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-rw-r--r--libbuild2/config/utility.hxx17
1 files changed, 12 insertions, 5 deletions
diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index bafcafa..cb82ea6 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -58,6 +58,10 @@ namespace build2
{
// Mark a variable to be saved during configuration.
//
+ // Note: the save_*_omitted flags work best when undefined or (one of) the
+ // omitted value(s) is the default (see a note in lookup_config()
+ // documentation for details).
+ //
const uint64_t save_default_commented = 0x01; // Based on value::extra.
const uint64_t save_null_omitted = 0x02; // Treat NULL as undefined.
const uint64_t save_empty_omitted = 0x04; // Treat empty as undefined.
@@ -242,9 +246,6 @@ namespace build2
// expensive. It is also ok to call both versions multiple times provided
// the flags are the same.
//
- // @@ Should save_null_omitted be interpreted to treat null as undefined?
- // Sounds logical.
- //
lookup
lookup_config (scope& rs,
const variable&,
@@ -300,8 +301,14 @@ namespace build2
// or from the command line (i.e., it is inherited from the amalgamation),
// then its value is "overridden" to the default value on this root scope.
//
- // @@ Should save_null_omitted be interpreted to treat null as undefined?
- // Sounds logical.
+ // Note that while it may seem logical, these functions do not
+ // "reinterpret" defined values according to the save_*_omitted flags (for
+ // example, by returning the default value if the defined value is NULL
+ // and the save_null_omitted flag is specified). This is because such a
+ // reinterpretation may cause a diversion between the returned value and
+ // the re-queried config.* variable value if the defined value came from
+ // an override. To put another way, the save_*_omitted flags are purely to
+ // reduce the noise in config.build.
//
template <typename T>
lookup