;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2021-2023 Ludovic Courtès <ludo@gnu.org>
;;;
;;; 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 read-print)
#:use-module (ice-9 control)
#:use-module (ice-9 match)
#:use-module (ice-9 rdelim)
#:use-module (ice-9 vlist)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-26)
#:use-module (srfi srfi-34)
#:use-module (srfi srfi-35)
#:use-module (guix i18n)
#:use-module ((guix diagnostics)
#:select (formatted-message
&fix-hint &error-location
location))
#:export (pretty-print-with-comments
pretty-print-with-comments/splice
read-with-comments
read-with-comments/sequence
object->string*
blank?
vertical-space
vertical-space?
vertical-space-height
canonicalize-vertical-space
page-break
page-break?
<comment>
comment
comment?
comment->string
comment-margin?
canonicalize-comment))
;;; Commentary:
;;;
;;; This module provides a comment-preserving reader and a comment-preserving
;;; pretty-printer smarter than (ice-9 pretty-print).
;;;
;;; Code:
;;;
;;; Comment-preserving reader.
;;;
(define <blank>
;; The parent class for "blanks".
(make-record-type '<blank> '()
(lambda (obj port)
(format port "#<blank ~a>"
(number->string (object-address obj) 16)))
#:extensible? #t))
(define blank? (record-predicate <blank>))
(define <vertical-space>
(make-record-type '<vertical-space> '(height)
#:parent <blank>
#:extensible? #f))
(define vertical-space? (record-predicate <vertical-space>))
(define vertical-space (record-type-constructor <vertical-space>))
(define vertical-space-height (record-accessor <vertical-space> 'height))
(define canonicalize-vertical-space
(let ((unit (vertical-space 1)))
(lambda (space)
"Return a vertical space corresponding to a single blank line."
unit)))
(define <page-break>
(make-record-type '<page-break> '()
#:parent <blank>
#:extensible? #f))
(define page-break? (record-predicate <page-break>))
(define page-break
(let ((break ((record-type-constructor <page-break>))))
(lambda ()
break)))
(define <comment>
;; Comments.
(make-record-type '<comment> '(str margin?)
#:parent <blank>
#:extensible? #f))
(define comment? (record-predicate <comment>))
(define string->comment (record-type-constructor <comment>))
(define comment->string (record-accessor <comment> 'str))
(define comment-margin? (record-accessor <comment> 'margin?))
(define* (comment str #:optional margin?)
"Return a new comment made from STR. When MARGIN? is true, return a margin
comment; otherwise return a line comment. STR must start with a semicolon and
end with newline, otherwise an error is raised."
(when (or (string-null? str)
(not (eqv? #\; (string-ref str 0)))
(not (string-suffix? "\n" str)))
(raise (condition
(&message (message "invalid comment string")))))
(string->comment str margin?))
(define char-set:whitespace-sans-page-break
;; White space, excluding #\page.
(char-set-difference char-set:whitespace (char-set #\page)))
(define (space? chr)
"Return true if CHR is white space, except for page breaks."
(char-set-contains? char-set:whitespace-sans-page-break chr))
(define (read-vertical-space port)
"Read from PORT until a non-vertical-space character is met, and return a
single <vertical-space> record."
(let loop ((height 1))
(match (read-char port)
(#\newline (loop (+ 1 height)))
((? eof-object?) (vertical-space height))
((? space?) (loop height))
(chr (unread-char chr port) (vertical-space height)))))
(define (read-until-end-of-line port)
"Read white space from PORT until the end of line, included."
(let loop ()
(match (read-char port)
(#\newline #t)
((? eof-object?) #t)
((? space?) (loop))
(chr (unread-char chr port)))))
(define* (read-with-comments port #:key (blank-line? #t))
"Like 'read', but include <blank> objects when they're encountered. When
BLANK-LINE? is true, assume PORT is at the beginning of a new line."
;; Note: Instead of implementing this functionality in 'read' proper, which
;; is the best approach long-term, this code is a layer on top of 'read',
;; such that we don't have to rely on a specific Guile version.
(define dot (list 'dot))
(define (dot? x) (eq? x dot))
(define (missing-closing-paren-error)
(raise (make-compound-condition
(formatted-message (G_ "unexpected end of file"))
(condition
(&error-location
(location (match (port-filename port)
(#f #f)
(file (location file
(port-line port)
(port-column port))))))
(&fix-hint
(hint (G_ "Did you forget a closing parenthesis?")))))))
(define (reverse/dot lst)
;; Reverse LST and make it an improper list if it contains DOT.
