Add in{} target type for .in ("input") file (requires preprocessing)

3 files changed, 77 insertions, 0 deletions

diff --git a/build2/context.cxx b/build2/context.cxx
index 40537b4..97a2995 100644
--- a/build2/context.cxx
+++ b/build2/context.cxx
@@ -345,6 +345,7 @@ namespace build2
       t.insert<alias> ();
       t.insert<dir>   ();
       t.insert<fsdir> ();
+      t.insert<in>    ();
       t.insert<exe>   ();
       t.insert<doc>   ();
       t.insert<man>   ();
diff --git a/build2/target b/build2/target
index c672dc9..1a1fd8d 100644
--- a/build2/target
+++ b/build2/target
@@ -1428,6 +1428,12 @@ namespace build2
       return const_cast<path_target*> (this)->derive_path (); // MT-aware.
     }
 
+    const string&
+    derive_extension () const
+    {
+      return const_cast<path_target*> (this)->derive_extension (); // MT-aware.
+    }
+
   public:
     static const target_type static_type;
 
@@ -1526,6 +1532,33 @@ namespace build2
     virtual const target_type& dynamic_type () const {return static_type;}
   };
 
+  // This is the venerable .in ("input") file that needs some kind of
+  // preprocessing.
+  //
+  // One interesting aspect of this target type is that the prerequisite
+  // search is target-dependent. Consider:
+  //
+  // hxx{version}: in{version.hxx} // version.hxx.in -> version.hxx
+  //
+  // Having to specify the header extension explicitly is inelegant. Instead
+  // what we really want to write is this:
+  //
+  // hxx{version}: in{version}
+  //
+  // But how do we know that in{version} means version.hxx.in? That's where
+  // the target-dependent search comes in: we take into account the target
+  // we are a prerequisite of.
+  //
+  class in: public file
+  {
+  public:
+    using file::file;
+
+  public:
+    static const target_type static_type;
+    virtual const target_type& dynamic_type () const {return static_type;}
+  };
+
   // Common documentation file targets.
   //
   // @@ Maybe these should be in the built-in doc module?
diff --git a/build2/target.cxx b/build2/target.cxx
index e0f4e55..e1712b9 100644
--- a/build2/target.cxx
+++ b/build2/target.cxx
@@ -1008,6 +1008,49 @@ namespace build2
     false
   };
 
+  // in
+  //
+  static const target*
+  in_search (const target& xt, const prerequisite_key& cpk)
+  {
+    // If we have no extension then derive it from our target. The delegate
+    // to file_search().
+    //
+    prerequisite_key pk (cpk);
+    optional<string>& e (pk.tk.ext);
+
+    if (!e)
+    {
+      if (const file* t = xt.is_a<file> ())
+      {
+        const string& te (t->derive_extension ());
+        e = te + (te.empty () ? "" : ".") + "in";
+      }
+      else
+        fail << "prerequisite " << pk << " for a non-file target " << xt;
+    }
+
+    return file_search (xt, pk);
+  }
+
+  static bool
+  in_pattern (const target_type&, const scope&, string&, bool)
+  {
+    fail << "pattern in in{} prerequisite" << endf;
+  }
+
+  const target_type in::static_type
+  {
+    "in",
+    &file::static_type,
+    &file_factory<in, file_ext_def>, // No extension by default.
+    &target_extension_assert,        // Should be taken care by search.
+    &in_pattern,
+    &target_print_1_ext_verb,        // Same as file.
+    &in_search,
+    false
+  };
+
   const target_type doc::static_type
   {
     "doc",