Implement implied buildfile support

In essence, if the buildfile is:

./: */

Then it can be omitted entirely (provided there is at least one subdirectory).

14 files changed, 121 insertions, 55 deletions

diff --git a/build2/b.cxx b/build2/b.cxx
index 15ace65..b13300e 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -911,16 +911,31 @@ main (int argc, char* argv[])
               trace << "  amalgamat: " << cast<dir_path> (l);
           }
 
+          path bf;
           const path& bfn (ops.buildfile ());
-          path bf (bfn.string () != "-" ? src_base / bfn : bfn);
 
-          // If we were guessing src_base, check that the buildfile
-          // exists and if not, issue more detailed diagnostics.
-          //
-          if (guessing && bf.string () != "-" && !exists (bf))
-            fail << bf << " does not exist"
-                 << info << "consider explicitly specifying src_base "
-                 << "for " << tn;
+          if (bfn.string () != "-")
+          {
+            bf = src_base / bfn;
+
+            if (!exists (bf))
+            {
+              // If we were guessing src_base then don't try any implied
+              // buildfile tricks.
+              //
+              if (guessing)
+                fail << bf << " does not exist" <<
+                  info << "consider explicitly specifying src_base for " << tn;
+
+              // If the target is a directory and src_base exists, then assume
+              // implied buildfile; see dir::search_implied().
+              //
+              if ((tn.directory () || tn.type == "dir") && exists (src_base))
+                bf.clear ();
+            }
+          }
+          else
+            bf = bfn;
 
           // Enter project-wide (as opposed to global) variable overrides.
           //
@@ -1040,7 +1055,10 @@ main (int argc, char* argv[])
                           ? out_src (d, rs)
                           : dir_path ());
 
-            mif->search (rs, target_key {ti, &d, &out, &tn.value, e}, l, tgs);
+            mif->search (rs, bs,
+                         target_key {ti, &d, &out, &tn.value, e},
+                         l,
+                         tgs);
           }
         } // target
 
diff --git a/build2/config/operation.cxx b/build2/config/operation.cxx
index 951da30..a029b60 100644
--- a/build2/config/operation.cxx
+++ b/build2/config/operation.cxx
@@ -479,6 +479,7 @@ namespace build2
 
     static void
     disfigure_search (const scope& root,
+                      const scope&,
                       const target_key&,
                       const location&,
                       action_targets& ts)
diff --git a/build2/operation b/build2/operation
index e6c34d6..39bb799 100644
--- a/build2/operation
+++ b/build2/operation
@@ -206,6 +206,7 @@ namespace build2
                   const location&);
 
     void (*search) (const scope& root,
+                    const scope& base,
                     const target_key&,
                     const location&,
                     action_targets&);
@@ -230,17 +231,21 @@ namespace build2
   // scope.
   //
   void
-  load (scope& root,
-        const path& buildfile,
-        const dir_path& out_base,
-        const dir_path& src_base,
+  load (scope&,
+        const path&,
+        const dir_path&,
+        const dir_path&,
         const location&);
 
   // Search and match the target. This is the default implementation
   // that does just that and adds a pointer to the target to the list.
   //
   void
-  search (const scope&, const target_key&, const location&, action_targets&);
+  search (const scope&,
+          const scope&,
+          const target_key&,
+          const location&,
+          action_targets&);
 
   void
   match (action, action_targets&);
diff --git a/build2/operation.cxx b/build2/operation.cxx
index ff2051d..b821b1d 100644
--- a/build2/operation.cxx
+++ b/build2/operation.cxx
@@ -60,25 +60,32 @@ namespace build2
     auto i (scopes.rw (root).insert (out_base, false));
     scope& base (setup_base (i, out_base, src_base));
 
-    // Load the buildfile unless it has already been loaded.
+    // Load the buildfile unless it is implied.
     //
-    source_once (root, base, bf, root);
+    if (!bf.empty ())
+      source_once (root, base, bf, root);
   }
 
   void
   search (const scope&,
+          const scope& bs,
           const target_key& tk,
           const location& l,
           action_targets& ts)
   {
     tracer trace ("search");
 
