AC_INIT: better handling of unusual arguments (#110349)

Fix some subtle quotation bugs in _AC_INIT_PACKAGE that made it
impossible to put ‘,’ or an unbalanced close parenthesis in some of
the arguments to AC_INIT.  Document that arguments to AC_INIT
containing parentheses, square brackets, ‘,’ or ‘#’ may need to be
double-quoted.  Provide more detailed examples and exposition re
computing the arguments to AC_INIT when autoconf is run (e.g. with
git-version-gen).  Add a whole bunch more tests for unusual arguments
to AC_INIT, and a test that the backward-compatibility behavior of
AC_INIT with only one argument is still correct.

This may still break some of the existing configure scripts described
in the threads at
https://lists.gnu.org/r/autoconf/2020-10/msg00013.html and
https://lists.gnu.org/r/bug-autoconf/2020-10/msg00012.html
but, I hope, only in ways covered by the existing warning in NEWS
about pickier M4 quotation.

* lib/autoconf/general.m4 (_AC_INIT_PACKAGE): Redo argument
  normalization and default value selection in a simpler, less
  error-prone fashion.
  (_AC_INIT_PACKAGE_N): New helper subroutine.
  (AC_INIT): Always call _AC_INIT_PACKAGE, but supply no arguments if
  we were called with only one argument.

* tests/base.at (AC_INIT (obsolete invocation)): New test.
  (AC_INIT with unusual version strings): Expand test.

* doc/autoconf.texi (AC_INIT): Revise.

3 files changed, 342 insertions, 72 deletions

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index f78e5fc5..5e72add9 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -909,6 +909,9 @@ This module contains a source file for the replacement header, along
 with an Autoconf macro that arranges to use the replacement header on
 old-fashioned systems.
 
+For more information, consult the Gnulib website,
+@uref{https://@/www.gnu.org/@/software/@/gnulib/}.
+
 @node Libtool
 @section Libtool
 
@@ -1877,21 +1880,88 @@ distribution tar ball names (e.g., @samp{autoconf}).  It defaults to
 other than alphanumerics and underscores are changed to @samp{-}.  If
 provided, @var{url} should be the home page for the package.
 
