Assign pre-defined semantics to config.<project>.develop variables

This variable allows a project to distinguish between development and
consumption builds. While normally there is no distinction between these two
modes, sometimes a project may need to provide additional functionality during
development. For example, a source code generator which uses its own generated
code in its implementation may need to provide a bootstrap step from the
pre-generated code. Normally, such a step is only needed during development.
See "Project Configuration" in the manual for details.

4 files changed, 59 insertions, 24 deletions

diff --git a/libbuild2/config/operation.cxx b/libbuild2/config/operation.cxx
index c62528f..5883d8c 100644
--- a/libbuild2/config/operation.cxx
+++ b/libbuild2/config/operation.cxx
@@ -221,17 +221,32 @@ namespace build2
           if (size_t n = var->override ())
             var = vp.find (string (var->name, 0, n));
 
+          const string& name (var->name);
+
           // Skip special variables.
           //
-          if (var->name == "config.booted"                   ||
-              var->name == "config.loaded"                   ||
-              var->name == "config.configured"               ||
-              var->name.compare (0, 14, "config.config.") == 0)
+          if (name == "config.booted"                   ||
+              name == "config.loaded"                   ||
+              name == "config.configured"               ||
+              name.compare (0, 14, "config.config.") == 0)
             continue;
 
           if (mod.find_variable (*var)) // Saved or unsaved.
             continue;
 
+          // Skip config.**.develop variables (see parser::parse_config() for
+          // details).
+          //
+          // In a sense, this variable is always "available" but if the
+          // package does not distinguish between development and consumption,
+          // then specifying config.*.develop=true should be noop.
+          //
+          {
+            size_t p (name.rfind ('.'));
+            if (p != 6 && name.compare (p + 1, string::npos, "develop") == 0)
+              continue;
+          }
+
           const value& v (p.first->second);
 
           pair<bool, bool> r (save_config_variable (*var,
@@ -312,9 +327,13 @@ namespace build2
             // inherited. We might also not have any value at all (see
             // unconfigured()).
             //
+            // Note that we must check for null() before attempting any
+            // further tests.
+            //
             if (!l.defined () ||
                 (l->null     ? flags & save_null_omitted  :
-                 l->empty () ? flags & save_empty_omitted : false))
+                 l->empty () ? flags & save_empty_omitted :
+                 (flags & save_false_omitted) != 0 && !cast<bool> (*l)))
               continue;
 
             // Handle inherited from outer scope values.
diff --git a/libbuild2/config/utility.cxx b/libbuild2/config/utility.cxx
index 1f1ac08..928709a 100644
--- a/libbuild2/config/utility.cxx
+++ b/libbuild2/config/utility.cxx
@@ -21,7 +21,7 @@ namespace build2
   namespace config
   {
     pair<lookup, bool>
-    lookup_config_impl (scope& rs, const variable& var)
+    lookup_config_impl (scope& rs, const variable& var, uint64_t sflags)
     {
       // This is a stripped-down version of the default value case.
 
@@ -71,7 +71,7 @@ namespace build2
       }
 
       if (l.defined ())
-        save_variable (rs, var);
+        save_variable (rs, var, sflags);
 
       return pair<lookup, bool> (l, n);
     }
diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index cec4bc3..bafcafa 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -61,7 +61,8 @@ namespace build2
     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.
-    const uint64_t save_base              = 0x08; // Custom save with base.
+    const uint64_t save_false_omitted     = 0x08; // Treat false as undefined.
+    const uint64_t save_base              = 0x10; // Custom save with base.
 
     inline void
     save_variable (scope& rs, const variable& var, uint64_t flags = 0)
@@ -228,9 +229,11 @@ namespace build2
     //
     // Unlike the rest of the lookup_config() versions, this one leaves the
     // unspecified value as undefined rather than setting it to a default
-    // value. This can be useful when we don't have a default value or in case
-    // we want the mentioning of the variable to be omitted from persistent
-    // storage (e.g., a config file) if the default value is used.
+    // value (in this case it also doesn't mark the variable for saving with
+    // the specified flags). This can be useful when we don't have a default
+    // value or in case we want the mentioning of the variable to be omitted
+    // from persistent storage (e.g., a config file) if the default value is
+    // used.
     //
     // Note also that we can first do the lookup without the default value and
     // then, if there is no value, call the version with the default value and
@@ -239,27 +242,37 @@ namespace build2
     // expensive. It is also ok to call both versions multiple times provided
     // the flags are the same.
     //
-    // @@ Should we pass flags and interpret save_null_omitted to treat null
-    //    as undefined? Sounds logical.
+    // @@ Should save_null_omitted be interpreted to treat null as undefined?
+    //    Sounds logical.
     //
     lookup
-    lookup_config (scope& rs, const variable&);
+    lookup_config (scope& rs,
+                   const variable&,
+                   uint64_t save_flags = 0);
 
     lookup
-    lookup_config (bool& new_value, scope& rs, const variable&);
+    lookup_config (bool& new_value,
+                   scope& rs,
+                   const variable&,
+                   uint64_t save_flags = 0);
 
     // Note that the variable is expected to have already been entered.
     //
     inline lookup
-    lookup_config (scope& rs, const string& var)
+    lookup_config (scope& rs,
+                   const string& var,
+                   uint64_t save_flags = 0)
     {
-      return lookup_config (rs, rs.ctx.var_pool[var]);
+      return lookup_config (rs, rs.ctx.var_pool[var], save_flags);
     }
 
     inline lookup
-    lookup_config (bool& new_value, scope& rs, const string& var)
+    lookup_config (bool& new_value,
+                   scope& rs,
+                   const string& var,
+                   uint64_t save_flags = 0)
     {
-      return lookup_config (new_value, rs, rs.ctx.var_pool[var]);
+      return lookup_config (new_value, rs, rs.ctx.var_pool[var], save_flags);
     }
 
     // Lookup a config.* variable value and, if the value is undefined, set it
diff --git a/libbuild2/config/utility.ixx b/libbuild2/config/utility.ixx
index 79d5470..d8348bd 100644
--- a/libbuild2/config/utility.ixx
+++ b/libbuild2/config/utility.ixx
@@ -6,22 +6,25 @@ namespace build2
   namespace config
   {
     LIBBUILD2_SYMEXPORT pair<lookup, bool>
-    lookup_config_impl (scope&, const variable&);
+    lookup_config_impl (scope&, const variable&, uint64_t);
 
     template <typename T>
     pair<lookup, bool>
     lookup_config_impl (scope&, const variable&, T&&, uint64_t, bool);
 
     inline lookup
-    lookup_config (scope& rs, const variable& var)
+    lookup_config (scope& rs, const variable& var, uint64_t sflags)
     {
-      return lookup_config_impl (rs, var).first;
+      return lookup_config_impl (rs, var, sflags).first;
     }
 
     inline lookup
-    lookup_config (bool& new_value, scope& rs, const variable& var)
+    lookup_config (bool& new_value,
+                   scope& rs,
+                   const variable& var,
+                   uint64_t sflags)
     {
-      auto r (lookup_config_impl (rs, var));
+      auto r (lookup_config_impl (rs, var, sflags));
       new_value = new_value || r.second;
       return r.first;
     }