-    phase_lock pl (run_phase::match); // Never switched.
+    phase_lock pl (run_phase::match);
 
-    if (const target* t = targets.find (tk, trace))
-      ts.push_back (t);
-    else
+    const target* t (targets.find (tk, trace));
+
+    if (t == nullptr && tk.is_a<dir> ())
+      t = dir::search_implied (bs, tk, trace);
+
+    if (t == nullptr)
       fail (l) << "unknown target " << tk;
+
+    ts.push_back (t);
   }
 
   void
diff --git a/build2/spec b/build2/spec
index 7a7e55e..92b56ec 100644
--- a/build2/spec
+++ b/build2/spec
@@ -28,7 +28,7 @@ namespace build2
     //
     scope* root_scope = nullptr;
     dir_path out_base;
-    path buildfile;
+    path buildfile; // Empty if implied.
   };
 
   struct opspec: vector<targetspec>
diff --git a/build2/target b/build2/target
index ef1e34d..c196060 100644
--- a/build2/target
+++ b/build2/target
@@ -307,7 +307,7 @@ namespace build2
     prerequisites () const;
 
     // Swap-in a list of prerequisites. Return false if unsuccessful (i.e.,
-    // some beat us to it). Note that it can be called on const target.
+    // someone beat us to it). Note that it can be called on const target.
     //
     bool
     prerequisites (prerequisites_type&&) const;
@@ -1473,6 +1473,11 @@ namespace build2
   public:
     static const target_type static_type;
     virtual const target_type& dynamic_type () const {return static_type;}
+
+  public:
+    template <typename K>
+    static const target*
+    search_implied (const scope&, const K&, tracer&);
   };
 
   // While a filesystem directory is mtime-based, the semantics is
diff --git a/build2/target.cxx b/build2/target.cxx
index 676dc6b..668db92 100644
--- a/build2/target.cxx
+++ b/build2/target.cxx
@@ -14,6 +14,7 @@
 #include <build2/diagnostics>
 
 using namespace std;
+using namespace butl;
 
 namespace build2
 {
@@ -732,7 +733,7 @@ namespace build2
     const target* t (search_existing_target (pk));
 
     if (t == nullptr || t->implied)
-      fail << "no explicit target for prerequisite " << pk;
+      fail << "no explicit target for " << pk;
 
     return t;
   }
@@ -762,7 +763,10 @@ namespace build2
       return t;
 
     // If not found (or is implied), then try to load the corresponding
-    // buildfile which would normally define this target.
+    // buildfile (which would normally define this target). Failed that, see
+    // if we can assume an implied buildfile which would be equivalent to:
+    //
+    // ./: */
     //
     const dir_path& d (*pk.tk.dir);
 
@@ -809,18 +813,25 @@ namespace build2
           scope& base (sp.first);
           scope& root (*sp.second);
 
-          path bf (base.src_path () / "buildfile");
+          const dir_path& src_base (base.src_path ());
+
+          path bf (src_base / "buildfile");
 
           if (exists (bf))
           {
             l5 ([&]{trace << "loading buildfile " << bf << " for " << pk;});
             retest = source_once (root, base, bf, root);
           }
+          else if (exists (src_base))
+          {
+            t = dir::search_implied (base, pk, trace);
+            retest = (t != nullptr);
+          }
         }
       }
       assert (phase == run_phase::match);
 
-      // If we loaded the buildfile, examine the target again.
+      // If we loaded/implied the buildfile, examine the target again.
       //
       if (retest)
       {
@@ -832,8 +843,7 @@ namespace build2
       }
     }
 
-    fail << "no explicit target for prerequisite " << pk <<
-      info << "did you forget to include the corresponding buildfile?" << endf;
+    fail << "no explicit target for " << pk << endf;
   }
 
   static bool
diff --git a/build2/target.txx b/build2/target.txx
index dd087c0..d854ed2 100644
--- a/build2/target.txx
+++ b/build2/target.txx
@@ -2,6 +2,8 @@
 // copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
 // license   : MIT; see accompanying LICENSE file
 
