Tighten cc rules matching

Specifically, make sure the rule does not match if there is a c-common
prerequisites that it doesn't recognize.

4 files changed, 21 insertions, 15 deletions

diff --git a/build2/cc/common.hxx b/build2/cc/common.hxx
index dccf62e..e1b04d7 100644
--- a/build2/cc/common.hxx
+++ b/build2/cc/common.hxx
@@ -148,7 +148,7 @@ namespace build2
       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 "header header" first and
+      // most likely to appear order with the "real header" first and
       // terminated with NULL.
       //
       const target_type* const* x_hdr;
diff --git a/build2/cc/link-rule.cxx b/build2/cc/link-rule.cxx
index c24655a..b7ecd85 100644
--- a/build2/cc/link-rule.cxx
+++ b/build2/cc/link-rule.cxx
@@ -71,7 +71,8 @@ namespace build2
       }
 
       // Scan prerequisites and see if we can work with what we've got. Note
-      // that X could be C. We handle this by always checking for X first.
+      // that X could be C (as in language). We handle this by always checking
+      // for X first.
       //
       // Note also that we treat bmi{} as obj{}.
       //
@@ -84,9 +85,9 @@ namespace build2
         if (include (a, t, p) != include_type::normal)
           continue;
 
-        if (p.is_a (x_src)                           ||
-            (lt.library ()    && p.is_a (*x_hdr[0])) || // Header-only library.
-            (x_mod != nullptr && p.is_a (*x_mod)))
+        if (p.is_a (x_src)                        ||
+            (x_mod != nullptr && p.is_a (*x_mod)) ||
+            (lt.library ()    && x_header (p))) // Header-only library.
         {
           seen_x = seen_x || true;
         }
@@ -127,11 +128,16 @@ namespace build2
         {
           seen_lib = seen_lib || true;
         }
-        // If this is some other c-common source (say C++ in a C rule), then
-        // it will most definitely need to be compiled but we can't do that.
+        // If this is some other c-common header/source (say C++ in a C rule),
+        // 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> ())
+        else if (p.is_a<cc> () && !p.is_a<h> ())
+        {
+          l4 ([&]{trace << "non-" << x_lang << " prerequisite " << p
+                        << " for target " << t;});
           return false;
+        }
       }
 
       if (!(seen_x || seen_c || seen_obj || seen_lib))
diff --git a/build2/cc/target.cxx b/build2/cc/target.cxx
index 7039728..981f4d7 100644
--- a/build2/cc/target.cxx
+++ b/build2/cc/target.cxx
@@ -30,7 +30,7 @@ namespace build2
     const target_type h::static_type
     {
       "h",
-      &file::static_type,
+      &cc::static_type,
       &target_factory<h>,
       nullptr, /* fixed_extension */
       &target_extension_var<var_extension, h_ext_def>,
diff --git a/build2/cc/target.hxx b/build2/cc/target.hxx
index 4fb38cb..395c233 100644
--- a/build2/cc/target.hxx
+++ b/build2/cc/target.hxx
@@ -14,10 +14,10 @@ namespace build2
 {
   namespace cc
   {
-    // This is an abstract base target for all c-common source files. We use
-    // this arrangement in rule matching to detect "unknown" (to this rule)
-    // source files that it cannot handle but should not ignore either. For
-    // example, a C link rule that sees a C++ source file.
+    // This is an abstract base target for all c-common header/source files.
+    // We use this arrangement during rule matching to detect "unknown" (to
+    // this rule) source/header files that it cannot handle but should not
+    // ignore either. For example, a C link rule that sees a C++ source file.
     //
     class cc: public file
     {
@@ -32,10 +32,10 @@ namespace build2
     // There is hardly a c-family compilation without a C header inclusion.
     // As a result, this target type is registered for any c-family module.
     //
-    class h: public file
+    class h: public cc
     {
     public:
-      using file::file;
+      using cc::cc;
 
     public:
       static const target_type static_type;