(let loop ((result '())
(lst lst))
(match lst
(() result)
(((? dot?) . rest)
(if (pair? rest)
(let ((dotted (reverse rest)))
(set-cdr! (last-pair dotted) (car result))
dotted)
(car result)))
((x . rest) (loop (cons x result) rest)))))
(let loop ((blank-line? blank-line?)
(return (const 'unbalanced)))
(match (read-char port)
((? eof-object? eof)
eof) ;oops!
(chr
(cond ((eqv? chr #\newline)
(if blank-line?
(read-vertical-space port)
(loop #t return)))
((eqv? chr #\page)
;; Assume that a page break is on a line of its own and read
;; subsequent white space and newline.
(read-until-end-of-line port)
(page-break))
((char-set-contains? char-set:whitespace chr)
(loop blank-line? return))
((memv chr '(#\( #\[))
(let/ec return
(let liip ((lst '()))
(define item
(loop (match lst
(((? blank?) . _) #t)
(_ #f))
(lambda ()
(return (reverse/dot lst)))))
(if (eof-object? item)
(missing-closing-paren-error)
(liip (cons item lst))))))
((memv chr '(#\) #\]))
(return))
((eq? chr #\')
(list 'quote (loop #f return)))
((eq? chr #\`)
(list 'quasiquote (loop #f return)))
((eq? chr #\#)
(match (read-char port)
(#\~ (list 'gexp (loop #f return)))
(#\$ (list (match (peek-char port)
(#\@
(read-char port) ;consume
'ungexp-splicing)
(_
'ungexp))
(loop #f return)))
(#\+ (list (match (peek-char port)
(#\@
(read-char port) ;consume
'ungexp-native-splicing)
(_
'ungexp-native))
(loop #f return)))
(chr
(unread-char chr port)
(unread-char #\# port)
(read port))))
((eq? chr #\,)
(list (match (peek-char port)
(#\@
(read-char port)
'unquote-splicing)
(_
'unquote))
(loop #f return)))
((eqv? chr #\;)
(unread-char chr port)
(string->comment (read-line port 'concat)
(not blank-line?)))
(else
(unread-char chr port)
(match (read port)
((and token '#{.}#)
(if (eq? chr #\.) dot token))
(token token))))))))
(define (read-with-comments/sequence port)
"Read from PORT until the end-of-file is reached and return the list of
expressions and blanks that were read."
(let loop ((lst '())
(blank-line? #t))
(match (read-with-comments port #:blank-line? blank-line?)
((? eof-object?)
(reverse! lst))
((? blank? blank)
(loop (cons blank lst) #t))
(exp
(loop (cons exp lst) #f)))))
;;;
;;; Comment-preserving pretty-printer.
;;;
(define-syntax vhashq
(syntax-rules (quote)
((_) vlist-null)
((_ (key (quote (lst ...))) rest ...)
(vhash-consq key '(lst ...) (vhashq rest ...)))
((_ (key value) rest ...)
(vhash-consq key '((() . value)) (vhashq rest ...)))))
(define %special-forms
;; Forms that are indented specially. The number is meant to be understood
;; like Emacs' 'scheme-indent-function' symbol property. When given an
;; alist instead of a number, the alist gives "context" in which the symbol
;; is a special form; for instance, context (modify-phases) means that the
;; symbol must appear within a (modify-phases ...) expression.
(vhashq
('begin 1)
('case 2)
('cond 1)
('lambda 2)
('lambda* 2)
('match-lambda 1)
('match-lambda* 1)
('define 2)
('define* 2)
('define-public 2)
('define*-public 2)
('define-syntax 2)
('define-syntax-rule 2)
('define-module 2)
('define-gexp-compiler 2)
('define-record-type 2)
('define-record-type* 4)
('define-configuration 2)
('package/inherit 2)
('let 2)
('let* 2)
('letrec 2)
('letrec* 2)
('match 2)
('match-record 3)
('match-record-lambda 2)
('when 2)
('unless 2)
('package 1)
('origin 1)
('channel 1)
('modify-inputs 2)
('modify-phases 2)
('add-after '(((modify-phases) . 3)))
('add-before '(((modify-phases) . 3)))
('replace '(((modify-phases) . 2))) ;different from 'modify-inputs'
('parameterize 2)
('substitute* 2)
('substitute-keyword-arguments 2)
('call-with-input-file 2)
('call-with-output-file 2)
('with-output-to-file 2)
('with-input-from-file 2)
('with-directory-excursion 2)
('wrap-program 2)
('wrap-script 2)
;; (gnu system) and (gnu services).
