Add ability to extend rule interface in source-compatible manner

12 files changed, 68 insertions, 23 deletions

diff --git a/build2/cli/rule.hxx b/build2/cli/rule.hxx
index 64f1614..b3ecc2c 100644
--- a/build2/cli/rule.hxx
+++ b/build2/cli/rule.hxx
@@ -23,7 +23,7 @@ namespace build2
 
     // @@ Redo as two separate rules?
     //
-    class compile_rule: public rule, virtual data
+    class compile_rule: public simple_rule, virtual data
     {
     public:
       compile_rule (data&& d): data (move (d)) {}
diff --git a/libbuild2/adhoc-rule-cxx.hxx b/libbuild2/adhoc-rule-cxx.hxx
index 9b94783..fbcdd4f 100644
--- a/libbuild2/adhoc-rule-cxx.hxx
+++ b/libbuild2/adhoc-rule-cxx.hxx
@@ -18,7 +18,7 @@ namespace build2
   //
   // Note: exported but should not be used directly (i.e., registered).
   //
-  class LIBBUILD2_SYMEXPORT cxx_rule: public rule
+  class LIBBUILD2_SYMEXPORT cxx_rule: public simple_rule
   {
     // For now this class is provided purely as an alias for rule in case the
     // implementation (which is also called rule) needs to refer to something
diff --git a/libbuild2/algorithm.cxx b/libbuild2/algorithm.cxx
index de68be2..e1f30e0 100644
--- a/libbuild2/algorithm.cxx
+++ b/libbuild2/algorithm.cxx
@@ -450,7 +450,8 @@ namespace build2
                        << diag_do (a, t);
                 });
 
-              if (!ru.match (a, t, hint))
+              rule::match_extra me;
+              if (!ru.match (a, t, hint, me))
                 continue;
             }
 
@@ -479,7 +480,8 @@ namespace build2
                 //
                 // @@ Can't we temporarily swap things out in target?
                 //
-                if (!ru1.match (a, t, hint))
+                rule::match_extra me1;
+                if (!ru1.match (a, t, hint, me1))
                   continue;
               }
 
@@ -527,7 +529,8 @@ namespace build2
              << diag_do (a, t);
       });
 
-    return r.second.get ().apply (a, t);
+    rule::match_extra me;
+    return r.second.get ().apply (a, t, me);
   }
 
   // If step is true then perform only one step of the match/apply sequence.
diff --git a/libbuild2/bin/rule.hxx b/libbuild2/bin/rule.hxx
index 074b46d..51693a7 100644
--- a/libbuild2/bin/rule.hxx
+++ b/libbuild2/bin/rule.hxx
@@ -18,7 +18,7 @@ namespace build2
     // "Fail rule" for obj{}, [h]bmi{}, and libu{} that issues diagnostics if
     // someone tries to build any of these groups directly.
     //
-    class fail_rule: public rule
+    class fail_rule: public simple_rule
     {
     public:
       fail_rule () {}
@@ -32,7 +32,7 @@ namespace build2
 
     // Pass-through to group members rule, similar to alias.
     //
-    class LIBBUILD2_BIN_SYMEXPORT lib_rule: public rule
+    class LIBBUILD2_BIN_SYMEXPORT lib_rule: public simple_rule
     {
     public:
       lib_rule () {}
diff --git a/libbuild2/cc/compile-rule.hxx b/libbuild2/cc/compile-rule.hxx
index 051b2e3..d6cb002 100644
--- a/libbuild2/cc/compile-rule.hxx
+++ b/libbuild2/cc/compile-rule.hxx
@@ -36,7 +36,7 @@ namespace build2
       size_t copied;   // First copied-over bmi*{}, 0 if none.
     };
 
-    class LIBBUILD2_CC_SYMEXPORT compile_rule: public rule, virtual common
+    class LIBBUILD2_CC_SYMEXPORT compile_rule: public simple_rule, virtual common
     {
     public:
       compile_rule (data&&);
diff --git a/libbuild2/cc/link-rule.hxx b/libbuild2/cc/link-rule.hxx
index ce514b5..7a357a6 100644
--- a/libbuild2/cc/link-rule.hxx
+++ b/libbuild2/cc/link-rule.hxx
@@ -20,7 +20,7 @@ namespace build2
 {
   namespace cc
   {
-    class LIBBUILD2_CC_SYMEXPORT link_rule: public rule, virtual common
+    class LIBBUILD2_CC_SYMEXPORT link_rule: public simple_rule, virtual common
     {
     public:
       link_rule (data&&);
diff --git a/libbuild2/dist/rule.hxx b/libbuild2/dist/rule.hxx
index 28caa68..e63016d 100644
--- a/libbuild2/dist/rule.hxx
+++ b/libbuild2/dist/rule.hxx
@@ -23,7 +23,7 @@ namespace build2
     // bin::lib_rule for an example). Note that in the latter case the rule
     // should "see" all its members for the dist case.
     //
-    class rule: public build2::rule
+    class rule: public simple_rule
     {
     public:
       rule () {}
diff --git a/libbuild2/in/rule.hxx b/libbuild2/in/rule.hxx
index 653818f..cf67060 100644
--- a/libbuild2/in/rule.hxx
+++ b/libbuild2/in/rule.hxx
@@ -23,7 +23,7 @@ namespace build2
     // Note also that currently this rule ignores the dry-run mode (see
     // perform_update() for the rationale).
     //
-    class LIBBUILD2_IN_SYMEXPORT rule: public build2::rule
+    class LIBBUILD2_IN_SYMEXPORT rule: public simple_rule
     {
     public:
       // The rule id is used to form the rule name/version entry in depdb. The
diff --git a/libbuild2/install/rule.hxx b/libbuild2/install/rule.hxx
index 916fc6d..73f2486 100644
--- a/libbuild2/install/rule.hxx
+++ b/libbuild2/install/rule.hxx
@@ -18,7 +18,7 @@ namespace build2
 {
   namespace install
   {
-    class LIBBUILD2_SYMEXPORT alias_rule: public rule
+    class LIBBUILD2_SYMEXPORT alias_rule: public simple_rule
     {
     public:
       virtual bool
@@ -46,7 +46,7 @@ namespace build2
       static const alias_rule instance;
     };
 