-All the arguments of @code{AC_INIT} must be static, i.e., there should not
-be any shell computation, quotes, or newlines, but they can be computed
-by M4.  This is because the package information strings are expanded at
-M4 time into several contexts, and must give the same text at shell time
-whether used in single-quoted strings, double-quoted strings, quoted
-here-documents, or unquoted here-documents.  It is permissible to use
-@code{m4_esyscmd} or @code{m4_esyscmd_s} for computing a version string
-that changes with every commit to a version control system (in fact,
-Autoconf does just that, for all builds of the development tree made
-between releases).
-
-The @var{tarname} argument is used to construct filenames.
-In addition to being static, it should not contain wildcard
-characters, white space, or anything else that could be troublesome
-as part of a file or directory name.
+Leading and trailing whitespace is stripped from all the arguments to
+@code{AC_INIT}, and interior whitespace is collapsed to a single space.
+This means that, for instance, if you want to put several email
+addresses in @var{bug-report}, you can put each one on its own line:
+
+@smallexample
+@group
+# We keep having problems with the mail hosting for
+# gnomovision.example, so give people an alternative.
+AC_INIT([Gnomovision], [17.0.1], [
+    bugs@@gnomovision.example
+    or gnomo-bugs@@reliable-email.example
+])
+@end group
+@end smallexample
+
+The arguments to @code{AC_INIT} may be computed by M4, when
+@command{autoconf} is run.  For instance, if you want to include the
+package's version number in the @var{tarname}, but you don't want to
+repeat it, you can use a helper macro:
+
+@smallexample
+@group
+m4_define([gnomo_VERSION], [17.0.1])
+AC_INIT([Gnomovision],
+        m4_defn([gnomo_VERSION]),
+        [bugs@@gnomovision.example],
+        [gnomo-]m4_defn([gnomo_VERSION]))
+@end group
+@end smallexample
+
+This uses @code{m4_defn} to produce the expansion of
+@code{gnomo_VERSION} @emph{as a quoted string}, so that if there happen
+to be any more M4 macro names in @code{gnomo_VERSION}, they will not be
+expanded. @xref{Defn,,Renaming Macros,m4,GNU m4 macro processor}.
+
+Continuing this example, if you don't want to embed the version number
+in @file{configure.ac} at all, you can use @code{m4_esyscmd} to look it
+up somewhere else when @command{autoconf} is run:
+
+@smallexample
+@group
+m4_define([gnomo_VERSION],
+  m4_esyscmd([build-aux/git-version-gen .tarball-version]))
+AC_INIT([Gnomovision],
+        m4_defn([gnomo_VERSION]),
+        [bugs@@gnomovision.example],
+        [gnomo-]m4_defn([gnomo_VERSION]))
+@end group
+@end smallexample
+
+This uses the utility script @command{git-version-gen} to look up
+the package's version in its version control metadata.  This script
+is part of Gnulib (@pxref{Gnulib}).
+
+The arguments to @code{AC_INIT} are written into @file{configure} in
+several different places.  Therefore, we strongly recommend that you
+write any M4 logic in @code{AC_INIT} arguments to be evaluated
+@emph{before} @code{AC_INIT} itself is evaluated.  For instance, in the
+above example, the second argument to @code{m4_define} is @emph{not}
+quoted, so the @code{m4_esyscmd} is evaluated only once, and
+@code{gnomo_VERSION} is defined to the output of the command.  If the
+second argument to @code{m4_define} were quoted, @code{m4_esyscmd} would
+be evaluated each time the @var{version} or @var{tarname} arguments were
+written to @file{configure}, and the command would be run repeatedly.
+
+In some of the places where the arguments to @code{AC_INIT} are used,
+within @file{configure}, shell evaluation cannot happen.  Therefore, the
+arguments to @code{AC_INIT} may @emph{not} be computed when
+@command{configure} is run.  If they contain any construct that isn't
+always treated as literal by the shell (e.g.@: variable expansions),
+@command{autoconf} will issue an error.
+
+The @var{tarname} argument is used to construct filenames.  It should
+not contain wildcard characters, white space, or anything else that
+could be troublesome as part of a file or directory name.
+
+Some of M4's active characters (notably parentheses, square brackets,
+@samp{,} and @samp{#}) commonly appear in URLs and lists of email
+addresses.  If any of these characters appear in an argument to AC_INIT,
+that argument will probably need to be double-quoted to avoid errors
+and mistranscriptions.  @xref{M4 Quotation}.
 
 The following M4 macros (e.g., @code{AC_PACKAGE_NAME}), output variables
 (e.g., @code{PACKAGE_NAME}), and preprocessor symbols (e.g.,
diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
index 90cb5a5a..f75b2dbb 100644
--- a/lib/autoconf/general.m4
+++ b/lib/autoconf/general.m4
@@ -230,56 +230,49 @@ m4_define([_AC_INIT_LITERAL],
 
