From daa35c9e4b592f055b42e482fe1398527cfdf90b Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 6 Jun 2019 18:00:10 +0200
Subject: Fix cc link rule matching ambiguity wrt to C/C++ sources

Considering a C header as C++ source was definitely a bad idea.
---
 build2/cc/common.hxx    | 13 +++++++------
 build2/cc/link-rule.cxx |  8 +++++---
 build2/cc/module.cxx    | 28 ++++++++++++++++++----------
 build2/cxx/init.cxx     |  1 -
 4 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/build2/cc/common.hxx b/build2/cc/common.hxx
index 19733cf..3f0f9fb 100644
--- a/build2/cc/common.hxx
+++ b/build2/cc/common.hxx
@@ -13,7 +13,8 @@
 #include <build2/bin/target.hxx>
 
 #include <build2/cc/types.hxx>
-#include <build2/cc/guess.hxx> // compiler_id
+#include <build2/cc/guess.hxx>  // compiler_id
+#include <build2/cc/target.hxx> // h{}
 
 namespace build2
 {
@@ -151,21 +152,21 @@ namespace build2
       const target_type& x_src; // Source target type (c{}, cxx{}).
       const target_type* x_mod; // Module target type (mxx{}), if any.
 
-      // Array of target types that are considered headers. Keep them in the
-      // most likely to appear order with the "real header" first and
-      // terminated with NULL.
+      // Array of target types that are considered the X-language headers
+      // (excluding h{} except for C). Keep them in the most likely to appear
+      // order with the "real header" first and terminated with NULL.
       //
       const target_type* const* x_hdr;
 
       template <typename T>
       bool
-      x_header (const T& t) const
+      x_header (const T& t, bool c_hdr = true) const
       {
         for (const target_type* const* ht (x_hdr); *ht != nullptr; ++ht)
           if (t.is_a (**ht))
             return true;
 
-        return false;
+        return c_hdr && t.is_a (h::static_type);
       }
 
       // Array of target types that can be #include'd. Used to reverse-lookup
diff --git a/build2/cc/link-rule.cxx b/build2/cc/link-rule.cxx
index 372d077..3b58ab7 100644
--- a/build2/cc/link-rule.cxx
+++ b/build2/cc/link-rule.cxx
@@ -87,12 +87,14 @@ namespace build2
 
         if (p.is_a (x_src)                        ||
             (x_mod != nullptr && p.is_a (*x_mod)) ||
-            (lt.library ()    && x_header (p))) // Header-only library.
+            // Header-only X library (or library with C source and X header).
+            (lt.library ()    && x_header (p, false /* c_hdr */)))
         {
           seen_x = seen_x || true;
         }
         else if (p.is_a<c> ()                  ||
-                 (lt.library () && p.is_a<h> ())) // Header-only library.
+                 // Header-only C library.
+                 (lt.library () && p.is_a<h> ()))
         {
           seen_c = seen_c || true;
         }
@@ -132,7 +134,7 @@ namespace build2
         // then we shouldn't try to handle that (it may need to be compiled,
         // etc). But we assume everyone can handle a C header.
         //
-        else if (p.is_a<cc> () && !(x_header (p) || p.is_a<h> ()))
+        else if (p.is_a<cc> () && !(x_header (p, true /* c_hdr */)))
         {
           l4 ([&]{trace << "non-" << x_lang << " prerequisite " << p
                         << " for target " << t;});
diff --git a/build2/cc/module.cxx b/build2/cc/module.cxx
index 7527da2..14d3ceb 100644
--- a/build2/cc/module.cxx
+++ b/build2/cc/module.cxx
@@ -578,24 +578,32 @@ namespace build2
       {
         using namespace install;
 
-        auto& t (rs.target_types);
+        auto& tts (rs.target_types);
 
-        t.insert (x_src);
+        tts.insert (x_src);
 
-        // Note: module (x_mod) is in x_hdr.
-
-        for (const target_type* const* ht (x_hdr); *ht != nullptr; ++ht)
+        auto insert_hdr = [&rs, &tts, install_loaded] (const target_type& tt)
         {
-          t.insert (**ht);
+          tts.insert (tt);
 
           // Install headers into install.include.
           //
           if (install_loaded)
-            install_path (rs, **ht, dir_path ("include"));
-        }
+            install_path (rs, tt, dir_path ("include"));
+        };
+
+        // Note: module (x_mod) is in x_hdr.
+        //
+        for (const target_type* const* ht (x_hdr); *ht != nullptr; ++ht)
+          insert_hdr (**ht);
+
+        // Also register the C header for C-derived languages.
+        //
+        if (*x_hdr != &h::static_type)
+          insert_hdr (h::static_type);
 
-        t.insert<pca> ();
-        t.insert<pcs> ();
+        tts.insert<pca> ();
+        tts.insert<pcs> ();
 
         if (install_loaded)
           install_path<pc> (rs, dir_path ("pkgconfig"));
diff --git a/build2/cxx/init.cxx b/build2/cxx/init.cxx
index ff104d3..92d5da8 100644
--- a/build2/cxx/init.cxx
+++ b/build2/cxx/init.cxx
@@ -526,7 +526,6 @@ namespace build2
     static const target_type* const hdr[] =
     {
       &hxx::static_type,
-      &h::static_type,
       &ixx::static_type,
       &txx::static_type,
       &mxx::static_type,
-- 
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