Add support for config.build file versioning

9 files changed, 116 insertions, 38 deletions

diff --git a/build2/b.cxx b/build2/b.cxx
index bb4f0fe..6d6723a 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -297,6 +297,7 @@ main (int argc, char* argv[])
     {
       vector_view<opspec> opspecs;
       const string& mname (lifted == nullptr ? mit->name : lifted->name);
+      current_mname = &mname;
 
       if (lifted == nullptr)
       {
@@ -345,6 +346,7 @@ main (int argc, char* argv[])
         // A lifted meta-operation will always have default operation.
         //
         const string& oname (lifted == nullptr ? os.name : string ());
+        current_oname = &oname;
 
         if (lifted != nullptr)
           lifted = nullptr; // Clear for the next iteration.
@@ -719,7 +721,7 @@ main (int argc, char* argv[])
               if (mif->meta_operation_pre != nullptr)
                 mif->meta_operation_pre ();
 
-              current_mif = mif;
+              set_current_mif (*mif);
               dirty = true;
             }
             //
@@ -973,9 +975,7 @@ main (int argc, char* argv[])
           if (mif->operation_pre != nullptr)
             mif->operation_pre (pre_oid); // Cannot be translated.
 
-          current_inner_oif = pre_oif;
-          current_outer_oif = oif;
-          current_mode = pre_oif->mode;
+          set_current_oif (*pre_oif, oif);
           dependency_count = 0;
 
           action a (mid, pre_oid, oid);
@@ -990,9 +990,7 @@ main (int argc, char* argv[])
                         << ", id " << static_cast<uint16_t> (pre_oid);});
         }
 
-        current_inner_oif = oif;
-        current_outer_oif = nullptr;
-        current_mode = oif->mode;
+        set_current_oif (*oif);
         dependency_count = 0;
 
         action a (mid, oid, 0);
@@ -1008,9 +1006,7 @@ main (int argc, char* argv[])
           if (mif->operation_pre != nullptr)
             mif->operation_pre (post_oid); // Cannot be translated.
 
-          current_inner_oif = post_oif;
-          current_outer_oif = oif;
-          current_mode = post_oif->mode;
+          set_current_oif (*post_oif, oif);
           dependency_count = 0;
 
           action a (mid, post_oid, oid);
diff --git a/build2/config/init.cxx b/build2/config/init.cxx
index 6c713df..368b9d0 100644
--- a/build2/config/init.cxx
+++ b/build2/config/init.cxx
@@ -23,9 +23,10 @@ namespace build2
   namespace config
   {
     const string module::name ("config");
+    const uint64_t module::version;
 
     void
-    boot (scope& rs, const location&, unique_ptr<module_base>&)
+    boot (scope& rs, const location& loc, unique_ptr<module_base>&)
     {
       tracer trace ("config::boot");
 
@@ -44,10 +45,44 @@ namespace build2
       // possible that some module which needs the configuration will get
       // called first.
       //
-      path f (out_root / config_file);
+      const variable& c_v (var_pool.insert<uint64_t> ("config.version"));
 
-      if (file_exists (f))
-        source (f, rs, rs);
+      // Don't load it if we are disfiguring. This is a bit tricky since the
+      // build2 core may not yet know it is disfiguring. But we know.
+      //
+      if (*current_mname != disfigure.name &&
+          (!current_mname->empty () || *current_oname != disfigure.name))
+      {
+        path f (out_root / config_file);
+
+        if (file_exists (f))
+        {
+          // Check the config version. We assume that old versions cannot
+          // understand new configs and new versions are incompatible with old
+          // configs.
+          //
+          // We extract the value manually instead of loading and then
+          // checking in order to be able to fixup/migrate the file which we
+          // may want to do in the future.
+          //
+          {
+            // Assume missing version is 0.
+            //
+            auto p (extract_variable (f, c_v.name.c_str ()));
+            uint64_t v (p.second ? cast<uint64_t> (p.first) : 0);
+
+            if (v != module::version)
+              fail (loc) << "incompatible config file " << f <<
+                info << "config file version   " << v
+                         << (p.second ? "" : " (missing)") <<
+                info << "config module version " << module::version <<
+                info << "consider reconfiguring " << project (rs) << '@'
+                         << out_root;
+          }
+
+          source (f, rs, rs);
+        }
+      }
     }
 
