Add build.version.interface

This build system interface version should be embedded into build system
modules as load_suffix.

4 files changed, 23 insertions, 6 deletions

diff --git a/libbuild2/bash/buildfile b/libbuild2/bash/buildfile
index ed95998..e30f379 100644
--- a/libbuild2/bash/buildfile
+++ b/libbuild2/bash/buildfile
@@ -50,8 +50,10 @@ libs{build2-bash}: cxx.export.poptions += -DLIBBUILD2_BASH_SHARED
 # in place of another pre-release or the final version. See the version module
 # for details on the version.* variable values.
 #
-# And seeing that this is a build system module, we also embed the same
-# version as the build system core version.
+# And because this is a build system module, we also embed the same value as
+# the interface version (note that we cannot use build.version.interface for
+# bundled modules because we could be built with a different version of the
+# build system).
 #
 ver = ($version.pre_release    \
        ? "$version.project_id" \
diff --git a/libbuild2/context.cxx b/libbuild2/context.cxx
index 815a556..e7f9751 100644
--- a/libbuild2/context.cxx
+++ b/libbuild2/context.cxx
@@ -432,6 +432,9 @@ namespace build2
         gs.assign (variable_pool::instance.insert<T> (var)) = move (val);
       };
 
+      // Note: here we assume epoch will always be 1 and therefore omit the
+      //       project_ prefix in a few places.
+      //
       set ("build.version", v.string_project ());
 
       set ("build.version.number", v.version);
@@ -455,6 +458,14 @@ namespace build2
       set ("build.version.snapshot_id",     v.snapshot_id); // string
       set ("build.version.snapshot_string", v.string_snapshot ());
 
+      // Build system interface version. In particular, it is embedded into
+      // build system modules as load_suffix.
+      //
+      set ("build.version.interface",
+           v.pre_release ()
+           ? v.string_project_id ()
+           : to_string (v.major ()) + '.' + to_string (v.minor ()));
+
       // Allow detection (for example, in tests) whether this is a staged
       // toolchain.
       //
diff --git a/libbuild2/in/buildfile b/libbuild2/in/buildfile
index aa5af87..b67ee00 100644
--- a/libbuild2/in/buildfile
+++ b/libbuild2/in/buildfile
@@ -47,8 +47,10 @@ libs{build2-in}: cxx.export.poptions += -DLIBBUILD2_IN_SHARED
 # in place of another pre-release or the final version. See the version module
 # for details on the version.* variable values.
 #
-# And seeing that this is a build system module, we also embed the same
-# version as the build system core version.
+# And because this is a build system module, we also embed the same value as
+# the interface version (note that we cannot use build.version.interface for
+# bundled modules because we could be built with a different version of the
+# build system).
 #
 ver = ($version.pre_release    \
        ? "$version.project_id" \
diff --git a/libbuild2/version/buildfile b/libbuild2/version/buildfile
index 7477815..96f55ad 100644
--- a/libbuild2/version/buildfile
+++ b/libbuild2/version/buildfile
@@ -51,8 +51,10 @@ libs{build2-version}: cxx.export.poptions += -DLIBBUILD2_VERSION_SHARED
 # in place of another pre-release or the final version. See the version module
 # for details on the version.* variable values.
 #
-# And seeing that this is a build system module, we also embed the same
-# version as the build system core version.
+# And because this is a build system module, we also embed the same value as
+# the interface version (note that we cannot use build.version.interface for
+# bundled modules because we could be built with a different version of the
+# build system).
 #
 ver = ($version.pre_release    \
        ? "$version.project_id" \