[pigeon] added a tool to help with comparing the output of different versions (#390)

packages/pigeon/diff_tool.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+###############################################################################
+# A tool that helps you check the Pigeon output for a given file across
+# different versions of Pigeon.
+#
+# The comparison will be made between the currently checked out sha and the one
+# provided as an argument.
+#
+# usage: ./diff_tool.sh <sha for commit to test against> <path to pigeon file>
+###############################################################################
+
+xHash=$1
+pigeonPath=$2
+diffTool="diff -ru"
+gitTool="git -c advice.detachedHead=false"
+
+generate_everything() {
+  local inputPath=$1
+  local outputDir=$2
+  pub run pigeon \
+    --input "$inputPath" \
+    --dart_out "$outputDir/dart.dart" \
+    --java_out "$outputDir/java.dart" \
+    --objc_header_out "$outputDir/objc.h" \
+    --objc_source_out "$outputDir/objc.m"
+}
+
+yHash=$(git rev-parse HEAD)
+xDir=$(mktemp -d -t $xHash)
+yDir=$(mktemp -d -t $yHash)
+inputPath=$yDir/input.dart
+cp "$pigeonPath" "$inputPath"
+$gitTool checkout $xHash 1> /dev/null
+generate_everything $inputPath $xDir
+$gitTool checkout $yHash 1> /dev/null
+generate_everything $inputPath $yDir
+$diffTool "$yDir" "$xDir"
+rm -rf "$yDir"
+rm -rf "$xDir"