     bool
diff --git a/build2/config/module b/build2/config/module
index e6fb197..8f9a9b9 100644
--- a/build2/config/module
+++ b/build2/config/module
@@ -78,7 +78,9 @@ namespace build2
     struct module: module_base
     {
       config::saved_modules saved_modules;
+
       static const string name; // init.cxx
+      static constexpr const uint64_t version = 1;
     };
   }
 }
diff --git a/build2/config/operation.cxx b/build2/config/operation.cxx
index 90c2bbb..e6ab14a 100644
--- a/build2/config/operation.cxx
+++ b/build2/config/operation.cxx
@@ -80,6 +80,8 @@ namespace build2
           "free to edit." << endl
             << "#" << endl;
 
+        ofs << "config.version = " << module::version << endl;
+
         if (auto l = root.vars["amalgamation"])
         {
           const dir_path& d (cast<dir_path> (l));
@@ -371,13 +373,11 @@ namespace build2
              id < rs->operations.size ();
              ++id)
         {
-          const operation_info* oi (rs->operations[id]);
-          if (oi == nullptr)
+          const operation_info* oif (rs->operations[id]);
+          if (oif == nullptr)
             continue;
 
-          current_inner_oif = oi;
-          current_outer_oif = nullptr;
-          current_mode = oi->mode;
+          set_current_oif (*oif);
           dependency_count = 0;
 
           match (action (configure_id, id), t);
diff --git a/build2/context b/build2/context
index e7b8c7d..257e96b 100644
--- a/build2/context
+++ b/build2/context
@@ -26,12 +26,35 @@ namespace build2
 
   // Current action (meta/operation).
   //
+  // The names unlike info are available during boot but may not yet be
+  // lifted. The name is always for an outer operation (or meta operation
+  // that hasn't been recognized as such yet).
+  //
+  extern const string* current_mname;
+  extern const string* current_oname;
+
   extern const meta_operation_info* current_mif;
   extern const operation_info* current_inner_oif;
   extern const operation_info* current_outer_oif;
-
   extern execution_mode current_mode;
 
+  inline void
+  set_current_mif (const meta_operation_info& mif)
+  {
+    current_mif = &mif;
+    current_mname = &mif.name;
+  }
+
+  inline void
+  set_current_oif (const operation_info& inner_oif,
+                   const operation_info* outer_oif = nullptr)
+  {
+    current_inner_oif = &inner_oif;
+    current_outer_oif = outer_oif;
+    current_oname = &(outer_oif == nullptr ? inner_oif : *outer_oif).name;
+    current_mode = inner_oif.mode;
+  }
+
   // Total number of dependency relationships in the current action.
   // Together with the target::dependents count it is incremented
   // during the rule search & match phase and is decremented during
diff --git a/build2/context.cxx b/build2/context.cxx
index ac972ac..0e05926 100644
--- a/build2/context.cxx
+++ b/build2/context.cxx
@@ -32,10 +32,15 @@ namespace build2
   string_pool extension_pool;
   string_pool project_name_pool;
 
+  const string* current_mname;
+  const string* current_oname;
+
   const meta_operation_info* current_mif;
   const operation_info* current_inner_oif;
   const operation_info* current_outer_oif;
+
   execution_mode current_mode;
+
   uint64_t dependency_count;
 
   variable_overrides
diff --git a/build2/dist/operation.cxx b/build2/dist/operation.cxx
index d03fe28..12bcc61 100644
--- a/build2/dist/operation.cxx
+++ b/build2/dist/operation.cxx
@@ -101,17 +101,15 @@ namespace build2
            id < rs->operations.size ();
            ++id)
       {
-        const operation_info* oi (rs->operations[id]);
-        if (oi == nullptr)
+        const operation_info* oif (rs->operations[id]);
+        if (oif == nullptr)
           continue;
 
