From b679b1452d6513c0769928a2238ccd367c2b78f7 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Tue, 31 Mar 2020 08:07:02 +0200
Subject: Handle duplicate config directives for same variable

---
 libbuild2/config/utility.hxx      |  3 ++-
 libbuild2/parser.cxx              | 19 ++++++++++++++++++-
 tests/directive/config.testscript | 10 +++++++++-
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index f2bddc2..38a3ae1 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -99,7 +99,8 @@ namespace build2
     // then, if there is no value, call the version with the default value and
     // end up with the same result if we called the default value version
     // straight away. This is useful when computing the default value is
-    // expensive.
+    // 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.
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index 532b357..797a484 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -1885,7 +1885,24 @@ namespace build2
 
       if (l.var != nullptr)
       {
-        config_report.push_back (make_pair (l, move (*report)));
+        auto r (make_pair (l, move (*report)));
+
+        // If we have a duplicate, update it (it could be useful to have
+        // multiple config directives to "probe" the value before calculating
+        // the default; see lookup_config() for details).
+        //
+        auto i (find_if (config_report.begin (),
+                         config_report.end (),
+                         [&l] (const pair<lookup, string>& p)
+                         {
+                           return p.first.var == l.var;
+                         }));
+
+        if (i == config_report.end ())
+          config_report.push_back (move (r));
+        else
+          *i = move (r);
+
         config_report_new = config_report_new || new_val;
       }
     }
diff --git a/tests/directive/config.testscript b/tests/directive/config.testscript
index f77a098..e84ca0a 100644
--- a/tests/directive/config.testscript
+++ b/tests/directive/config.testscript
@@ -180,6 +180,8 @@ test.arguments =
     config [string,  config.report.variable=e] config.test.e ?= abc
     config [         config.report]            f
     config [bool]                              config.test.n ?= [null]
+    config [bool]                              config.test.p
+    config [bool]                              config.test.p ?= true
 
     e = "'$config.test.e'"
     f = ($config.test.b || $config.test.c)
@@ -206,11 +208,16 @@ test.arguments =
       e          'abc'
       f          true
       n          [null]
+      p          true
     EOO
 
   # Configured.
   #
-  $* configure config.test.a=true config.test.e=xyz config.test.n=true;
+  $* configure          \
+     config.test.a=true \
+     config.test.e=xyz  \
+     config.test.n=true \
+     config.test.p=false;
   $* noop -v;
   $* noop -V 2>>~/EOO/;
     /config test@.+/
@@ -223,6 +230,7 @@ test.arguments =
       e          'xyz'
       f          true
       n          true
+      p          false
     EOO
   $* disfigure
 }
-- 
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