From 50a5c7b14250dab7941e8b0a67dfe6c442d2c5a9 Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Tue, 29 Jun 2021 19:11:26 +0300
Subject: Fix selection of build entry between two in pkg-build

---
 bpkg/pkg-build.cxx          | 18 +++++++++++-----
 tests/pkg-build.testscript  | 50 +++++++++++++++++++++++++++++++++++++++++++--
 tests/pkg-system.testscript |  4 ++--
 3 files changed, 63 insertions(+), 9 deletions(-)

diff --git a/bpkg/pkg-build.cxx b/bpkg/pkg-build.cxx
index 32a680f..1e80d1e 100644
--- a/bpkg/pkg-build.cxx
+++ b/bpkg/pkg-build.cxx
@@ -604,12 +604,20 @@ namespace bpkg
           {
             using constraint_type = build_package::constraint_type;
 
-            // If the versions differ, we have to pick one. Start with the
-            // newest version since if both satisfy, then that's the one we
-            // should prefer. So get the first to try into p1 and the second
-            // to try -- into p2.
+            // If the versions differ, we have to pick one. Pick with the
+            // following preference order: user selection over implicit one,
+            // source package over a system one, newer version over an older
+            // one. So get the preferred to try into p1 and the other to try
+            // -- into p2.
             //
-            if (p2->available_version () > p1->available_version ())
+            int us (p1->user_selection () - p2->user_selection ());
+            int sf (p1->system - p2->system);
+
+            if (us < 0              ||
+                (us == 0 && sf > 0) ||
+                (us == 0 &&
+                 sf == 0 &&
+                 p2->available_version () > p1->available_version ()))
               swap (p1, p2);
 
             // See if pv's version satisfies pc's constraints. Return the
diff --git a/tests/pkg-build.testscript b/tests/pkg-build.testscript
index 50db679..64e6af8 100644
--- a/tests/pkg-build.testscript
+++ b/tests/pkg-build.testscript
@@ -746,10 +746,10 @@ test.options += --no-progress
     $clone_cfg;
     $* libfoo/1.0.0 libbaz 2>>EOE != 0
       error: unable to satisfy constraints on package libfoo
-        info: libbar depends on (libfoo == 1.1.0)
         info: command line depends on (libfoo == 1.0.0)
-        info: available libfoo/1.1.0
+        info: libbar depends on (libfoo == 1.1.0)
         info: available libfoo/1.0.0
+        info: available libfoo/1.1.0
         info: explicitly specify libfoo version to manually satisfy both constraints
       info: while satisfying libbar/1.1.0
       info: while satisfying libbaz/1.1.0
@@ -2170,6 +2170,52 @@ test.options += --no-progress
 
         $pkg_drop libbar
       }
+
+      : sys-to-src-unhold
+      :
+      {
+        $clone_cfg;
+
+        $* 'sys:libbaz/1.2.0' 2>>EOE;
+          configured sys:libbaz/1.2.0
+          EOE
+
+        $* ?libbaz libbar/0.0.3 2>>EOE;
+          purged libbaz/1.2.0
+          fetched libbaz/0.1.0
+          unpacked libbaz/0.1.0
+          fetched libbar/0.0.3
+          unpacked libbar/0.0.3
+          configured libbaz/0.1.0
+          configured libbar/0.0.3
+          EOE
+
+        $pkg_drop libbar libbaz
+      }
+
+      : sys-to-src
+      :
+      : As above but keep held.
+      :
+      {
+        $clone_cfg;
+
+        $* 'sys:libbaz/1.2.0' 2>>EOE;
+          configured sys:libbaz/1.2.0
+          EOE
+
+        $* libbaz libbar/0.0.3 2>>EOE;
+          purged libbaz/1.2.0
+          fetched libbaz/0.1.0
+          unpacked libbaz/0.1.0
+          fetched libbar/0.0.3
+          unpacked libbar/0.0.3
+          configured libbaz/0.1.0
+          configured libbar/0.0.3
+          EOE
+
+        $pkg_drop libbar libbaz
+      }
     }
 
     : source
diff --git a/tests/pkg-system.testscript b/tests/pkg-system.testscript
index 26d6893..3ff1b55 100644
--- a/tests/pkg-system.testscript
+++ b/tests/pkg-system.testscript
@@ -711,10 +711,10 @@ rep_remove += -d cfg 2>!
     #
     $pkg_build foo 'sys:libbar/1' 2>>EOE != 0;
       error: unable to satisfy constraints on package libbar
-        info: foo depends on (libbar >= 2)
         info: command line depends on (libbar == 1)
-        info: available sys:libbar/2
+        info: foo depends on (libbar >= 2)
         info: available sys:libbar/1
+        info: available sys:libbar/2
         info: explicitly specify libbar version to manually satisfy both constraints
       info: while satisfying foo/2
       EOE
-- 
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