 # _AC_INIT_PACKAGE(PACKAGE-NAME, VERSION, BUG-REPORT, [TARNAME], [URL])
 # ---------------------------------------------------------------------
+# Set the values of AC_PACKAGE_{NAME,VERSION,STRING,BUGREPORT,TARNAME,URL}
+# from the arguments.
 m4_define([_AC_INIT_PACKAGE],
-[m4_pushdef([_ac_init_NAME],     m4_normalize([$1]))
-m4_pushdef([_ac_init_VERSION],   m4_normalize([$2]))
-m4_pushdef([_ac_init_BUGREPORT], m4_normalize([$3]))
-m4_pushdef([_ac_init_TARNAME],   m4_normalize([$4]))
-m4_pushdef([_ac_init_URL],       m4_normalize([$5]))
-# NAME, VERSION, BUGREPORT, and URL should all be safe for use in shell
-# strings of all kinds.
-_AC_INIT_LITERAL(m4_defn([_ac_init_NAME]))
-_AC_INIT_LITERAL(m4_defn([_ac_init_VERSION]))
-_AC_INIT_LITERAL(m4_defn([_ac_init_BUGREPORT]))
-_AC_INIT_LITERAL(m4_defn([_ac_init_URL]))
+[_AC_INIT_PACKAGE_N(m4_normalize([$1]), m4_normalize([$2]), m4_normalize([$3]),
+                    m4_normalize([$4]), m4_normalize([$5]))])
+
+# _AC_INIT_PACKAGE_N(PACKAGE-NAME, VERSION, BUG-REPORT, [TARNAME], [URL])
+# -----------------------------------------------------------------------
+# Subroutine of _AC_INIT_PACKAGE.
+m4_define([_AC_INIT_PACKAGE_N],
+[# PACKAGE-NAME, VERSION, BUGREPORT, and URL should all be safe for use
+# in shell strings of all kinds.
+_AC_INIT_LITERAL([$1])
+_AC_INIT_LITERAL([$2])
+_AC_INIT_LITERAL([$3])
+_AC_INIT_LITERAL([$5])
+
 # TARNAME is even more constrained: it should not contain any shell
 # metacharacters or whitespace, because it is used to construct
 # filenames.
-AS_LITERAL_WORD_IF(m4_defn([_ac_init_TARNAME]), [],
+AS_LITERAL_WORD_IF([$4], [],
   [m4_warn([syntax],
-	   [AC_INIT: unsafe as a filename: "]m4_defn([_ac_init_TARNAME])["])])
-#
-# These do not use m4_copy because we don't want to copy the pushdef stack.
-m4_ifndef([AC_PACKAGE_NAME],
-	  [m4_define([AC_PACKAGE_NAME],
-		     m4_defn([_ac_init_NAME]))])
-m4_ifndef([AC_PACKAGE_VERSION],
-	  [m4_define([AC_PACKAGE_VERSION],
-		     m4_defn([_ac_init_VERSION]))])
-m4_ifndef([AC_PACKAGE_STRING],
-	  [m4_define([AC_PACKAGE_STRING],
-		     m4_defn([_ac_init_NAME])[ ]m4_defn([_ac_init_VERSION]))])
-m4_ifndef([AC_PACKAGE_BUGREPORT],
-	  [m4_define([AC_PACKAGE_BUGREPORT], _ac_init_BUGREPORT)])
-m4_ifndef([AC_PACKAGE_TARNAME],
-	  [m4_define([AC_PACKAGE_TARNAME],
-		     m4_default(m4_defn([_ac_init_TARNAME]),
-				[m4_bpatsubst(m4_tolower(
-				 m4_bpatsubst(m4_defn([_ac_init_NAME]),
-					      [GNU ])),
-				 [[^_abcdefghijklmnopqrstuvwxyz0123456789]],
-				 [-])]))])
-m4_ifndef([AC_PACKAGE_URL],
-	  [m4_define([AC_PACKAGE_URL],
-		     m4_default(m4_defn([_ac_init_URL]),
-				[m4_if(m4_index(m4_defn([_ac_init_NAME]),
-						[GNU ]), [0],
-    [[https://www.gnu.org/software/]m4_defn([AC_PACKAGE_TARNAME])[/]])]))])
-m4_popdef([_ac_init_NAME])
-m4_popdef([_ac_init_VERSION])
-m4_popdef([_ac_init_BUGREPORT])
-m4_popdef([_ac_init_TARNAME])
-m4_popdef([_ac_init_URL])
+	   [AC_INIT: unsafe as a filename: "$4"])])
+
+m4_define_default([AC_PACKAGE_NAME],      [$1])
+m4_define_default([AC_PACKAGE_VERSION],   [$2])
+
+# The m4_strip makes AC_PACKAGE_STRING be [], not [ ], when
+# both $1 and $2 are empty.
+m4_define_default([AC_PACKAGE_STRING],    m4_strip([$1 $2]))
+m4_define_default([AC_PACKAGE_BUGREPORT], [$3])
+
+# N.B. m4_ifnblank strips one layer of quotation from whichever of its
+# second and third argument it evaluates to.
+m4_define_default([AC_PACKAGE_TARNAME],
+  m4_ifnblank([$4], [[$4]],
+    [m4_quote(m4_bpatsubst(m4_tolower(m4_bpatsubst([$1], [^GNU ], [])),
+      [[^_abcdefghijklmnopqrstuvwxyz0123456789]], [-]))]))
+m4_define_default([AC_PACKAGE_URL],
+  m4_ifnblank([$5], [[$5]],
+    [m4_if(m4_index([$1], [GNU ]), [0],
+      [[https://www.gnu.org/software/]m4_defn([AC_PACKAGE_TARNAME])[/]],
+      [])]))
 ])
 
