like
+          ;; double-entry, etc. need not complect the parser.
+          (cond
+           ((string=? line "require (")
+            (set! in-require? #t))
+           ((and in-require? (string=? line ")"))
+            (set! in-require? #f))
+           (in-require?
+            (let* ((requirement (string-split line #\space))
+                   ;; Modules should be unquoted
+                   (module-path (string-delete #\" (car requirement)))
+                   (version (list-ref requirement 1)))
+              (set! requirements (acons module-path version requirements))))
+           ((string-prefix? "replace" line)
+            (let* ((requirement (string-split line #\space))
+                   (module-path (list-ref requirement 1))
+                   (new-module-path (list-ref requirement 3))
+                   (version (list-ref requirement 4)))
+              (set! requirements (assoc-remove! requirements module-path))
+              (set! requirements (acons new-module-path version requirements))))))
+        requirements))))
+
+(define (module-path-without-major-version module-path)
+  "Go modules can be appended with a major version indicator,
+e.g. /v3. Sometimes it is desirable to work with the root module path. For
+instance, for a module path github.com/foo/bar/v3 this function returns
+github.com/foo/bar."
+  (let ((m (string-match "(.*)\\/v[0-9]+$" module-path)))
+    (if m
+        (match:substring m 1)
+        module-path)))
+
+(define (infer-module-root module-path)
+  "Go modules can be defined at any level of a repository's tree, but querying
+for the meta tag usually can only be done at the webpage at the root of the
+repository. Therefore, it is sometimes necessary to try and derive a module's
+root path from its path. For a set of well-known forges, the pattern of what
+consists of a module's root page is known before hand."
+  ;; See the following URL for the official Go equivalent:
+  ;; https://github.com/golang/go/blob/846dce9d05f19a1f53465e62a304dea21b99f910/src/cmd/go/internal/vcs/vcs.go#L1026-L1087
+  (define-record-type <scs>
+    (make-scs url-prefix root-regex type)
+    scs?
+    (url-prefix	scs-url-prefix)
+    (root-regex scs-root-regex)
+    (type	scs-type))
+  (let* ((known-scs
+          (list
+           (make-scs
+            "github.com"
+            "^(github\\.com/[A-Za-z0-9_.\\-]+/[A-Za-z0-9_.\\-]+)(/[A-Za-z0-9_.\\-]+)*$"
+            'git)
+           (make-scs
+            "bitbucket.org"
+            "^(bitbucket\\.org/([A-Za-z0-9_.\\-]+/[A-Za-z0-9_.\\-]+))(/[A-Za-z0-9_.\\-]+)*$`"
+            'unknown)
+           (make-scs
+            "hub.jazz.net/git/"
+            "^(hub\\.jazz\\.net/git/[a-z0-9]+/[A-Za-z0-9_.\\-]+)(/[A-Za-z0-9_.\\-]+)*$"
+            'git)
+           (make-scs
+            "git.apache.org"
+            "^(git\\.apache\\.org/[a-z0-9_.\\-]+\\.git)(/[A-Za-z0-9_.\\-]+)*$"
+            'git)
+           (make-scs
+            "git.openstack.org"
+            "^(git\\.openstack\\.org/[A-Za-z0-9_.\\-]+/[A-Za-z0-9_.\\-]+)(\\.git)?(/[A-Za-z0-9_.\\-]+)*$"
+            'git)))
+         (scs (find (lambda (scs) (string-prefix? (scs-url-prefix scs) module-path))
+                    known-scs)))
+    (if scs
+        (match:substring (string-match (scs-root-regex scs) module-path) 1)
+        module-path)))
+
+(define (to-guix-package-name module-path)
+  "Converts a module's path to the canonical Guix format for Go packages."
+  (string-downcase
+   (string-append "go-"
+                  (string-replace-substring
+                   (string-replace-substring
+                    ;; Guix has its own field for version
+                    (module-path-without-major-version module-path)
+                    "." "-")
+                   "/" "-"))))
+
+(define (fetch-module-meta-data module-path)
+  "Fetches module meta-data from a module's landing page. This is necessary
+because goproxy servers don't currently provide all the information needed to
+build a package."
