Generate an OCaml quoted string ID in configure

The string @QS@ is available to use in template.in files that produce
OCaml code allowing strings to be written as
{@QS@|@variable_from_configure@|@QS@} guaranteeing that any value of
@variable_from_configure@ yields a properly quoted OCaml string.

The calculation inserts 'o' characters until none of the strings passed
to AC_SUBST include the sequence |o..o}

3 files changed, 53 insertions, 0 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index 7bf3b2df1d..c79ad310b0 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -509,3 +509,27 @@ int main (void) {
       [AC_MSG_RESULT([cross-compiling; assume yes])
       AC_DEFINE([HAS_WORKING_FMA])])])
 ])
+
+# Computes a suitable id to insert in quoted strings to ensure that all OCaml
+# quoted strings generated by configure cannot be "escaped". The ID takes the
+# form {o*|string|o*}.
+AC_DEFUN([OCAML_QUOTED_STRING_ID], [
+  # Go through ac_subst_vars and put all the values to be substituted in
+  # $all_values.
+  QS=''
+  all_values=''
+  for name in $ac_subst_vars; do
+    eval "value=\$${name}"
+    all_values="$all_values $value"
+  done
+
+  # Keep adding 'o' to $QS until |$QS} doesn't appear in any substitution.
+  test_string=''
+  while test "x${test_string}" != "x${all_values}"; do
+    test_string="$all_values"
+    eval "test_string=\"\${test_string##*\|${QS}\}}\""
+    if test "x${test_string}" != "x${all_values}"; then
+      QS="o${QS}"
+    fi
+  done
+])
diff --git a/configure b/configure
index b10c10c38c..61033a8c15 100755
--- a/configure
+++ b/configure
@@ -750,6 +750,7 @@ build_os
 build_vendor
 build_cpu
 build
+QS
 force_instrumented_runtime
 compute_deps
 stdlib_manpages
@@ -2957,6 +2958,7 @@ OCAML_VERSION_SHORT=5.0
 
 
 
+
 ## Generated files
 
 ac_config_files="$ac_config_files Makefile.build_config"
@@ -2994,6 +2996,9 @@ $as_echo "#define OCAML_VERSION 50000" >>confdefs.h
 $as_echo "#define OCAML_VERSION_STRING \"5.0.0+dev0-2021-11-05\"" >>confdefs.h
 
 
+# Works out how many "o"s are needed in quoted strings
+
+
 # Checks for system types
 
 # Make sure we can run config.sub.
@@ -18195,6 +18200,26 @@ LTLIBOBJS=$ac_ltlibobjs
 
 
 
+  # Go through ac_subst_vars and put all the values to be substituted in
+  # $all_values.
+  QS=''
+  all_values=''
+  for name in $ac_subst_vars; do
+    eval "value=\$${name}"
+    all_values="$all_values $value"
+  done
+
+  # Keep adding 'o' to $QS until |$QS} doesn't appear in any substitution.
+  test_string=''
+  while test "x${test_string}" != "x${all_values}"; do
+    test_string="$all_values"
+    eval "test_string=\"\${test_string##*\|${QS}\}}\""
+    if test "x${test_string}" != "x${all_values}"; then
+      QS="o${QS}"
+    fi
+  done
+
+
   # Construct $mkexe
   mkexe="$mkexe_cmd"
   if test -n "$mkexe_cflags"; then :
diff --git a/configure.ac b/configure.ac
index 9c8a506b3f..b3a5df487b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -169,6 +169,7 @@ AC_SUBST([PACKLD])
 AC_SUBST([stdlib_manpages])
 AC_SUBST([compute_deps])
 AC_SUBST([force_instrumented_runtime])
+AC_SUBST([QS])
 
 ## Generated files
 
@@ -192,6 +193,9 @@ m4_if([OCAML__VERSION_EXTRA],[], [],
 AC_DEFINE([OCAML_VERSION], [OCAML__VERSION_NUMBER])
 AC_DEFINE([OCAML_VERSION_STRING], ["][OCAML__VERSION]["])
 
+# Works out how many "o"s are needed in quoted strings
+AC_CONFIG_COMMANDS_PRE(OCAML_QUOTED_STRING_ID)
+
 # Checks for system types
 
 AC_CANONICAL_BUILD