solver: enforce conflicts during upgrades and new pkg installs

This makes sure any conflicted packages will be removed first.
Useful if we know there are conflicting files, and want to avoid
adding potentially harmful replaces line. Add a test case for
this too.

src/solver.c

@@ -762,11 +762,20 @@ static void cset_check_removal_by_iif(struct apk_solver_state *ss, struct apk_na
 static void cset_gen_name_change(struct apk_solver_state *ss, struct apk_name *name)
 {
 	struct apk_name **pname;
-	struct apk_package *pkg = name->ss.chosen.pkg, *opkg;
+	struct apk_package *pkg, *opkg;
 	struct apk_dependency *d;
 
-	if (pkg == NULL || pkg->ss.in_changeset)
+	if (name->ss.in_changeset) return;
+
+	pkg = name->ss.chosen.pkg;
+	if (pkg == NULL) {
+		/* Package removal */
+		opkg = name->ss.installed_pkg;
+		if (opkg) cset_gen_name_remove(ss, opkg);
+		name->ss.in_changeset = 1;
 		return;
+	}
+	if (pkg->ss.in_changeset) return;
 
 	pkg->ss.in_changeset = 1;
 	pkg->name->ss.in_changeset = 1;

test/upgrade.installed

+C:Q1EyN5AdpAOBJWKMR89pp/C66o+OE=
+P:libold
+V:1
+S:1
+I:1
+
+C:Q1eVpkasfqZAukAXFYbgwt4xAEEEe=
+P:app
+V:1
+S:1
+I:1
+D:libold
+

test/upgrade.repo

+C:Q1EyN5AdpAOBJWKMR89pp/C66o+OE=
+P:libold
+V:1
+S:1
+I:1
+
+C:Q1EyN5AdpAOBJWKMR89pp/C66o+FE=
+P:libnew
+V:1
+S:1
+I:1
+D:!libold
+
+C:Q1eVpkasfqZAukAXFYbgwt4xAEEEe=
+P:app
+V:1
+S:1
+I:1
+D:libold
+
+C:Q1EyN5AdpAOBJWKMR89pp/C77FFFF=
+P:app
+V:2
+S:1
+I:1
+D:libnew
+

test/upgrade1.test

+@ARGS
+--test-repo upgrade.repo
+--test-instdb upgrade.installed
+--test-world app
+upgrade
+@EXPECT
+(1/3) Purging libold (1)
+(2/3) Installing libnew (1)
+(3/3) Upgrading app (1 -> 2)
+OK: 0 MiB in 2 packages