Add support for module interface-only libraries

Also suppress generation of the object file in cases where we don't need it.

3 files changed, 27 insertions, 12 deletions

diff --git a/libbuild2/bin/init.cxx b/libbuild2/bin/init.cxx
index 9c16432..49ba518 100644
--- a/libbuild2/bin/init.cxx
+++ b/libbuild2/bin/init.cxx
@@ -116,12 +116,23 @@ namespace build2
       //
       // If unspecified, defaults to false for liba{} and to true for libu*{}.
       //
-      vp.insert<bool>      ("bin.whole", variable_visibility::target);
+      vp.insert<bool> ("bin.whole", variable_visibility::target);
 
-      vp.insert<string>    ("bin.exe.prefix");
-      vp.insert<string>    ("bin.exe.suffix");
-      vp.insert<string>    ("bin.lib.prefix");
-      vp.insert<string>    ("bin.lib.suffix");
+      // Mark library as binless.
+      //
+      // For example, the user can mark a C++ library consisting of only
+      // module interfaces as binless so it becomes a modules equivalent to
+      // header-only library (which we will call a module interface-only
+      // library).
+      //
+      vp.insert<bool> ("bin.binless", variable_visibility::target);
+
+      // Executable and library name prefixes and suffixes.
+      //
+      vp.insert<string> ("bin.exe.prefix");
+      vp.insert<string> ("bin.exe.suffix");
+      vp.insert<string> ("bin.lib.prefix");
+      vp.insert<string> ("bin.lib.suffix");
 
       // The optional custom clean patterns should be just the pattern stem,
       // without the library prefix/name or extension. For example, `-[A-Z]`
diff --git a/libbuild2/bin/utility.cxx b/libbuild2/bin/utility.cxx
index 6b0c4de..11230cd 100644
--- a/libbuild2/bin/utility.cxx
+++ b/libbuild2/bin/utility.cxx
@@ -47,9 +47,11 @@ namespace build2
       return lmembers {a, s};
     }
 
-    const target*
+    const file*
     link_member (const libx& x, action a, linfo li, bool exist)
     {
+      const target* r;
+
       if (x.is_a<libul> ())
       {
         // For libul{} that is linked to an executable the member choice
@@ -72,7 +74,7 @@ namespace build2
 
         // Called by the compile rule during execute.
         //
-        return x.ctx.phase == run_phase::match && !exist
+        r = x.ctx.phase == run_phase::match && !exist
           ? &search (x, tt, x.dir, x.out, x.name)
           : search_existing (x.ctx, tt, x.dir, x.out, x.name);
       }
@@ -87,15 +89,17 @@ namespace build2
         group_view gv (resolve_members (a, l));
         assert (gv.members != nullptr);
 
-        pair<otype, bool> r (
+        pair<otype, bool> p (
           link_member (lmembers {l.a != nullptr, l.s != nullptr}, li.order));
 
-        if (!r.second)
-          fail << (r.first == otype::s ? "shared" : "static")
+        if (!p.second)
+          fail << (p.first == otype::s ? "shared" : "static")
                << " variant of " << l << " is not available";
 
-        return r.first == otype::s ? static_cast<const target*> (l.s) : l.a;
+        r = p.first == otype::s ? static_cast<const target*> (l.s) : l.a;
       }
+
+      return static_cast<const file*> (r);
     }
 
     pattern_paths
diff --git a/libbuild2/bin/utility.hxx b/libbuild2/bin/utility.hxx
index 5d7eed4..e12bb5f 100644
--- a/libbuild2/bin/utility.hxx
+++ b/libbuild2/bin/utility.hxx
@@ -59,7 +59,7 @@ namespace build2
     // If existing is true, then only return the member target if it exists
     // (currently only used and supported for utility libraries).
     //
-    LIBBUILD2_BIN_SYMEXPORT const target*
+    LIBBUILD2_BIN_SYMEXPORT const file*
     link_member (const libx&, action, linfo, bool existing = false);
 
     // As above but return otype::a or otype::s as well as an indication if