From f2089be3d179afc9b33ca62085c7a0566af7715e Mon Sep 17 00:00:00 2001
From: Pierre Neidhardt <mail@ambrevar.xyz>
Date: Thu, 7 Jan 2021 14:19:44 +0100
Subject: [PATCH] gnu: json-modern-cxx: Install json_fwd.hpp header.

* gnu/packages/cpp.scm (json-modern-cxx)[arguments]: Set
JSON_MultipleHeaders=ON to install optional header.
---
 gnu/packages/cpp.scm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gnu/packages/cpp.scm b/gnu/packages/cpp.scm
index 00e006928e..45d3faeafb 100644
--- a/gnu/packages/cpp.scm
+++ b/gnu/packages/cpp.scm
@@ -334,7 +334,8 @@ (define-public json-modern-cxx
     (build-system cmake-build-system)
     (arguments
      '(#:configure-flags
-       (list (string-append "-DJSON_TestDataDirectory="
+       (list "-DJSON_MultipleHeaders=ON" ; For json_fwd.hpp.
+             (string-append "-DJSON_TestDataDirectory="
                             (assoc-ref %build-inputs "json_test_data")))
        #:phases (modify-phases %standard-phases
                   ;; XXX: When tests are enabled, the install phase will cause