From c2fb64201b75b6af7ddae9a3e6409a8fc0e46343 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Branimir=20Karad=C5=BEi=C4=87?= <branimirkaradzic@gmail.com>
Date: Wed, 22 Jul 2026 21:46:00 -0700
Subject: [PATCH] fcpp: Fixed expansion for ## operands, and enable
 FPPTAG_RIGHTCONCAT. Closes #3629." (#3842)

---
 3rdparty/fcpp/cpp4.c      |  4 ++--
 3rdparty/fcpp/cpp6.c      | 10 +++++-----
 tools/shaderc/shaderc.cpp |  4 ++++
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/3rdparty/fcpp/cpp4.c b/3rdparty/fcpp/cpp4.c
index a3257b3e9..1d0caaa02 100644
--- a/3rdparty/fcpp/cpp4.c
+++ b/3rdparty/fcpp/cpp4.c
@@ -144,8 +144,8 @@ ReturnCode fpp_dodefine(struct Global *global)
       }
       while (global->workp > global->work && type[(unsigned)*(global->workp - 1)] == SPA)
         --global->workp;                /* Erase leading spaces */
-//       if ((ret=save(global, TOK_SEP)))  /* Stuff a delimiter    */
-//         return(ret);
+      if ((ret=fpp_save(global, TOK_SEP)))  /* Stuff a delimiter    */
+        return(ret);
       c = fpp_skipws(global);               /* Eat whitespace       */
       continue;
     }
diff --git a/3rdparty/fcpp/cpp6.c b/3rdparty/fcpp/cpp6.c
index bb1de15b8..3473c7bc3 100644
--- a/3rdparty/fcpp/cpp6.c
+++ b/3rdparty/fcpp/cpp6.c
@@ -225,13 +225,13 @@ int fpp_catenate(struct Global *global, int lhs_number, ReturnCode *ret)
     }
     c= fpp_get(global);
     if(global->rightconcat) {
-      *ret=fpp_macroid(global, &c);           /* Scan next token      */
+      *ret=fpp_macroid(global, &c);           /* Scan and expand next token */
       if(*ret)
         return(FPP_FALSE);
-    } /* BK - BUG? Parses token into global->tokenbuf but never uses it.
-      else
-      fpp_lookid(global, c);
-      */
+    }
+    else if(type[c] == LET) {
+      fpp_lookid(global, c);                  /* Scan next token into tokenbuf */
+    }
     switch(type[c]) {                   /* What was it?         */
     case LET:                           /* An identifier, ...   */
       if ((int)strlen(token1) + (int)strlen(global->tokenbuf) >= NWORK) {
diff --git a/tools/shaderc/shaderc.cpp b/tools/shaderc/shaderc.cpp
index e59708d48..51da8047b 100644
--- a/tools/shaderc/shaderc.cpp
+++ b/tools/shaderc/shaderc.cpp
@@ -916,6 +916,10 @@ namespace bgfx
 			m_tagptr->data = (void*)0;
 			m_tagptr++;
 
+			m_tagptr->tag = FPPTAG_RIGHTCONCAT;
+			m_tagptr->data = (void*)1;
+			m_tagptr++;
+
 			m_tagptr->tag = FPPTAG_INPUT_NAME;
 			m_tagptr->data = scratch(_filePath);
 			m_tagptr++;