pw_protobuf: Generate kValue-style aliases for enum cases

To make pw_protobuf code more beautiful at the point of use, generate
aliases for enum cases that match the kValue style, with common prefixes
removed.

e.g. given

  enum State {
    STATE_UNKNOWN = 0;
    STATE_OFF = 1;
    STATE_ON = 2;
  };

in addition to the basic enum class generated:

  enum class State {
    STATE_UNKNOWN = 0,
    STATE_OFF = 1,
    STATE_ON = 2

it will also generate:

    kUnknown = STATE_UNKNOWN,
    kOff = STATE_OFF,
    kOn = STATE_ON
  };

Change-Id: Ifff30034cffce52cdee665320bc24a08fec72194
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/92042
Pigweed-Auto-Submit: Scott James Remnant <keybuk@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Keir Mierle <keir@google.com>

pw_protobuf/codegen_message_test.cc

@@ -1605,6 +1605,21 @@ TEST(CodegenMessage, WriteNestedForcedCallback) {
             0);
 }
 
+TEST(CodegenMessage, EnumAliases) {
+  // Unprefixed enum.
+  EXPECT_EQ(Bool::kTrue, Bool::TRUE);
+  EXPECT_EQ(Bool::kFalse, Bool::FALSE);
+  EXPECT_EQ(Bool::kFileNotFound, Bool::FILE_NOT_FOUND);
+
+  // Prefixed enum has the prefix removed.
+  EXPECT_EQ(Error::kNone, Error::ERROR_NONE);
+  EXPECT_EQ(Error::kNotFound, Error::ERROR_NOT_FOUND);
+  EXPECT_EQ(Error::kUnknown, Error::ERROR_UNKNOWN);
+
+  // Single-value enum.
+  EXPECT_EQ(AlwaysBlue::kBlue, AlwaysBlue::BLUE);
+}
+
 class BreakableEncoder : public KeyValuePair::MemoryEncoder {
  public:
   constexpr BreakableEncoder(ByteSpan buffer)

pw_protobuf/docs.rst

@@ -65,7 +65,11 @@ This results in the following generated structure:
   enum class Customer::Status {
     NEW = 1,
     ACTIVE = 2,
-    INACTIVE = 3
+    INACTIVE = 3,
+
+    kNew = NEW,
+    kActive = ACTIVE,
+    kInactive = INACTIVE,
   };
 
   struct Customer::Message {
@@ -498,10 +502,45 @@ that can hold the set of values encoded by it, following these rules.
 
   .. code:: c++
 
+    enum class Award::Service {
+      BRONZE = 1,
+      SILVER = 2,
+      GOLD = 3,
+
+      kBronze = BRONZE,
+      kSilver = SILVER,
+      kGold = GOLD,
+    };
+
     struct Award::Message {
       Award::Service service;
     };
 
+  Aliases to the enum values are also included in the "constant" style to match
+  your preferred coding style. These aliases have any common prefix to the
+  enumeration values removed, such that:
+
+  .. code::
+
+    enum Activity {
+      ACTIVITY_CYCLING = 1;
+      ACTIVITY_RUNNING = 2;
+      ACTIVITY_SWIMMING = 3;
+    }
+
+  .. code:: c++
+
+    enum class Activity {
+      ACTIVITY_CYCLING = 1,
+      ACTIVITY_RUNNING = 2,
+      ACTIVITY_SWIMMING = 3,
+
+      kCycling = ACTIVITY_CYCLING,
+      kRunning = ACTIVITY_RUNNING,
+      kSwimming = ACTIVITY_SWIMMING,
+    };
+
+
 * Nested messages are represented by their own ``struct Message`` provided that
   a reference cycle does not exist.
 

pw_protobuf/pw_protobuf_test_protos/full_test.proto

@@ -24,6 +24,16 @@ enum Bool {
   FILE_NOT_FOUND = 2;
 }
 
+// Prefixed enum
+enum Error {
+  ERROR_NONE = 0;
+  ERROR_NOT_FOUND = 1;
+  ERROR_UNKNOWN = 2;
+}
+
+// Single-value enum
+enum AlwaysBlue { BLUE = 0; }
+
 // A message!
 message Pigweed {
   // Nested messages and enums.

pw_protobuf/py/pw_protobuf/codegen_pwpb.py

@@ -18,6 +18,7 @@
 import enum
 # Type ignore here for graphlib-backport on Python 3.8
 from graphlib import CycleError, TopologicalSorter  # type: ignore
+from itertools import takewhile
 import os
 import sys
 from typing import Dict, Iterable, List, Tuple
@@ -1815,16 +1816,55 @@ def define_not_in_class_methods(message: ProtoMessage, root: ProtoNode,
             output.write_line('}')
 
 
+def _common_value_prefix(proto_enum: ProtoEnum) -> str:
+    """Calculate the common prefix of all enum values.
+
+    Given an enumeration:
+        enum Thing {
+            THING_ONE = 1;
+            THING_TWO = 2;
+            THING_THREE = 3;
+        }
+
+    If will return 'THING_', resulting in generated "style" aliases of
+    'kOne', 'kTwo', and 'kThree'.
+
+    The prefix is walked back to the last _, so that the enumeration:
+        enum Activity {
+            ACTIVITY_RUN = 1;
+            ACTIVITY_ROW = 2;
+        }
+
+    Returns 'ACTIVITY_' and not 'ACTIVITY_R'.
+    """
+    if len(proto_enum.values()) <= 1:
+        return ''
+
+    common_prefix = "".join(
+        ch[0]
+        for ch in takewhile(lambda ch: all(ch[0] == c for c in ch),
+                            zip(*[name for name, _ in proto_enum.values()])))
+    (left, under, _) = common_prefix.rpartition('_')
+    return left + under
+
+
 def generate_code_for_enum(proto_enum: ProtoEnum, root: ProtoNode,
                            output: OutputFile) -> None:
     """Creates a C++ enum for a proto enum."""
     assert proto_enum.type() == ProtoNode.Type.ENUM
 
+    common_prefix = _common_value_prefix(proto_enum)
     output.write_line(f'enum class {proto_enum.cpp_namespace(root)} '
                       f': uint32_t {{')
     with output.indent():
         for name, number in proto_enum.values():
             output.write_line(f'{name} = {number},')
+
+            style_name = 'k' + ProtoMessageField.upper_camel_case(
+                name[len(common_prefix):])
+            if style_name != name:
+                output.write_line(f'{style_name} = {name},')
+
     output.write_line('};')