From e17365cb6d1af6ae12fdaaf97f28a02c7ee61bed Mon Sep 17 00:00:00 2001
From: Oliver Reiche <oliver.reiche@huawei.com>
Date: Mon, 7 Aug 2023 15:14:46 +0200
Subject: rules: Support BUILD_ARCH for CC defaults

---
 rules/CC/RULES                |  7 +++++--
 rules/transitions/EXPRESSIONS | 25 +++++++++++++++++--------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/rules/CC/RULES b/rules/CC/RULES
index 33b8520e..c30aaee1 100644
--- a/rules/CC/RULES
+++ b/rules/CC/RULES
@@ -26,7 +26,10 @@
       [ "Optional toolchain directory. A collection of artifacts that provide"
       , "the tools CC, CXX, and AR (if needed). Note that only artifacts of"
       , "the specified targets are considered (no runfiles etc.). Specifying"
-      , "this field extends artifacts from \"base\"."
+      , "this field extends artifacts from \"base\". If the toolchain"
+      , "supports cross-compilation, it should perform a dispatch on the"
+      , "configuration variable \"BUILD_ARCH\" to determine for which"
+      , "architecture to generate code for."
       ]
     , "deps":
       [ "Optional CC libraries any CC library and CC binary implicitly depend"
@@ -69,7 +72,7 @@
       , "with \":\". Specifying this field extends values from \"base\"."
       ]
     }
-  , "config_vars": ["ARCH", "HOST_ARCH"]
+  , "config_vars": ["ARCH", "HOST_ARCH", "TARGET_ARCH"]
   , "imports":
     { "base-provides": "defaults-base-provides"
     , "base-provides-list": "defaults-base-provides-list"
diff --git a/rules/transitions/EXPRESSIONS b/rules/transitions/EXPRESSIONS
index 4fd0d1e9..596b20ef 100644
--- a/rules/transitions/EXPRESSIONS
+++ b/rules/transitions/EXPRESSIONS
@@ -1,13 +1,22 @@
 { "for host":
-  { "vars": ["ARCH", "HOST_ARCH"]
+  { "vars": ["ARCH", "HOST_ARCH", "TARGET_ARCH"]
   , "expression":
-    { "type": "singleton_map"
-    , "key": "TARGET_ARCH"
-    , "value":
-      { "type": "var"
-      , "name": "HOST_ARCH"
-      , "default": {"type": "var", "name": "ARCH"}
-      }
+    { "type": "let*"
+    , "bindings":
+      [ [ "BUILD_ARCH"
+        , { "type": "var"
+          , "name": "TARGET_ARCH"
+          , "default": {"type": "var", "name": "ARCH"}
+          }
+        ]
+      , [ "TARGET_ARCH"
+        , { "type": "var"
+          , "name": "HOST_ARCH"
+          , "default": {"type": "var", "name": "ARCH"}
+          }
+        ]
+      ]
+    , "body": {"type": "env", "vars": ["BUILD_ARCH", "TARGET_ARCH"]}
     }
   }
 , "target properties":
-- 
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