From 5058b155076b004f4abf21be6cf657a3f2cc4d1b Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Sun, 20 Aug 2017 15:56:26 +0200
Subject: Add support for not cleaning generated version file

---
 build2/context.cxx      |  4 ++++
 build2/context.hxx      |  4 +++-
 build2/variable.hxx     | 14 +++++++++-----
 build2/variable.ixx     |  9 +++++++++
 build2/version/rule.cxx |  5 +++++
 5 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/build2/context.cxx b/build2/context.cxx
index 11c2c63..f7f2448 100644
--- a/build2/context.cxx
+++ b/build2/context.cxx
@@ -191,6 +191,8 @@ namespace build2
 
   const variable* var_import_target;
 
+  const variable* var_clean;
+
   const string* current_mname;
   const string* current_oname;
 
@@ -538,6 +540,8 @@ namespace build2
       var_project_summary = &vp.insert<string> ("project.summary", pv);
 
       var_import_target = &vp.insert<name> ("import.target");
+
+      var_clean = &vp.insert<bool> ("clean", variable_visibility::target);
     }
 
     // Register builtin rules.
diff --git a/build2/context.hxx b/build2/context.hxx
index bf31887..dbb41ae 100644
--- a/build2/context.hxx
+++ b/build2/context.hxx
@@ -254,7 +254,9 @@ namespace build2
   extern const variable* var_project_url;     // project.url
   extern const variable* var_project_summary; // project.summary
 
-  extern const variable* var_import_target; // import.target
+  extern const variable* var_import_target;   // import.target
+
+  extern const variable* var_clean;           // [bool] target visibility
 
   // Current action (meta/operation).
   //
diff --git a/build2/variable.hxx b/build2/variable.hxx
index decc300..5ef67fd 100644
--- a/build2/variable.hxx
+++ b/build2/variable.hxx
@@ -283,12 +283,16 @@ namespace build2
   template <typename T> const T* cast_null (const value&);
   template <typename T> const T* cast_null (const lookup&);
 
-  // As above but returns false if the value is NULL (or not defined, in case
-  // of lookup). Note that the template argument is only for documentation and
-  // should be bool (or semantically compatible).
+  // As above but returns false/true if the value is NULL (or not defined,
+  // in case of lookup). Note that the template argument is only for
+  // documentation and should be bool (or semantically compatible).
   //
-  template <typename T> T cast_false (const value& v);
-  template <typename T> T cast_false (const lookup& l);
+  template <typename T> T cast_false (const value&);
+  template <typename T> T cast_false (const lookup&);
+
+  template <typename T> T cast_true (const value&);
+  template <typename T> T cast_true (const lookup&);
+
 
   // Assign value type to the value. In the second version the variable is
   // optional and is only used for diagnostics.
diff --git a/build2/variable.ixx b/build2/variable.ixx
index 8656a04..04cf6dc 100644
--- a/build2/variable.ixx
+++ b/build2/variable.ixx
@@ -193,6 +193,15 @@ namespace build2
   cast_false (const lookup& l) {return l && cast<T> (l);}
 
   template <typename T>
+  inline T
+  cast_true (const value& v) {return !v || cast<T> (v);}
+
+  template <typename T>
+  inline T
+  cast_true (const lookup& l) {return !l || cast<T> (l);}
+
+
+  template <typename T>
   inline void
   typify (value& v, const variable& var)
   {
diff --git a/build2/version/rule.cxx b/build2/version/rule.cxx
index a9d62ba..3c9723e 100644
--- a/build2/version/rule.cxx
+++ b/build2/version/rule.cxx
@@ -81,6 +81,11 @@ namespace build2
     {
       doc& t (static_cast<doc&> (xt));
 
+      // If this is clean check if we were asked not to remove it.
+      //
+      if (a == perform_clean_id && !cast_true<bool> (t[var_clean]))
+        return noop_recipe;
+
       // Derive the file name.
       //
       t.derive_path ();
-- 
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