fix lock merge of lockfiles with alias (#13763)

Changelog: Bugfix: Fix ``conan lock merge`` of lockfiles containing
alias
Docs: Omit

Coming from #13597

conans/model/graph_lock.py

@@ -146,6 +146,7 @@ def merge(self, other):
         self._requires.merge(other._requires)
         self._build_requires.merge(other._build_requires)
         self._python_requires.merge(other._python_requires)
+        self._alias.update(other._alias)
 
     def add(self, requires=None, build_requires=None, python_requires=None):
         """ adding new things manually will trigger the sort() of the locked list, so lockfiles

conans/test/integration/lockfile/test_lock_alias.py

@@ -1,5 +1,4 @@
 import os
-import textwrap
 
 import pytest
 

conans/test/integration/lockfile/test_lock_merge.py

@@ -0,0 +1,59 @@
+import textwrap
+
+import pytest
+
+from conans.test.assets.genconanfile import GenConanfile
+from conans.test.utils.tools import TestClient
+
+
+@pytest.mark.parametrize("requires", ["requires", "tool_requires"])
+def test_merge_alias(requires):
+    """
+    basic lockfile merging including alias
+    """
+    c = TestClient()
+    app = textwrap.dedent(f"""
+        from conan import ConanFile
+        class App(ConanFile):
+            settings = "build_type"
+            def requirements(self):
+                if self.settings.build_type == "Debug":
+                    self.{requires}("pkg/(alias_debug)")
+                else:
+                    self.{requires}("pkg/(alias_release)")
+        """)
+    c.save({"pkg/conanfile.py": GenConanfile("pkg"),
+            "alias_release/conanfile.py": GenConanfile("pkg", "alias_release").with_class_attribute(
+                "alias = 'pkg/0.1'"),
+            "alias_debug/conanfile.py": GenConanfile("pkg", "alias_debug").with_class_attribute(
+                "alias = 'pkg/0.2'"),
+            "app/conanfile.py": app})
+    c.run("create pkg --version=0.1")
+    c.run("create pkg --version=0.2")
+    c.run("export alias_release")
+    c.run("export alias_debug")
+    c.run("lock create app -s build_type=Release --lockfile-out=release.lock")
+    c.run("lock create app -s build_type=Debug --lockfile-out=debug.lock")
+
+    c.run("lock merge --lockfile=release.lock --lockfile=debug.lock --lockfile-out=conan.lock")
+
+    # Update alias, won't be used
+    c.save({"alias_release/conanfile.py": GenConanfile("pkg", "alias_release").with_class_attribute(
+                "alias = 'pkg/0.3'"),
+            "alias_debug/conanfile.py": GenConanfile("pkg", "alias_debug").with_class_attribute(
+                "alias = 'pkg/0.4'")})
+    c.run("export alias_release")
+    c.run("export alias_debug")
+
+    # Merged one can resolve both aliased without issues
+    c.run("install app -s build_type=Release --lockfile=conan.lock")
+    is_build_requires = requires == "tool_requires"
+    c.assert_listed_require({"pkg/0.1": "Cache"}, build=is_build_requires)
+    c.run("install app -s build_type=Debug --lockfile=conan.lock")
+    c.assert_listed_require({"pkg/0.2": "Cache"}, build=is_build_requires)
+
+    # without lockfiles it would be pointing to the new (unexistent) ones
+    c.run("install app -s build_type=Release", assert_error=True)
+    assert "ERROR: Package 'pkg/0.3' not resolved" in c.out
+    c.run("install app -s build_type=Debug", assert_error=True)
+    assert "ERROR: Package 'pkg/0.4' not resolved" in c.out