Make "config" accept a computed target

... and thus allowing the "business logic" in the configuration
target (e.g., setting defaults and derived options) to be shared
by many targets.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/buildtool/build_engine/target_map/built_in_rules.cpp b/src/buildtool/build_engine/target_map/built_in_rules.cpp
index a34dfb03..763385e2 100644
--- a/src/buildtool/build_engine/target_map/built_in_rules.cpp
+++ b/src/buildtool/build_engine/target_map/built_in_rules.cpp
@@ -953,7 +953,16 @@ void ConfigureRule(
     }
     auto param_config = key.config.Prune(*param_vars);
 
-    auto configured_target_name = desc->ReadExpression("target");
+    auto configured_target_name_exp = desc->ReadExpression("target");
+    if (not configured_target_name_exp) {
+        return;
+    }
+    auto configured_target_name = configured_target_name_exp.Evaluate(
+        param_config, {}, [logger](std::string const& msg) {
+            (*logger)(
+                fmt::format("Evaluating 'target' failed with error:\n{}", msg),
+                true);
+        });
     if (not configured_target_name) {
         return;
     }