 
@@ -1445,7 +1438,7 @@ m4_define([_AS_FORCE_REEXEC_WITH_CONFIG_SHELL], [yes])
 AS_INIT[]dnl
 AS_PREPARE[]dnl
 m4_divert_push([KILL])
-m4_ifval([$2], [_AC_INIT_PACKAGE($@)])
+m4_ifval([$2], [_AC_INIT_PACKAGE($@)], [_AC_INIT_PACKAGE()])
 _AC_INIT_DEFAULTS
 _AC_INIT_PARSE_ARGS
 _AC_INIT_DIRCHECK
diff --git a/tests/base.at b/tests/base.at
index 2c5c4bdf..45b5142e 100644
--- a/tests/base.at
+++ b/tests/base.at
@@ -231,6 +231,38 @@ AT_CHECK([grep "^PACKAGE_TARNAME='fu'\$" configure], [], [ignore])
 
 AT_CLEANUP
 
+## ------------------------------- ##
+## AC_INIT (obsolete invocation).  ##
+## ------------------------------- ##
+
+# When AC_INIT is called with only one argument, it is equivalent to
+# passing that argument to AC_CONFIG_SRCDIR and then calling AC_INIT
+# with _no_ arguments.  In particular, PACKAGE should _not_ be set
+# to whatever the first argument is.
+
+AT_SETUP([AC_INIT (obsolete invocation)])
+
+AT_DATA([configure.ac],
+[[AC_INIT([program.c])
+AC_OUTPUT
+]])
+
+AT_CHECK_AUTOCONF
+
+# Ensure we get the expected definition:
+AT_CHECK([grep "^PACKAGE_NAME=''\$" configure], [], [ignore])
+
+# Running autoconf right now should fail because program.c doesn't exist.
+AT_CHECK_CONFIGURE([], [1], [],
+[[configure: error: cannot find sources (program.c) in . or ..
+]])
+
+# Create program.c and then it should be fine.
+AT_DATA([program.c])
+AT_CHECK_CONFIGURE
+
+AT_CLEANUP
+
 
 ## ------------------------------------- ##
 ## AC_INIT with unusual version strings. ##
@@ -238,36 +270,136 @@ AT_CLEANUP
 
 AT_SETUP([AC_INIT with unusual version strings])
 
+if echo 'ab*c' | grep -F 'ab*c' >/dev/null 2>&1; then
+  FGREP="grep -F"
+else
+  FGREP=fgrep
+fi
+
+# In both of the arguments that might contain URLs, make sure we test
+# all of the unusual ASCII characters that commonly appear in URLs.
+#
+# The RFC 3986 "unreserved" characters are ASCII letters and digits, plus
+#    - . _ ~
+# The RFC 3986 "gen-delims" and "sub-delims" are
+#    / : ? # [ ] @ ! $ & ' ( ) * + , ; =
+# The URL escape character is
+#    %
+#
+# Any argument that contains characters significant to M4,
+#    [ ] ( ) ,
+# may need to be double-quoted depending on exactly how they are used
+# (as would an argument that contains a macro name, but we don't test
+# that here).
+#
+# Characters that are still significant for Bourne shell within a
+# single-quoted string, double-quoted string, quoted here-doc, or
+# unquoted here-doc are explicitly not allowed:
+#    ' " ` \ $
+#
+# We don't test unbalanced parentheses or brackets here.
+
 AT_DATA([configure.ac],
-[[AC_INIT([GNU String++ with  spaces (foo)],
+[[AC_INIT([GNU String++ with  spaces
+           (foo)],
 	  [2.48++  (2010-07-03)],
-          [[https://example.com/?a=b&c=d#e]],
+          [[https://example/~bug/cdfijknoqrvw/-._:@!()[]*+,;/?y=z#1234567890]],
           [string++],
-          [[https://example.com/?f=g&h=i%2fj#42]])
+          [[HTTPS://EXAMPLE/~PKG/BCDFIJNOQRUVW/-._:@!()[]*+,;/?y=z#1234567890]])
 AC_OUTPUT
 ]])
 