+  (let* ((port (http-fetch (string->uri (format #f "https://~a?go-get=1" module-path))))
+         (module-metadata #f)
+         (meta-tag-prefix "<meta name=\"go-import\" content=\"")
+         (meta-tag-prefix-length (string-length meta-tag-prefix)))
+    (do ((line (read-line port) (read-line port)))
+        ((or (eof-object? line)
+             module-metadata))
+      (let ((meta-tag-index (string-contains line meta-tag-prefix)))
+        (when meta-tag-index
+          (let* ((start (+ meta-tag-index meta-tag-prefix-length))
+                 (end (string-index line #\" start)))
+            (set! module-metadata
+              (string-split (substring/shared line start end) #\space))))))
+    (close-port port)
+    module-metadata))
+
+(define (module-meta-data-scs meta-data)
+  "Return the source control system specified by a module's meta-data."
+  (string->symbol (list-ref meta-data 1)))
+
+(define (module-meta-data-repo-url meta-data goproxy-url)
+  "Return the URL where the fetcher which will be used can download the source
+control."
+  (if (member (module-meta-data-scs meta-data) '(fossil mod))
+      goproxy-url
+      (list-ref meta-data 2)))
+
+(define (source-uri scs-type scs-repo-url file)
+  "Generate the `origin' block of a package depending on what type of source
+control system is being used."
+  (case scs-type
+    ((git)
+     `(origin
+        (method git-fetch)
+        (uri (git-reference
+              (url ,scs-repo-url)
+              (commit (string-append "v" version))))
+        (file-name (git-file-name name version))
+        (sha256
+         (base32
+          ,(guix-hash-url file)))))
+    ((hg)
+     `(origin
+        (method hg-fetch)
+        (uri (hg-reference
+              (url ,scs-repo-url)
+              (changeset ,version)))
+        (file-name (format #f "~a-~a-checkout" name version))))
+    ((svn)
+     `(origin
+        (method svn-fetch)
+        (uri (svn-reference
+              (url ,scs-repo-url)
+              (revision (string->number version))
+              (recursive? #f)))
+        (file-name (format #f "~a-~a-checkout" name version))
+        (sha256
+         (base32
+          ,(guix-hash-url file)))))
+    (else
+     (raise-exception (format #f "unsupported scs type: ~a" scs-type)))))
+
+(define* (go-module->guix-package module-path #:key (goproxy-url "https://proxy.golang.org"))
+  (call-with-temporary-output-file
+   (lambda (temp port)
+     (let* ((latest-version (fetch-latest-version goproxy-url module-path))
+            (go.mod-path (fetch-go.mod goproxy-url module-path latest-version
+                                       temp))
+            (dependencies (map car (parse-go.mod temp)))
+            (guix-name (to-guix-package-name module-path))
+            (root-module-path (infer-module-root module-path))
+            ;; SCS type and URL are not included in goproxy information. For
+            ;; this we need to fetch it from the official module page.
+            (meta-data (fetch-module-meta-data root-module-path))
+            (scs-type (module-meta-data-scs meta-data))
+            (scs-repo-url (module-meta-data-repo-url meta-data goproxy-url)))
+       (values
+        `(package
+           (name ,guix-name)
+           ;; Elide the "v" prefix Go uses
+           (version ,(string-trim latest-version #\v))
+           (source
+            ,(source-uri scs-type scs-repo-url temp))
+           (build-system go-build-system)
+           ,@(maybe-inputs (map to-guix-package-name dependencies))
+           ;; TODO(katco): It would be nice to make an effort to fetch this
+           ;; from known forges, e.g. GitHub
+           (home-page ,(format #f "https://~a" root-module-path))
+           (synopsis "A Go package")
+           (description ,(format #f "~a is a Go package." guix-name))
+           (license #f))
+        dependencies)))))
+
+(define* (go-module-recursive-import package-name
+                                     #:key (goproxy-url "https://proxy.golang.org"))
+  (recursive-import package-name #f
+                    #:repo->guix-package
+                    (lambda (name _)
+                      (go-module->guix-package name
+                                               #:goproxy-url goproxy-url))
+                    #:guix-name to-guix-package-name))
diff --git a/guix/scripts/import.scm b/guix/scripts/import.scm
index 0a3863f965..1d2b45d942 100644
--- a/guix/scripts/import.scm
+++ b/guix/scripts/import.scm
@@ -77,7 +77,7 @@ rather than \\n."
