From 026c827b978761bf0cb618ff9429df8508cd3190 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 19 May 2022 13:10:54 +0200
Subject: Make $config.origin() also available internally as config::origin()

---
 libbuild2/config/functions.cxx | 38 ++++++++++----------------------------
 libbuild2/config/utility.cxx   | 33 +++++++++++++++++++++++++++++++++
 libbuild2/config/utility.hxx   | 16 ++++++++++++++++
 3 files changed, 59 insertions(+), 28 deletions(-)

diff --git a/libbuild2/config/functions.cxx b/libbuild2/config/functions.cxx
index 3e1b8a3..84c1b03 100644
--- a/libbuild2/config/functions.cxx
+++ b/libbuild2/config/functions.cxx
@@ -23,8 +23,8 @@ namespace build2
 
       // $config.origin()
       //
-      // Return the origin of the specified configuration variable value.
-      // Possible result values and their semantics are as follows:
+      // Return the origin of the value of the specified configuration
+      // variable. Possible result values and their semantics are as follows:
       //
       // undefined
       //    The variable is undefined.
@@ -60,33 +60,15 @@ namespace build2
         if (s == nullptr)
           fail << "config.origin() called out of project" << endf;
 
-        string n (convert<string> (move (name)));
+        switch (origin (*s, convert<string> (move (name))).first)
+        {
+        case variable_origin::undefined: return "undefined";
+        case variable_origin::default_:  return "default";
+        case variable_origin::buildfile: return "buildfile";
+        case variable_origin::override_: return "override";
+        }
 
-        // Make sure this is a config.* variable. This could matter since we
-        // reply on the semantics of value::extra. We could also detect
-        // special variables like config.booted, some config.config.*, etc.,
-        // (see config_save() for details) but that seems harmless.
-        //
-        if (n.compare (0, 7, "config.") != 0)
-          fail << "non-config.* variable passed to config.origin()" << endf;
-
-        const variable* var (s->ctx.var_pool.find (n));
-
-        if (var == nullptr)
-          return "undefined";
-
-        pair<lookup, size_t> org (s->lookup_original (*var));
-        pair<lookup, size_t> ovr (var->overrides == nullptr
-                                  ? org
-                                  : s->lookup_override (*var, org));
-
-        if (!ovr.first.defined ())
-          return "undefined";
-
-        if (org.first != ovr.first)
-          return "override";
-
-        return org.first->extra ? "default" : "buildfile";
+        return ""; // Should not reach.
       };
 
       // $config.save()
diff --git a/libbuild2/config/utility.cxx b/libbuild2/config/utility.cxx
index a78b263..7437c5b 100644
--- a/libbuild2/config/utility.cxx
+++ b/libbuild2/config/utility.cxx
@@ -156,5 +156,38 @@ namespace build2
       else
         return false;
     }
+
+    pair<variable_origin, lookup>
+    origin (const scope& rs, const string& n)
+    {
+      // Make sure this is a config.* variable. This could matter since we
+      // reply on the semantics of value::extra. We could also detect
+      // special variables like config.booted, some config.config.*, etc.,
+      // (see config_save() for details) but that seems harmless.
+      //
+      if (n.compare (0, 7, "config.") != 0)
+        throw invalid_argument ("config.* variable expected");
+
+      const variable* var (rs.ctx.var_pool.find (n));
+
+      if (var == nullptr)
+        return make_pair (variable_origin::undefined, lookup ());
+
+      pair<lookup, size_t> org (rs.lookup_original (*var));
+      pair<lookup, size_t> ovr (var->overrides == nullptr
+                                ? org
+                                : rs.lookup_override (*var, org));
+
+      if (!ovr.first.defined ())
+        return make_pair (variable_origin::undefined, lookup ());
+
+      if (org.first != ovr.first)
+        return make_pair (variable_origin::override_, ovr.first);
+
+      return make_pair (org.first->extra
+                        ? variable_origin::default_
+                        : variable_origin::buildfile,
+                        org.first);
+    }
   }
 }
diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index cb82ea6..5a00d00 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -501,6 +501,22 @@ namespace build2
     //
     LIBBUILD2_SYMEXPORT bool
     unconfigured (scope& rs, const string& var, bool value);
+
+    // Return the origin of the value of the specified configuration variable
+    // plus the value itself. See $config.origin() for details.
+    //
+    // Throws invalid_argument if the passed variable is not config.*.
+    //
+    enum class variable_origin
+    {
+      undefined,  // Undefined.
+      default_,   // Default value from the config directive.
+      buildfile,  // Value from a buildfile, normally config.build.
+      override_   // Value from a command line override.
+    };
+
+    LIBBUILD2_SYMEXPORT pair<variable_origin, lookup>
+    origin (const scope& rs, const string& name);
   }
 }
 
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