-if echo 'ab*c' | grep -F 'ab*c' >/dev/null 2>&1; then
-  FGREP="grep -F"
-else
-  FGREP=fgrep
-fi
+AT_CHECK_AUTOCONF([-Werror])
+AT_CHECK_CONFIGURE([-q])
+
+AT_CHECK_CONFIGURE([--help], [], [stdout])
+AT_CHECK([[$FGREP \
+  'https://example/~bug/cdfijknoqrvw/-._:@!()[]*+,;/?y=z#1234567890' \
+  stdout]], [], [ignore])
+AT_CHECK([[$FGREP \
+  'HTTPS://EXAMPLE/~PKG/BCDFIJNOQRUVW/-._:@!()[]*+,;/?y=z#1234567890' \
+  stdout]], [], [ignore])
+
+AT_CHECK_CONFIGURE([--version], [], [stdout])
+AT_CHECK([$FGREP 'GNU String++ with spaces (foo)' stdout], [], [ignore])
+AT_CHECK([$FGREP '2.48++ (2010-07-03)' stdout], [], [ignore])
+
+AT_CHECK([./config.status --help], [], [stdout])
+AT_CHECK([[$FGREP \
+  'https://example/~bug/cdfijknoqrvw/-._:@!()[]*+,;/?y=z#1234567890' \
+  stdout]], [], [ignore])
+AT_CHECK([[$FGREP \
+  'HTTPS://EXAMPLE/~PKG/BCDFIJNOQRUVW/-._:@!()[]*+,;/?y=z#1234567890' \
+  stdout]], [], [ignore])
+
+AT_CHECK([./config.status --version], [], [stdout])
+AT_CHECK([$FGREP 'GNU String++ with spaces (foo)' stdout], [], [ignore])
+AT_CHECK([$FGREP '2.48++ (2010-07-03)' stdout], [], [ignore])
+
+# Repeat the above test using all the unusual characters that might appear
+# in a list of email addresses in both BUG-REPORT and URL.  (URL isn't
+# supposed to contain email addresses, but there's no good reason to
+# restrict its syntax.)
+# The RFC 5822 "atext" characters are ASCII letters and digits, plus
+#    ! # $ % & ' * + - / = ? ^ _ ` { | } ~
+# The RFC 5822 "special" characters, all of which might appear somewhere
+# in an address list, are
+#    ( ) < > [ ] : ; @ \ , . "
+# As above, characters that are significant for Bourne shell within
+# strings and heredocs are explicitly not allowed:
+#    ' " ` \ $
+# As above, any argument that contains characters significant to M4,
+#    [ ] ( ) ,
+# may need to be double-quoted depending on exactly how they are used
+# (as would an argument that contains a macro name, but we don't test
+# that here).
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String++ with  spaces
+           (foo)],
+	  [2.48++  (2010-07-03)],
+          [[bugs: fred <A=B?C^D_E@F>,
+                  G!H!I#J@K.L (wilma),
+                  M%N&O@[156.247.38.49],
+                  P*Q+R-S/T@U,
+                  {jon|chyp~}@kqtvxz.VWXYZ;]],
+          [string++],
+          [[contact: jem <A=B?C^D_E@bd>,
+                     F!G!H#I@fv.J (lugh),
+                     K%L&M@[156.247.38.49],
+                     N*O+P-Q/R@STU,
+                     {qik|~prys}@wxz.VWXYZ;]])
+AC_OUTPUT
+]])
 