 ;;;
 
 (define importers '("gnu" "nix" "pypi" "cpan" "hackage" "stackage" "elpa" "gem"
-                    "cran" "crate" "texlive" "json" "opam"))
+                    "go" "cran" "crate" "texlive" "json" "opam"))
 
 (define (resolve-importer name)
   (let ((module (resolve-interface
diff --git a/guix/scripts/import/go.scm b/guix/scripts/import/go.scm
new file mode 100644
index 0000000000..000039769c
--- /dev/null
+++ b/guix/scripts/import/go.scm
@@ -0,0 +1,118 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2020 Katherine Cox-Buday <cox.katherine.e@gmail.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix scripts import go)
+  #:use-module (guix ui)
+  #:use-module (guix utils)
+  #:use-module (guix scripts)
+  #:use-module (guix import go)
+  #:use-module (guix scripts import)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
+  #:use-module (srfi srfi-37)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 format)
+  #:export (guix-import-go))
+
+\f
+;;;
+;;; Command-line options.
+;;;
+
+(define %default-options
+  '())
+
+(define (show-help)
+  (display (G_ "Usage: guix import go PACKAGE-PATH
+Import and convert the Go module for PACKAGE-PATH.\n"))
+  (display (G_ "
+  -h, --help             display this help and exit"))
+  (display (G_ "
+  -V, --version          display version information and exit"))
+  (display (G_ "
+  -r, --recursive        generate package expressions for all Go modules\
+ that are not yet in Guix"))
+  (display (G_ "
+  -p, --goproxy=GOPROXY  specify which goproxy server to use"))
+  (newline)
+  (show-bug-report-information))
+
+(define %options
+  ;; Specification of the command-line options.
+  (cons* (option '(#\h "help") #f #f
+                 (lambda args
+                   (show-help)
+                   (exit 0)))
+         (option '(#\V "version") #f #f
+                 (lambda args
+                   (show-version-and-exit "guix import go")))
+         (option '(#\r "recursive") #f #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'recursive #t result)))
+         (option '(#\p "goproxy") #t #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'goproxy
+                               (string->symbol arg)
+                               (alist-delete 'goproxy result))))
+         %standard-import-options))
+
+\f
+;;;
+;;; Entry point.
+;;;
+
+(define (guix-import-go . args)
+  (define (parse-options)
+    ;; Return the alist of option values.
+    (args-fold* args %options
+                (lambda (opt name arg result)
+                  (leave (G_ "~A: unrecognized option~%") name))
+                (lambda (arg result)
+                  (alist-cons 'argument arg result))
+                %default-options))
+
+  (let* ((opts (parse-options))
+         (args (filter-map (match-lambda
+                             (('argument . value)
+                              value)
+                             (_ #f))
+                           (reverse opts))))
+    (match args
+      ((module-name)
+       (if (assoc-ref opts 'recursive)
+           (map (match-lambda
+                  ((and ('package ('name name) . rest) pkg)
+                   `(define-public ,(string->symbol name)
+                      ,pkg))
+                  (_ #f))
+                (go-module-recursive-import module-name
+                                            #:goproxy-url
+                                            (or (assoc-ref opts 'goproxy)
+                                                "https://proxy.golang.org")))
+           (let ((sexp (go-module->guix-package module-name
+                                                #:goproxy-url
+                                                (or (assoc-ref opts 'goproxy)
+                                                    "https://proxy.golang.org"))))
+             (unless sexp
+               (leave (G_ "failed to download meta-data for module '~a'~%")
+                      module-name))
+             sexp)))
+      (()
+       (leave (G_ "too few arguments~%")))
+      ((many ...)
+       (leave (G_ "too many arguments~%"))))))
-- 
2.28.0


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-- 
Katherine