aconfig: add read/write permission

Introduce the concept of flag read/write permissions: a read-only flag
can only have its value set during the build; a writable flag can by
updated in runtime.

Bug: 279485059
Test: atest aconfig.test
Change-Id: I3ec5c9571faa54de5666120ccd60090d3db9e331
diff --git a/tools/aconfig/src/aconfig.rs b/tools/aconfig/src/aconfig.rs
index 22fcb88..dc185f0 100644
--- a/tools/aconfig/src/aconfig.rs
+++ b/tools/aconfig/src/aconfig.rs
@@ -15,25 +15,46 @@
  */
 
 use anyhow::{anyhow, Context, Error, Result};
+use protobuf::{Enum, EnumOrUnknown};
+use serde::{Deserialize, Serialize};
 
 use crate::protos::{
-    ProtoAndroidConfig, ProtoFlag, ProtoOverride, ProtoOverrideConfig, ProtoValue,
+    ProtoAndroidConfig, ProtoFlag, ProtoOverride, ProtoOverrideConfig, ProtoPermission, ProtoValue,
 };
 
+#[derive(Debug, PartialEq, Eq, Serialize, Deserialize, Clone, Copy)]
+pub enum Permission {
+    ReadOnly,
+    ReadWrite,
+}
+
+impl TryFrom<EnumOrUnknown<ProtoPermission>> for Permission {
+    type Error = Error;
+
+    fn try_from(proto: EnumOrUnknown<ProtoPermission>) -> Result<Self, Self::Error> {
+        match ProtoPermission::from_i32(proto.value()) {
+            Some(ProtoPermission::READ_ONLY) => Ok(Permission::ReadOnly),
+            Some(ProtoPermission::READ_WRITE) => Ok(Permission::ReadWrite),
+            None => Err(anyhow!("unknown permission enum value {}", proto.value())),
+        }
+    }
+}
+
 #[derive(Debug, PartialEq, Eq)]
 pub struct Value {
     value: bool,
+    permission: Permission,
     since: Option<u32>,
 }
 
 #[allow(dead_code)] // only used in unit tests
 impl Value {
-    pub fn new(value: bool, since: u32) -> Value {
-        Value { value, since: Some(since) }
+    pub fn new(value: bool, permission: Permission, since: u32) -> Value {
+        Value { value, permission, since: Some(since) }
     }
 
-    pub fn default(value: bool) -> Value {
-        Value { value, since: None }
+    pub fn default(value: bool, permission: Permission) -> Value {
+        Value { value, permission, since: None }
     }
 }
 
@@ -44,7 +65,11 @@
         let Some(value) = proto.value else {
             return Err(anyhow!("missing 'value' field"));
         };
-        Ok(Value { value, since: proto.since })
+        let Some(proto_permission) = proto.permission else {
+            return Err(anyhow!("missing 'permission' field"));
+        };
+        let permission = proto_permission.try_into()?;
+        Ok(Value { value, permission, since: proto.since })
     }
 }
 
@@ -72,15 +97,17 @@
         proto.flag.into_iter().map(|proto_flag| proto_flag.try_into()).collect()
     }
 
-    pub fn resolve_value(&self, build_id: u32) -> bool {
+    pub fn resolve(&self, build_id: u32) -> (bool, Permission) {
         let mut value = self.values[0].value;
+        let mut permission = self.values[0].permission;
         for candidate in self.values.iter().skip(1) {
             let since = candidate.since.expect("invariant: non-defaults values have Some(since)");
             if since <= build_id {
                 value = candidate.value;
+                permission = candidate.permission;
             }
         }
-        value
+        (value, permission)
     }
 }
 
@@ -120,6 +147,7 @@
 pub struct Override {
     pub id: String,
     pub value: bool,
+    pub permission: Permission,
 }
 
 impl Override {
@@ -145,7 +173,11 @@
         let Some(value) = proto.value else {
             return Err(anyhow!("missing 'value' field"));
         };
-        Ok(Override { id, value })
+        let Some(proto_permission) = proto.permission else {
+            return Err(anyhow!("missing 'permission' field"));
+        };
+        let permission = proto_permission.try_into()?;
+        Ok(Override { id, value, permission })
     }
 }
 