         // Note that we are not calling operation_pre/post() callbacks
         // here since the meta operation is dist and we know what we
         // are doing.
         //
-        current_inner_oif = oi;
-        current_outer_oif = nullptr;
-        current_mode = oi->mode;
+        set_current_oif (*oif);
         dependency_count = 0;
 
         action a (dist_id, id);
@@ -237,14 +235,12 @@ namespace build2
         if (perform.meta_operation_pre != nullptr)
           perform.meta_operation_pre ();
 
-        current_mif = &perform;
+        set_current_mif (perform);
 
         if (perform.operation_pre != nullptr)
           perform.operation_pre (update_id);
 
-        current_inner_oif = &update;
-        current_outer_oif = nullptr;
-        current_mode = update.mode;
+        set_current_oif (update);
         dependency_count = 0;
 
         action a (perform_id, update_id);
diff --git a/build2/file b/build2/file
index f5dac83..1502d73 100644
--- a/build2/file
+++ b/build2/file
@@ -129,6 +129,14 @@ namespace build2
   void
   load_root_pre (scope& root);
 
+  // Extract the specified variable value from a buildfile. It is expected to
+  // be the first non-comment line and not to rely on any variable expansion
+  // other than those from the global scope or any variable overrides. Return
+  // an indication of whether the variable was found.
+  //
+  pair<value, bool>
+  extract_variable (const path&, const char* var);
+
   // Import has two phases: the first is triggered by the import
   // directive in the buildfile. It will try to find and load the
   // project. Failed that, it will return the project-qualified
diff --git a/build2/file.cxx b/build2/file.cxx
index d267fec..46362e1 100644
--- a/build2/file.cxx
+++ b/build2/file.cxx
@@ -272,7 +272,7 @@ namespace build2
   // be the first non-comment line and not to rely on any variable expansion
   // other than those from the global scope or any variable overrides.
   //
-  static value
+  pair<value, bool>
   extract_variable (const path& bf, const char* name)
   {
     try
@@ -288,8 +288,7 @@ namespace build2
            tt != token_type::prepend &&
            tt != token_type::append))
       {
-        error << "variable '" << name << "' expected as first line in " << bf;
-        throw failed (); // Suppress "used uninitialized" warning.
+        return make_pair (value (), false);
       }
 
       const variable& var (var_pool.find (move (t.value)));
@@ -300,14 +299,18 @@ namespace build2
 
       value* v (tmp.vars.find (var));
       assert (v != nullptr);
-      return move (*v); // Steal the value, the scope is going away.
+
+      // Steal the value, the scope is going away.
+      //
+      return make_pair (move (*v), true);
     }
     catch (const ifdstream::failure& e)
     {
-      fail << "unable to read buildfile " << bf << ": " << e.what ();
+      error << "unable to read buildfile " << bf << ": " << e.what ();
+      throw failed ();
     }
 
-    return value (); // Never reaches.
+    // Never reached.
   }
 
   // Extract the project name from bootstrap.build.
@@ -336,7 +339,12 @@ namespace build2
         src_root = &fallback_src_root;
       else
       {
-        src_root_v = extract_variable (f, "src_root");
+        auto p (extract_variable (f, "src_root"));
+
+        if (!p.second)
+          error << "variable 'src_root' expected as first line in " << f;
+
+        src_root_v = move (p.first);
         src_root = &cast<dir_path> (src_root_v);
         l5 ([&]{trace << "extracted src_root " << *src_root << " for "
                       << out_root;});
@@ -345,8 +353,13 @@ namespace build2
 
     string name;
     {
-      value v (extract_variable (*src_root / bootstrap_file, "project"));
-      name = cast<string> (move (v));
+      path f (*src_root / bootstrap_file);
+      auto p (extract_variable (f, "project"));
+
+      if (!p.second)
+        error << "variable 'project' expected as first line in " << f;
+
+      name = cast<string> (move (p.first));
     }
 
     l5 ([&]{trace << "extracted project name '" << name << "' for "