Add container field to flag_declarations

A container is software which is always built in its entirety using the
same build environment. In particular, all of its parts are built using
the same build-time default flag values. In addition, containers are
always installed as a single unit.

Bug: 312696545
Test: atest aconfig.test && m all_aconfig_declarations
Change-Id: I2ef3db836c4456f4f4fb5c066edf9094e38f89cc

tools/aconfig/src/codegen.rs

@@ -38,6 +38,10 @@ pub fn is_valid_package_ident(s: &str) -> bool {
     s.split('.').all(is_valid_name_ident)
 }
 
+pub fn is_valid_container_ident(s: &str) -> bool {
+    is_valid_name_ident(s) || s.split('.').all(is_valid_name_ident)
+}
+
 pub fn create_device_config_ident(package: &str, flag_name: &str) -> Result<String> {
     ensure!(is_valid_package_ident(package), "bad package");
     ensure!(is_valid_name_ident(flag_name), "bad flag name");
@@ -84,6 +88,29 @@ mod tests {
         assert!(!is_valid_package_ident("foo.__bar"));
     }
 
+    #[test]
+    fn test_is_valid_container_ident() {
+        assert!(is_valid_container_ident("foo.bar"));
+        assert!(is_valid_container_ident("foo.bar_baz"));
+        assert!(is_valid_container_ident("foo.bar.a123"));
+        assert!(is_valid_container_ident("foo"));
+        assert!(is_valid_container_ident("foo_bar_123"));
+
+        assert!(!is_valid_container_ident(""));
+        assert!(!is_valid_container_ident("foo._bar"));
+        assert!(!is_valid_container_ident("_foo"));
+        assert!(!is_valid_container_ident("123_foo"));
+        assert!(!is_valid_container_ident("foo-bar"));
+        assert!(!is_valid_container_ident("foo-b\u{00e5}r"));
+        assert!(!is_valid_container_ident("foo.bar.123"));
+        assert!(!is_valid_container_ident(".foo.bar"));
+        assert!(!is_valid_container_ident("foo.bar."));
+        assert!(!is_valid_container_ident("."));
+        assert!(!is_valid_container_ident(".."));
+        assert!(!is_valid_container_ident("foo..bar"));
+        assert!(!is_valid_container_ident("foo.__bar"));
+    }
+
     #[test]
     fn test_create_device_config_ident() {
         assert_eq!(