@@ -158,7 +190,10 @@
         let expected = Flag {
             id: "1234".to_owned(),
             description: "Description of the flag".to_owned(),
-            values: vec![Value::default(false), Value::new(true, 8)],
+            values: vec![
+                Value::default(false, Permission::ReadOnly),
+                Value::new(true, Permission::ReadWrite, 8),
+            ],
         };
 
         let s = r#"
@@ -166,9 +201,11 @@
         description: "Description of the flag"
         value {
             value: false
+            permission: READ_ONLY
         }
         value {
             value: true
+            permission: READ_WRITE
             since: 8
         }
         "#;
@@ -190,6 +227,7 @@
         description: "Description of the flag"
         value {
             value: true
+            permission: READ_ONLY
         }
         "#;
         let error = Flag::try_from_text_proto(s).unwrap_err();
@@ -200,9 +238,11 @@
         description: "Description of the flag"
         value {
             value: true
+            permission: READ_ONLY
         }
         value {
             value: true
+            permission: READ_ONLY
         }
         "#;
         let error = Flag::try_from_text_proto(s).unwrap_err();
@@ -215,12 +255,12 @@
             Flag {
                 id: "a".to_owned(),
                 description: "A".to_owned(),
-                values: vec![Value::default(true)],
+                values: vec![Value::default(true, Permission::ReadOnly)],
             },
             Flag {
                 id: "b".to_owned(),
                 description: "B".to_owned(),
-                values: vec![Value::default(false)],
+                values: vec![Value::default(false, Permission::ReadWrite)],
             },
         ];
 
@@ -230,6 +270,7 @@
             description: "A"
             value {
                 value: true
+                permission: READ_ONLY
             }
         }
         flag {
@@ -237,6 +278,7 @@
             description: "B"
             value {
                 value: false
+                permission: READ_WRITE
             }
         }
         "#;
@@ -247,11 +289,13 @@
 
     #[test]
     fn test_override_try_from_text_proto_list() {
-        let expected = Override { id: "1234".to_owned(), value: true };
+        let expected =
+            Override { id: "1234".to_owned(), value: true, permission: Permission::ReadOnly };
 
         let s = r#"
         id: "1234"
         value: true
+        permission: READ_ONLY
         "#;
         let actual = Override::try_from_text_proto(s).unwrap();
 
@@ -259,26 +303,26 @@
     }
 
     #[test]
-    fn test_resolve_value() {
+    fn test_flag_resolve() {
         let flag = Flag {
             id: "a".to_owned(),
             description: "A".to_owned(),
             values: vec![
-                Value::default(true),
-                Value::new(false, 10),
-                Value::new(true, 20),
-                Value::new(false, 30),
+                Value::default(false, Permission::ReadOnly),
+                Value::new(false, Permission::ReadWrite, 10),
+                Value::new(true, Permission::ReadOnly, 20),
+                Value::new(true, Permission::ReadWrite, 30),
             ],
         };
-        assert!(flag.resolve_value(0));
-        assert!(flag.resolve_value(9));
-        assert!(!flag.resolve_value(10));
-        assert!(!flag.resolve_value(11));
-        assert!(!flag.resolve_value(19));
-        assert!(flag.resolve_value(20));
-        assert!(flag.resolve_value(21));
-        assert!(flag.resolve_value(29));
-        assert!(!flag.resolve_value(30));
-        assert!(!flag.resolve_value(10_000));
+        assert_eq!((false, Permission::ReadOnly), flag.resolve(0));
+        assert_eq!((false, Permission::ReadOnly), flag.resolve(9));
+        assert_eq!((false, Permission::ReadWrite), flag.resolve(10));
+        assert_eq!((false, Permission::ReadWrite), flag.resolve(11));
+        assert_eq!((false, Permission::ReadWrite), flag.resolve(19));
+        assert_eq!((true, Permission::ReadOnly), flag.resolve(20));
+        assert_eq!((true, Permission::ReadOnly), flag.resolve(21));
+        assert_eq!((true, Permission::ReadOnly), flag.resolve(29));
+        assert_eq!((true, Permission::ReadWrite), flag.resolve(30));
+        assert_eq!((true, Permission::ReadWrite), flag.resolve(10_000));
     }
 }