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-rw-r--r--libbuild2/context.hxx28
1 files changed, 25 insertions, 3 deletions
diff --git a/libbuild2/context.hxx b/libbuild2/context.hxx
index 2a9c93e..5f6e810 100644
--- a/libbuild2/context.hxx
+++ b/libbuild2/context.hxx
@@ -348,14 +348,36 @@ namespace build2
//
const variable* var_project_summary;
- // import.*
+ // import.* and export.*
//
const variable* var_import_build2;
const variable* var_import_target;
- const variable* var_import_metadata;
- // export.*
+ // The import.metadata variable and the --build2-metadata option are used
+ // to pass the metadata compatibility version.
+ //
+ // This serves both as an indication that the metadata is required (can be
+ // useful, for example, in cases where it is expensive to calculate) as
+ // well as the maximum version we recognize. The exporter may return it in
+ // any version up to and including this maximum. And it may return it even
+ // if not requested (but only in version 1). The exporter should also set
+ // the returned version as the target-specific export.metadata variable.
+ //
+ // The export.metadata value should start with the version optionally
+ // followed by the metadata variable prefix (for example, cli in
+ // cli.version). If the variable prefix is missing, it is assumed to be
+ // the target name as imported.
+ //
+ // The following metadata variable names have pre-defined meaning:
//
+ // <var-prefix>.name = [string] # Stable name for diagnostics.
+ // <var-prefix>.version = [string] # Version for diagnostics.
+ // <var-prefix>.checksum = [string] # Checksum for change tracking.
+ //
+ // If the <var-prefix>.name variable is missing, it is set to the target
+ // name as imported.
+ //
+ const variable* var_import_metadata;
const variable* var_export_metadata;
// [string] target visibility