+#include <butl/filesystem> // dir_iterator
+
 #include <build2/scope>
 #include <build2/diagnostics>
 #include <build2/prerequisite>
@@ -135,4 +137,48 @@ namespace build2
 
     return false;
   }
+
+  // dir
+  //
+  template <typename K>
+  const target* dir::
+  search_implied (const scope& base, const K& k, tracer& trace)
+  {
+    using namespace butl;
+
+    // See if we have any subdirectories.
+    //
+    prerequisites_type ps;
+
+    for (const dir_entry& e: dir_iterator (base.src_path ()))
+    {
+      if (e.type () == entry_type::directory)
+        ps.push_back (
+          prerequisite (nullopt,
+                        dir::static_type,
+                        dir_path (e.path ().representation ()),
+                        dir_path (), // In the out tree.
+                        string (),
+                        nullopt,
+                        base));
+    }
+
+    if (ps.empty ())
+      return nullptr;
+
+    l5 ([&]{trace << "implying buildfile for " << k;});
+
+    // We behave as if this target was explicitly mentioned in the (implied)
+    // buildfile. Thus not implied.
+    //
+    target& t (targets.insert (dir::static_type,
+                               base.out_path (),
+                               dir_path (),
+                               string (),
+                               nullopt,
+                               false,
+                               trace).first);
+    t.prerequisites (move (ps));
+    return &t;
+  }
 }
diff --git a/tests/function/buildfile b/tests/function/buildfile
deleted file mode 100644
index 8034f2b..0000000
--- a/tests/function/buildfile
+++ /dev/null
@@ -1,5 +0,0 @@
-# file      : tests/function/buildfile
-# copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
-# license   : MIT; see accompanying LICENSE file
-
-./: builtin/ path/
diff --git a/tests/search/buildfile b/tests/search/buildfile
deleted file mode 100644
index a72ca71..0000000
--- a/tests/search/buildfile
+++ /dev/null
@@ -1,5 +0,0 @@
-# file      : tests/search/buildfile
-# copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
-# license   : MIT; see accompanying LICENSE file
-
-./: dir/
diff --git a/tests/search/dir/testscript b/tests/search/dir/testscript
index d580c4f..4cd368b 100644
--- a/tests/search/dir/testscript
+++ b/tests/search/dir/testscript
@@ -20,8 +20,7 @@ EOI
 : no-buildfile
 :
 $* <'./: foo/' 2>>/EOE != 0
-error: no explicit target for prerequisite ../:dir{foo/}
-  info: did you forget to include the corresponding buildfile?
+error: no explicit target for ../:dir{foo/}
 EOE
 
 : basic
diff --git a/tests/variable/buildfile b/tests/variable/buildfile
deleted file mode 100644
index 65a0791..0000000
--- a/tests/variable/buildfile
+++ /dev/null
@@ -1,5 +0,0 @@
-# file      : tests/variable/buildfile
-# copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
-# license   : MIT; see accompanying LICENSE file
-
-./: override/
diff --git a/unit-tests/buildfile b/unit-tests/buildfile
deleted file mode 100644
index 0e39bfe..0000000
--- a/unit-tests/buildfile
+++ /dev/null
@@ -1,5 +0,0 @@
-# file      : unit-tests/buildfile
-# copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
-# license   : MIT; see accompanying LICENSE file
-
-./: function/ lexer/ scheduler/ test/script/
diff --git a/unit-tests/test/script/buildfile b/unit-tests/test/script/buildfile
deleted file mode 100644
index 7e2aa9b..0000000
--- a/unit-tests/test/script/buildfile
+++ /dev/null
@@ -1,5 +0,0 @@
-# file      : unit-tests/test/script/buildfile
-# copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
-# license   : MIT; see accompanying LICENSE file
-
-./: lexer/ parser/ regex/