('operating-system 1)
('bootloader-configuration 1)
('mapped-device 1)
('file-system 1)
('swap-space 1)
('user-account 1)
('user-group 1)
('setuid-program 1)
('modify-services 2)
;; (gnu home).
('home-environment 1)))
(define %newline-forms
;; List heads that must be followed by a newline. The second argument is
;; the context in which they must appear. This is similar to a special form
;; of 1, except that indent is 1 instead of 2 columns.
(vhashq
('source '(package))
('git-reference '(uri origin source))
('sha256 '(origin source package))
('arguments '(package))
('list '(arguments package))
('search-paths '(package))
('native-search-paths '(package))
('search-path-specification '())
('services '(operating-system))
('set-xorg-configuration '())
('services '(home-environment))
('home-bash-configuration '(service))
('introduction '(channel))))
(define (prefix? candidate lst)
"Return true if CANDIDATE is a prefix of LST."
(let loop ((candidate candidate)
(lst lst))
(match candidate
(() #t)
((head1 . rest1)
(match lst
(() #f)
((head2 . rest2)
(and (equal? head1 head2)
(loop rest1 rest2))))))))
(define (special-form-lead symbol context)
"If SYMBOL is a special form in the given CONTEXT, return its number of
arguments; otherwise return #f. CONTEXT is a stack of symbols lexically
surrounding SYMBOL."
(match (vhash-assq symbol %special-forms)
(#f #f)
((_ . alist)
(any (match-lambda
((prefix . level)
(and (prefix? prefix context) (- level 1))))
alist))))
(define (newline-form? symbol context)
"Return true if parenthesized expressions starting with SYMBOL must be
followed by a newline."
(let ((matches (vhash-foldq* cons '() symbol %newline-forms)))
(find (cut prefix? <> context)
matches)))
(define (escaped-string str)
"Return STR with backslashes and double quotes escaped. Everything else, in
particular newlines, is left as is."
(list->string
`(#\"
,@(string-fold-right (lambda (chr lst)
(match chr
(#\" (cons* #\\ #\" lst))
(#\\ (cons* #\\ #\\ lst))
(_ (cons chr lst))))
'()
str)
#\")))
(define %natural-whitespace-string-forms
;; When a string has one of these forms as its parent, only double quotes
;; and backslashes are escaped; newlines, tabs, etc. are left as-is.
'(synopsis description G_ N_))
(define (printed-string str context)
"Return the read syntax for STR depending on CONTEXT."
(define (preserve-newlines? str)
(and (> (string-length str) 40)
(string-index str #\newline)))
(match context
(()
(if (preserve-newlines? str)
(escaped-string str)
(object->string str)))
((head . _)
(if (or (memq head %natural-whitespace-string-forms)
(preserve-newlines? str))
(escaped-string str)
(object->string str)))))
(define (string-width str)
"Return the \"width\" of STR--i.e., the width of the longest line of STR."
(apply max (map string-length (string-split str #\newline))))
(define (canonicalize-comment comment indent)
"Canonicalize COMMENT, which is to be printed at INDENT, ensuring it has the
\"right\" number of leading semicolons."
(if (zero? indent)
comment ;leave top-level comments unchanged
(let ((line (string-trim-both
(string-trim (comment->string comment) (char-set #\;)))))
(string->comment (string-append
(if (comment-margin? comment)
";"
(if (string-null? line)
";;" ;no trailing space
";; "))
line "\n")
(comment-margin? comment)))))
(define %not-newline
(char-set-complement (char-set #\newline)))
(define (print-multi-line-comment str indent port)
"Print to PORT STR as a multi-line comment, with INDENT spaces preceding
each line except the first one (they're assumed to be already there)."
;; While 'read-with-comments' only returns one-line comments, user-provided
;; comments might span multiple lines, which is why this is necessary.
(let loop ((lst (string-tokenize str %not-newline)))
(match lst
(() #t)
((last)
(display last port)
(newline port))
((head tail ...)
(display head port)
(newline port)
(display (make-string indent #\space) port)
(loop tail)))))
(define %integer-forms
;; Forms that take an integer as their argument, where said integer should
;; be printed in base other than decimal base.
(letrec-syntax ((vhashq (syntax-rules ()
((_) vlist-null)
((_ (key value) rest ...)
(vhash-consq key value (vhashq rest ...))))))
(vhashq
('chmod 8)
('umask 8)
('mkdir 8)
('mkstemp 8)
('logand 16)
('logior 16)
('logxor 16)
('lognot 16))))
(define (integer->string integer context)
"Render INTEGER as a string using a base suitable based on CONTEXT."
