solver: only select a default if there is at least one provider with a declared provider_priority

src/solver.c

@@ -668,6 +668,12 @@ static void select_package(struct apk_solver_state *ss, struct apk_name *name)
 			    (!p->pkg->ss.iif_triggered ||
 			     !p->pkg->ss.tag_ok))
 				continue;
+			/* Virtual packages without provider_priority cannot be autoselected */
+			if (p->version == &apk_null_blob &&
+			    p->pkg->name->auto_select_virtual == 0 &&
+			    p->pkg->name->ss.requirers == 0 &&
+			    p->pkg->provider_priority == 0)
+				continue;
 			if (compare_providers(ss, p, &chosen) > 0)
 				chosen = *p;
 		}

test/provides.repo

@@ -38,6 +38,7 @@ V:1
 S:1
 I:1
 p:mail-reader
+k:1
 
 C:Q1eVpkasfqZAukAXFYbgwt4xAEEEe=
 P:mailreadplus
@@ -45,7 +46,7 @@ V:1
 S:1
 I:1
 p:mail-reader
-k:1
+k:2
 
 C:Q1EyN5AdpAOBJWKMR89pp/C77FFFF=
 P:server-a
@@ -68,3 +69,17 @@ S:1
 I:1
 p:selfprovided=2
 p:selfprovided=3
+
+C:Q1EyN5AdpAOBJWKMR89ppC66aaaaj=
+P:conflicted-provider-a
+V:0.1
+S:1
+I:1
+p:conflicted-provider
+
+C:Q1EyN5AdpAOBJWKMR89ppC66bbbbj=
+P:conflicted-provider-b
+V:0.1
+S:1
+I:1
+p:conflicted-provider

test/provides9.test

+@ARGS
+--test-repo provides.repo
+add conflicted-provider
+@EXPECT
+ERROR: unsatisfiable constraints:
+  conflicted-provider (virtual):
+    provided by: conflicted-provider-a
+                 conflicted-provider-b
+    required by: world[conflicted-provider]