From 626bd6434662436423d0c5cd9689149076ebed07 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 22 Feb 2024 09:28:16 +0200
Subject: Detect non-cc::link_rule libraries not marked with cc.type=cc

Fixes GH issue #368.
---
 libbuild2/cc/link-rule.cxx | 15 +++++++++++----
 libbuild2/target.hxx       | 27 +++++++++++++++++++++++++--
 2 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/libbuild2/cc/link-rule.cxx b/libbuild2/cc/link-rule.cxx
index d705eb5..704fb47 100644
--- a/libbuild2/cc/link-rule.cxx
+++ b/libbuild2/cc/link-rule.cxx
@@ -2261,14 +2261,21 @@ namespace build2
                    *type != "cc" &&
                    type->compare (0, 3, "cc,") != 0)
           {
-            auto& md (l->data<link_rule::match_data> (d.a));
-            assert (md.for_install); // Must have been executed.
+            auto* md (l->try_data<link_rule::match_data> (d.a));
+
+            if (md == nullptr)
+              fail << "library " << *l << " is not built with cc module-based "
+                   << "link rule" <<
+                info << "mark it as generic with cc.type=cc target-specific "
+                     << "variable";
+
+            assert (md->for_install); // Must have been executed.
 
             // The user will get the target name from the context info.
             //
-            if (*md.for_install != *d.for_install)
+            if (*md->for_install != *d.for_install)
               fail << "incompatible " << *l << " build" <<
-                info << "library is built " << (*md.for_install ? "" : "not ")
+                info << "library is built " << (*md->for_install ? "" : "not ")
                      << "for install";
           }
 
diff --git a/libbuild2/target.hxx b/libbuild2/target.hxx
index 0d4eece..20cd32d 100644
--- a/libbuild2/target.hxx
+++ b/libbuild2/target.hxx
@@ -1219,13 +1219,28 @@ namespace build2
     }
 
     template <typename T>
-    typename std::enable_if<!data_invocable<T>::value, T&>::type&
+    typename std::enable_if<!data_invocable<T>::value, T&>::type
     data (action a) const
     {
       using V = typename std::remove_cv<T>::type;
       return state[a].recipe.target<data_wrapper<V>> ()->d;
     }
 
+    // Return NULL if there is no data or the data is of a different type.
+    //
+    template <typename T>
+    typename std::enable_if<!data_invocable<T>::value, T*>::type
+    try_data (action a) const
+    {
+      using V = typename std::remove_cv<T>::type;
+
+      if (auto& r = state[a].recipe)
+        if (auto* t = r.target<data_wrapper<V>> ())
+          return &t->d;
+
+      return nullptr;
+    }
+
     // Note that in this case we don't strip const (the expectation is that we
     // move the recipe in/out of data).
     //
@@ -1250,12 +1265,20 @@ namespace build2
     }
 
     template <typename T>
-    typename std::enable_if<data_invocable<T>::value, T&>::type&
+    typename std::enable_if<data_invocable<T>::value, T&>::type
     data (action a) const
     {
       return *state[a].recipe.target<T> ();
     }
 
+    template <typename T>
+    typename std::enable_if<data_invocable<T>::value, T*>::type
+    try_data (action a) const
+    {
+      auto& r = state[a].recipe;
+      return r ? r.target<T> () : nullptr;
+    }
+
     // Target type info and casting.
     //
   public:
-- 
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