(define (form-base form)
(match (vhash-assq form %integer-forms)
(#f 10)
((_ . base) base)))
(define (octal? form)
(= 8 (form-base form)))
(define base
(match context
((head . tail)
(match (form-base head)
(8 8)
(16 (if (any octal? tail) 8 16))
(10 10)))
(_ 10)))
(string-append (match base
(10 "")
(16 "#x")
(8 "#o"))
(number->string integer base)))
(define %special-non-extended-symbols
;; Special symbols that can be written without the #{...}# notation for
;; extended symbols: 1+, 1-, 123/, etc.
(make-regexp "^[0-9]+[[:graph:]]+$" regexp/icase))
(define (symbol->display-string symbol context)
"Return the most appropriate representation of SYMBOL, resorting to extended
symbol notation only when strictly necessary."
(let ((str (symbol->string symbol)))
(if (regexp-exec %special-non-extended-symbols str)
str ;no need for the #{...}# notation
(object->string symbol))))
(define* (pretty-print-with-comments port obj
#:key
(format-comment
(lambda (comment indent) comment))
(format-vertical-space identity)
(indent 0)
(max-width 78)
(long-list 5))
"Pretty-print OBJ to PORT, attempting to at most MAX-WIDTH character columns
and assuming the current column is INDENT. Comments present in OBJ are
included in the output.
Lists longer than LONG-LIST are written as one element per line. Comments are
passed through FORMAT-COMMENT before being emitted; a useful value for
FORMAT-COMMENT is 'canonicalize-comment'. Vertical space is passed through
FORMAT-VERTICAL-SPACE; a useful value of 'canonicalize-vertical-space'."
(define (list-of-lists? head tail)
;; Return true if HEAD and TAIL denote a list of lists--e.g., a list of
;; 'let' bindings.
(match head
((thing _ ...) ;proper list
(and (not (memq thing
'(quote quasiquote unquote unquote-splicing)))
(pair? tail)))
(_ #f)))
(define (starts-with-line-comment? lst)
;; Return true if LST starts with a line comment.
(match lst
((x . _) (and (comment? x) (not (comment-margin? x))))
(_ #f)))
(let loop ((indent indent)
(column indent)
(delimited? #t) ;true if comes after a delimiter
(context '()) ;list of "parent" symbols
(obj obj))
(define (print-sequence context indent column lst delimited?)
(define long?
(> (length lst) long-list))
(let print ((lst lst)
(first? #t)
(delimited? delimited?)
(column column))
(match lst
(()
column)
((item . tail)
(define newline?
;; Insert a newline if ITEM is itself a list, or if TAIL is long,
;; but only if ITEM is not the first item. Also insert a newline
;; before a keyword.
(and (or (pair? item) long?
(and (keyword? item)
(not (eq? item #:allow-other-keys))))
(not first?) (not delimited?)
(not (blank? item))))
(when newline?
(newline port)
(display (make-string indent #\space) port))
(let ((column (if newline? indent column)))
(print tail
(keyword? item) ;keep #:key value next to one another
(blank? item)
(loop indent column
(or newline? delimited?)
context
item)))))))
(define (sequence-would-protrude? indent lst)
;; Return true if elements of LST written at INDENT would protrude
;; beyond MAX-WIDTH. This is implemented as a cheap test with false
;; negatives to avoid actually rendering all of LST.
(find (match-lambda
((? string? str)
(>= (+ (string-width str) 2 indent) max-width))
((? symbol? symbol)
(>= (+ (string-width (symbol->display-string symbol context))
indent)
max-width))
((? boolean?)
(>= (+ 2 indent) max-width))
(()
(>= (+ 2 indent) max-width))
(_ ;don't know
#f))
lst))
(define (special-form? head)
(special-form-lead head context))
(match obj
((? comment? comment)
(if (comment-margin? comment)
(begin
(display " " port)
(display (comment->string (format-comment comment indent))
port))
(begin
;; When already at the beginning of a line, for example because
;; COMMENT follows a margin comment, no need to emit a newline.
(unless (= column indent)
(newline port)
(display (make-string indent #\space) port))
(print-multi-line-comment (comment->string
(format-comment comment indent))
indent port)))
(display (make-string indent #\space) port)
indent)
((? vertical-space? space)
(unless delimited? (newline port))
(let loop ((i (vertical-space-height (format-vertical-space space))))
(unless (zero? i)
(newline port)
(loop (- i 1))))
(display (make-string indent #\space) port)
indent)
((? page-break?)