 AT_CHECK_AUTOCONF([-Werror])
 AT_CHECK_CONFIGURE([-q])
+
 AT_CHECK_CONFIGURE([--help], [], [stdout])
-AT_CHECK([[$FGREP 'com/?a=b&c=d#e' stdout]], [], [ignore])
-AT_CHECK([[$FGREP 'com/?f=g&h=i%2fj#42' stdout]], [], [ignore])
+AT_CHECK([[$FGREP \
+  'bugs: fred <A=B?C^D_E@F>, G!H!I#J@K.L (wilma), M%N&O@[156.247.38.49], P*Q+R-S/T@U, {jon|chyp~}@kqtvxz.VWXYZ;' \
+  stdout]], [], [ignore])
+AT_CHECK([[$FGREP \
+  'contact: jem <A=B?C^D_E@bd>, F!G!H#I@fv.J (lugh), K%L&M@[156.247.38.49], N*O+P-Q/R@STU, {qik|~prys}@wxz.VWXYZ;' \
+  stdout]], [], [ignore])
+
 AT_CHECK_CONFIGURE([--version], [], [stdout])
 AT_CHECK([$FGREP 'GNU String++ with spaces (foo)' stdout], [], [ignore])
 AT_CHECK([$FGREP '2.48++ (2010-07-03)' stdout], [], [ignore])
 
 AT_CHECK([./config.status --help], [], [stdout])
-AT_CHECK([[$FGREP 'com/?a=b&c=d#e' stdout]], [], [ignore])
+AT_CHECK([[$FGREP \
+  'bugs: fred <A=B?C^D_E@F>, G!H!I#J@K.L (wilma), M%N&O@[156.247.38.49], P*Q+R-S/T@U, {jon|chyp~}@kqtvxz.VWXYZ;' \
+  stdout]], [], [ignore])
+AT_CHECK([[$FGREP \
+  'contact: jem <A=B?C^D_E@bd>, F!G!H#I@fv.J (lugh), K%L&M@[156.247.38.49], N*O+P-Q/R@STU, {qik|~prys}@wxz.VWXYZ;' \
+  stdout]], [], [ignore])
+
 AT_CHECK([./config.status --version], [], [stdout])
 AT_CHECK([$FGREP 'GNU String++ with spaces (foo)' stdout], [], [ignore])
 AT_CHECK([$FGREP '2.48++ (2010-07-03)' stdout], [], [ignore])
 
+# Check for invalid characters in each argument.
 AT_DATA([configure.ac],
 [[AC_INIT([GNU "String++"],
 	  [2.48], [https://example.com/], [string++])
@@ -347,6 +479,81 @@ AC_OUTPUT
 AT_CHECK_AUTOCONF([-Werror], [1], [ignore], [stderr])
 AT_CHECK([grep 'AC_INIT: unsafe as a filename: ' stderr], [], [ignore])
 
+# Commas and unbalanced close parentheses are especially troublesome for M4.
+# They are only expected to work when double-quoted, but even then they can
+# cause malfunctions if not handled carefully within Autoconf.
+
+AT_DATA([configure.ac],
+[[AC_INIT([[GNU, String]], [2.48], [bugs@gstring.example],
+          [string], [https://gstring.example/])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
+
+AT_DATA([configure.ac],
+[[AC_INIT([[GNU String)]], [2.48], [bugs@gstring.example],
+          [string], [https://gstring.example/])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String], [[2,48]], [bugs@gstring.example],
+          [string], [https://gstring.example/])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String], [[2.48)]], [bugs@gstring.example],
+          [string], [https://gstring.example/])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String], [2.48], [[bugs@gstring.example,
+                                 gstring-bugs@example.com]],
+          [string], [https://gstring.example/])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String], [2.48], [[bugs)@gstring.example]],
+          [string], [https://gstring.example/])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String], [2.48], [bugs@gstring.example],
+          [[string,]], [https://gstring.example/])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String], [2.48], [bugs@gstring.example],
+          [[string)]], [https://gstring.example/])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF([], [0], [ignore], [stderr])
+AT_CHECK([grep 'AC_INIT: unsafe as a filename: ' stderr], [], [ignore])
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String], [2.48], [bugs@gstring.example],
+          [string], [[https://gstring.example/docs,html]])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
+
+AT_DATA([configure.ac],
+[[AC_INIT([GNU String], [2.48], [bugs@gstring.example],
+          [string], [[https://gstring.example/weird)/path]])
+AC_OUTPUT
+]])
+AT_CHECK_AUTOCONF
 
 AT_CLEANUP