Verify --channel is not passed without --user (#14443)

conan/cli/args.py

@@ -126,6 +126,8 @@ def validate_common_graph_args(args):
     if args.requires and (args.name or args.version or args.user or args.channel):
         raise ConanException("Can't use --name, --version, --user or --channel arguments with "
                              "--requires")
+    if args.channel and not args.user:
+        raise ConanException("Can't specify --channel without --user")
     if not args.path and not args.requires and not args.tool_requires:
         raise ConanException("Please specify a path to a conanfile or a '--requires=<ref>'")
     if args.path and (args.requires or args.tool_requires):

conans/test/integration/command/install/install_test.py

@@ -29,6 +29,9 @@ def test_install_reference_error(client):
     # Test to check the "conan install <path> <reference>" command argument
     client.run("install --requires=pkg/0.1@myuser/testing --user=user --channel=testing", assert_error=True)
     assert "ERROR: Can't use --name, --version, --user or --channel arguments with --requires" in client.out
+    client.save({"conanfile.py": GenConanfile("pkg", "1.0")})
+    client.run("install . --channel=testing", assert_error=True)
+    assert "ERROR: Can't specify --channel without --user" in client.out
 
 
 def test_install_args_error():