(unless delimited? (newline port))
(display #\page port)
(newline port)
(display (make-string indent #\space) port)
indent)
(('quote lst)
(unless delimited? (display " " port))
(display "'" port)
(loop indent (+ column (if delimited? 1 2)) #t context lst))
(('quasiquote lst)
(unless delimited? (display " " port))
(display "`" port)
(loop indent (+ column (if delimited? 1 2)) #t context lst))
(('unquote lst)
(unless delimited? (display " " port))
(display "," port)
(loop indent (+ column (if delimited? 1 2)) #t context lst))
(('unquote-splicing lst)
(unless delimited? (display " " port))
(display ",@" port)
(loop indent (+ column (if delimited? 2 3)) #t context lst))
(('gexp lst)
(unless delimited? (display " " port))
(display "#~" port)
(loop indent (+ column (if delimited? 2 3)) #t context lst))
(('ungexp obj)
(unless delimited? (display " " port))
(display "#$" port)
(loop indent (+ column (if delimited? 2 3)) #t context obj))
(('ungexp-native obj)
(unless delimited? (display " " port))
(display "#+" port)
(loop indent (+ column (if delimited? 2 3)) #t context obj))
(('ungexp-splicing lst)
(unless delimited? (display " " port))
(display "#$@" port)
(loop indent (+ column (if delimited? 3 4)) #t context lst))
(('ungexp-native-splicing lst)
(unless delimited? (display " " port))
(display "#+@" port)
(loop indent (+ column (if delimited? 3 4)) #t context lst))
(((? special-form? head) arguments ...)
;; Special-case 'let', 'lambda', 'modify-inputs', etc. so the second
;; and following arguments are less indented.
(let* ((lead (special-form-lead head context))
(context (cons head context))
(head (symbol->display-string head (cdr context)))
(total (length arguments)))
(unless delimited? (display " " port))
(display "(" port)
(display head port)
(unless (zero? lead)
(display " " port))
;; Print the first LEAD arguments.
(let* ((indent (+ column 2
(if delimited? 0 1)))
(column (+ column 1
(if (zero? lead) 0 1)
(if delimited? 0 1)
(string-length head)))
(initial-indent column))
(define new-column
(let inner ((n lead)
(arguments (take arguments (min lead total)))
(column column))
(if (zero? n)
(begin
(newline port)
(display (make-string indent #\space) port)
indent)
(match arguments
(() column)
((head . tail)
(inner (- n 1) tail
(loop initial-indent column
(= n lead)
context
head)))))))
;; Print the remaining arguments.
(let ((column (print-sequence
context indent new-column
(drop arguments (min lead total))
#t)))
(display ")" port)
(+ column 1)))))
((head tail ...)
(let* ((overflow? (>= column max-width))
(column (if overflow?
(+ indent 1)
(+ column (if delimited? 1 2))))
(newline? (or (newline-form? head context)
(list-of-lists? head tail) ;'let' bindings
(starts-with-line-comment? tail)))
(context (cons head context)))
(if overflow?
(begin
(newline port)
(display (make-string indent #\space) port))
(unless delimited? (display " " port)))
(display "(" port)
(let* ((new-column (loop column column #t context head))
(indent (if (or (>= new-column max-width)
(not (symbol? head))
(sequence-would-protrude?
(+ new-column 1) tail)
newline?)
column
(+ new-column 1))))
(when newline?
;; Insert a newline right after HEAD.
(newline port)
(display (make-string indent #\space) port))
(let ((column
(print-sequence context indent
(if newline? indent new-column)
tail newline?)))
(display ")" port)
(+ column 1)))))
(_
(let* ((str (cond ((string? obj)
(printed-string obj context))
((integer? obj)
(integer->string obj context))
((symbol? obj)
(symbol->display-string obj context))
(else
(object->string obj))))
(len (string-width str)))
(if (and (> (+ column 1 len) max-width)
(not delimited?))
(begin
(newline port)
(display (make-string indent #\space) port)
(display str port)
(+ indent len))
(begin
(unless delimited? (display " " port))
(display str port)
(+ column (if delimited? 0 1) len))))))))
(define (object->string* obj indent . args)
"Pretty-print OBJ with INDENT columns as the initial indent. ARGS are
passed as-is to 'pretty-print-with-comments'."
(call-with-output-string
(lambda (port)
(apply pretty-print-with-comments port obj
#:indent indent
args))))
(define* (pretty-print-with-comments/splice port lst
#:rest rest)
"Write to PORT the expressions and blanks listed in LST."
(for-each (lambda (exp)
(apply pretty-print-with-comments port exp rest)
(unless (blank? exp)
(newline port)))
lst))