-    class fsdir_rule: public rule
+    class fsdir_rule: public simple_rule
     {
     public:
       virtual bool
@@ -95,7 +95,7 @@ namespace build2
 
     struct install_dir;
 
-    class LIBBUILD2_SYMEXPORT file_rule: public rule
+    class LIBBUILD2_SYMEXPORT file_rule: public simple_rule
     {
     public:
       virtual bool
diff --git a/libbuild2/rule.cxx b/libbuild2/rule.cxx
index 9028096..7ccee4e 100644
--- a/libbuild2/rule.cxx
+++ b/libbuild2/rule.cxx
@@ -22,6 +22,20 @@ namespace build2
   {
   }
 
+  // simple_rule
+  //
+  bool simple_rule::
+  match (action a, target& t, const string& h, match_extra&) const
+  {
+    return match (a, t, h);
+  }
+
+  recipe simple_rule::
+  apply (action a, target& t, match_extra&) const
+  {
+    return apply (a, t);
+  }
+
   // file_rule
   //
   // Note that this rule is special. It is the last, fallback rule. If
diff --git a/libbuild2/rule.hxx b/libbuild2/rule.hxx
index 8390ea7..298ed6b 100644
--- a/libbuild2/rule.hxx
+++ b/libbuild2/rule.hxx
@@ -16,20 +16,30 @@
 
 namespace build2
 {
+  // Rule interface (see also simple_rule below for a simplified version).
+  //
   // Once a rule is registered (for a scope), it is treated as immutable. If
   // you need to modify some state (e.g., counters or some such), then make
-  // sure it is MT-safe.
+  // sure things are MT-safe.
   //
   // Note: match() is only called once but may not be followed by apply().
   //
   class LIBBUILD2_SYMEXPORT rule
   {
   public:
+    // The match_extra argument is used to pass additional information that is
+    // only needed by some rule implementations. It is also a way for us to
+    // later pass more information without breaking source compatibility.
+    //
+    struct match_extra
+    {
+    };
+
     virtual bool
-    match (action, target&, const string& hint) const = 0;
+    match (action, target&, const string& hint, match_extra&) const = 0;
 
     virtual recipe
-    apply (action, target&) const = 0;
+    apply (action, target&, match_extra&) const = 0;
 
     rule () = default;
 
@@ -40,10 +50,28 @@ namespace build2
     rule& operator= (const rule&) = delete;
   };
 
+  // Simplified interface for rules that don't care about the extras.
+  //
+  class LIBBUILD2_SYMEXPORT simple_rule: public rule
+  {
+  public:
+    virtual bool
+    match (action, target&, const string& hint) const = 0;
+
+    virtual recipe
+    apply (action, target&) const = 0;
+
+    virtual bool
+    match (action, target&, const string&, match_extra&) const override;
+
+    virtual recipe
+    apply (action, target&, match_extra&) const override;
+  };
+
   // Fallback rule that only matches if the file exists. It will also match
   // an mtime_target provided it has a set timestamp.
   //
-  class LIBBUILD2_SYMEXPORT file_rule: public rule
+  class LIBBUILD2_SYMEXPORT file_rule: public simple_rule
   {
   public:
     virtual bool
@@ -56,7 +84,7 @@ namespace build2
     static const file_rule instance;
   };
 
-  class LIBBUILD2_SYMEXPORT alias_rule: public rule
+  class LIBBUILD2_SYMEXPORT alias_rule: public simple_rule
   {
   public:
     virtual bool
@@ -72,7 +100,7 @@ namespace build2
   // Note that this rule ignores the dry_run flag; see mkdir() in filesystem
   // for the rationale.
   //
-  class LIBBUILD2_SYMEXPORT fsdir_rule: public rule
+  class LIBBUILD2_SYMEXPORT fsdir_rule: public simple_rule
   {
   public:
     virtual bool
@@ -99,7 +127,7 @@ namespace build2
 
   // Fallback rule that always matches and does nothing.
   //
-  class LIBBUILD2_SYMEXPORT noop_rule: public rule
+  class LIBBUILD2_SYMEXPORT noop_rule: public simple_rule
   {
   public:
     virtual bool
@@ -116,7 +144,7 @@ namespace build2
   //
   // Note: not exported.
   //
-  class adhoc_rule: public rule
+  class adhoc_rule: public simple_rule
   {
   public:
     location_value loc;     // Buildfile location of the recipe.
diff --git a/libbuild2/test/rule.hxx b/libbuild2/test/rule.hxx
index bc39f50..e96b68b 100644
--- a/libbuild2/test/rule.hxx
+++ b/libbuild2/test/rule.hxx
@@ -16,7 +16,7 @@ namespace build2
 {
   namespace test
   {
-    class rule: public build2::rule, protected virtual common
+    class rule: public simple_rule, protected virtual common
     {
     public:
       virtual bool