Support generation of flag attribute in java_cpp_enum.py

RefreshType in task_manager_observer.h is a real example of the enums
needing this handling. Unless we generate it with the flag attribute,
we can't concatenate the constants with `|`, seeing the error like this:

```
../../chrome/browser/task_manager/internal/android/java/src/org/chromium/chrome/browser/task_manager/TaskManagerActivity.java:32: Error: Flag not allowed here [WrongConstant]
                        observer, REFRESH_TIME_MS, RefreshType.MEMORY_FOOTPRINT | RefreshType.CPU);
```

Bug: 353596679
Change-Id: I382678b39dd9ff85e619cc1881eb087b463d22bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6034170
Auto-Submit: Keigo Oka <oka@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1384981}

build/android/gyp/java_cpp_enum.py

@@ -32,8 +32,15 @@ ENUM_FIXED_TYPE_ALLOWLIST = [
 
 
 class EnumDefinition:
-  def __init__(self, original_enum_name=None, class_name_override=None,
-               enum_package=None, entries=None, comments=None, fixed_type=None):
+
+  def __init__(self,
+               original_enum_name=None,
+               class_name_override=None,
+               enum_package=None,
+               entries=None,
+               comments=None,
+               fixed_type=None,
+               is_flag=False):
     self.original_enum_name = original_enum_name
     self.class_name_override = class_name_override
     self.enum_package = enum_package
@@ -41,6 +48,7 @@ class EnumDefinition:
     self.comments = collections.OrderedDict(comments or [])
     self.prefix_to_strip = None
     self.fixed_type = fixed_type
+    self.is_flag = is_flag
 
   def AppendEntry(self, key, value):
     if key in self.entries:
@@ -148,8 +156,11 @@ class DirectiveSet:
   class_name_override_key = 'CLASS_NAME_OVERRIDE'
   enum_package_key = 'ENUM_PACKAGE'
   prefix_to_strip_key = 'PREFIX_TO_STRIP'
+  is_flag = 'IS_FLAG'
 
-  known_keys = [class_name_override_key, enum_package_key, prefix_to_strip_key]
+  known_keys = [
+      class_name_override_key, enum_package_key, prefix_to_strip_key, is_flag
+  ]
 
   def __init__(self):
     self._directives = {}
@@ -170,6 +181,8 @@ class DirectiveSet:
         DirectiveSet.enum_package_key)
     definition.prefix_to_strip = self._directives.get(
         DirectiveSet.prefix_to_strip_key)
+    definition.is_flag = self._directives.get(
+        DirectiveSet.is_flag) not in [None, 'false', '0']
 
 
 class HeaderParser:
@@ -398,7 +411,7 @@ import androidx.annotation.IntDef;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 
-@IntDef({
+@IntDef(${FLAG_DEF}{
 ${INT_DEF}
 })
 @Retention(RetentionPolicy.SOURCE)
@@ -441,10 +454,11 @@ ${ENUM_ENTRIES}
       'CLASS_NAME': enum_definition.class_name,
       'ENUM_ENTRIES': enum_entries_string,
       'PACKAGE': enum_definition.enum_package,
+      'FLAG_DEF': 'flag = true, value = ' if enum_definition.is_flag else '',
       'INT_DEF': enum_names_string,
       'SCRIPT_NAME': java_cpp_utils.GetScriptName(),
       'SOURCE_PATH': source_path,
-      'YEAR': str(date.today().year)
+      'YEAR': str(date.today().year),
   }
   return template.substitute(values)
 

build/android/gyp/java_cpp_enum_tests.py

@@ -86,6 +86,35 @@ public @interface ClassName {
                                               ('VALUE_ONE', 1)]),
                      definition.entries)
 
+  def testOutputFlag(self):
+    for [attr, want_flag] in [
+        ['0', False],
+        ['1', True],
+        ['false', False],
+        ['true', True],
+    ]:
+      test_data = ("""
+        // GENERATED_JAVA_ENUM_PACKAGE: test.namespace
+        // GENERATED_JAVA_IS_FLAG: %s
+        enum EnumName {
+          ZERO = 1 << 0,
+          ONE = 1 << 1,
+        };
+      """ % attr).split('\n')
+      definitions = HeaderParser(test_data).ParseDefinitions()
+      output = GenerateOutput('/path/to/file', definitions[0])
+      int_def = output[output.index("@IntDef"):]
+      expected = """@IntDef(%s{
+    EnumName.ZERO, EnumName.ONE
+})
+@Retention(RetentionPolicy.SOURCE)
+public @interface EnumName {
+  int ZERO = 1 << 0;
+  int ONE = 1 << 1;
+}
+""" % ('flag = true, value = ' if want_flag else '')
+      self.assertEqual(int_def, expected)
+
   def testParseBitShifts(self):
     test_data = """
       // GENERATED_JAVA_ENUM_PACKAGE: test.namespace

docs/android_accessing_cpp_enums_in_java.md

@@ -20,6 +20,7 @@ directive (optional)
 the `GENERATED_JAVA_PREFIX_TO_STRIP` directive (optional)
 * Follows best practices by using
 [IntDef Instead of Enum](/styleguide/java/java.md#IntDef-Instead-of-Enum)
+* Generate the `flag` attribute using the `GENERATED_JAVA_IS_FLAG` directive (optional)
 * Copies comments that directly precede enum entries into the generated Java
 class
 
@@ -32,9 +33,10 @@ class
     // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.chrome
     // GENERATED_JAVA_CLASS_NAME_OVERRIDE: FooBar
     // GENERATED_JAVA_PREFIX_TO_STRIP: BAR_
+    // GENERATED_JAVA_IS_FLAG: true
     enum SomeEnum {
-      BAR_A,
-      BAR_B,
+      BAR_A = 1 << 0,
+      BAR_B = 1 << 1,
       BAR_C = BAR_B,
     };
     ```
@@ -80,14 +82,14 @@ class
     import java.lang.annotation.Retention;
     import java.lang.annotation.RetentionPolicy;
 
-    @IntDef({
+    @IntDef(flag = true, value = {
         FooBar.A, FooBar.B, FooBar.C
     })
     @Retention(RetentionPolicy.SOURCE)
     public @interface FooBar {
-      int A = 0;
-      int B = 1;
-      int C = 1;
+      int A = 1 << 0;
+      int B = 1 << 1;
+      int C = 1 << 1;
     }
     ```