PHP namespaces for nested messages and enums (#4536)

* uses namespaces for nested messages and enums

* fixes namespaces for PHP dist

* fixes namespace for Descriptors, adds Cardinality and Kind

* fixes nested namespaces for reserved words and adds tests

* adds tests and generator fix for php class prefixes

* fixes escaping of protobuf packages, enum comments, misc others

* nice refactor of generated code

* adds class files for backwards compatibility

* simplifies code with templates

* adds compatibility files to makefile

* cleanup of generator and fixes nested namespace bug

* regenerates proto types

* remove internal BC classes

* adds deprecated warning, adds methods back

* simplifies if statement

* fixes dist files

* addresses review comments

* adds back TYPE_URL_PREFIX constant

* adds @deprecated to old nested class files

* skips tests which require a separate process when protobuf.so is enabled

* Adds tests for legacy nested classes that do not require separate processes to test

* uses legacy names for GPBUtil message check

* adds block for IDE @deprecated message

* Namespace for nested message/enum in c extension

* Remove unused code

1 files changed, 110 insertions, 0 deletions

diff --git a/php/src/Google/Protobuf/Internal/FieldDescriptorProto/Type.php b/php/src/Google/Protobuf/Internal/FieldDescriptorProto/Type.php
new file mode 100644
index 00000000..ea228a77
--- /dev/null
+++ b/php/src/Google/Protobuf/Internal/FieldDescriptorProto/Type.php
@@ -0,0 +1,110 @@
+<?php
+# Generated by the protocol buffer compiler.  DO NOT EDIT!
+# source: google/protobuf/descriptor.proto
+
+namespace Google\Protobuf\Internal\FieldDescriptorProto;
+
+/**
+ * Protobuf type <code>google.protobuf.FieldDescriptorProto.Type</code>
+ */
+class Type
+{
+    /**
+     * 0 is reserved for errors.
+     * Order is weird for historical reasons.
+     *
+     * Generated from protobuf enum <code>TYPE_DOUBLE = 1;</code>
+     */
+    const TYPE_DOUBLE = 1;
+    /**
+     * Generated from protobuf enum <code>TYPE_FLOAT = 2;</code>
+     */
+    const TYPE_FLOAT = 2;
+    /**
+     * Not ZigZag encoded.  Negative numbers take 10 bytes.  Use TYPE_SINT64 if
+     * negative values are likely.
+     *
+     * Generated from protobuf enum <code>TYPE_INT64 = 3;</code>
+     */
+    const TYPE_INT64 = 3;
+    /**
+     * Generated from protobuf enum <code>TYPE_UINT64 = 4;</code>
+     */
+    const TYPE_UINT64 = 4;
+    /**
+     * Not ZigZag encoded.  Negative numbers take 10 bytes.  Use TYPE_SINT32 if
+     * negative values are likely.
+     *
+     * Generated from protobuf enum <code>TYPE_INT32 = 5;</code>
+     */
+    const TYPE_INT32 = 5;
+    /**
+     * Generated from protobuf enum <code>TYPE_FIXED64 = 6;</code>
+     */
+    const TYPE_FIXED64 = 6;
+    /**
+     * Generated from protobuf enum <code>TYPE_FIXED32 = 7;</code>
+     */
+    const TYPE_FIXED32 = 7;
+    /**
+     * Generated from protobuf enum <code>TYPE_BOOL = 8;</code>
+     */
+    const TYPE_BOOL = 8;
+    /**
+     * Generated from protobuf enum <code>TYPE_STRING = 9;</code>
+     */
+    const TYPE_STRING = 9;
+    /**
+     * Tag-delimited aggregate.
+     * Group type is deprecated and not supported in proto3. However, Proto3
+     * implementations should still be able to parse the group wire format and
+     * treat group fields as unknown fields.
+     *
+     * Generated from protobuf enum <code>TYPE_GROUP = 10;</code>
+     */
+    const TYPE_GROUP = 10;
+    /**
+     * Length-delimited aggregate.
+     *
+     * Generated from protobuf enum <code>TYPE_MESSAGE = 11;</code>
+     */
+    const TYPE_MESSAGE = 11;
+    /**
+     * New in version 2.
+     *
+     * Generated from protobuf enum <code>TYPE_BYTES = 12;</code>
+     */
+    const TYPE_BYTES = 12;
+    /**
+     * Generated from protobuf enum <code>TYPE_UINT32 = 13;</code>
+     */
+    const TYPE_UINT32 = 13;
+    /**
+     * Generated from protobuf enum <code>TYPE_ENUM = 14;</code>
+     */
+    const TYPE_ENUM = 14;
+    /**
+     * Generated from protobuf enum <code>TYPE_SFIXED32 = 15;</code>
+     */
+    const TYPE_SFIXED32 = 15;
+    /**
+     * Generated from protobuf enum <code>TYPE_SFIXED64 = 16;</code>
+     */
+    const TYPE_SFIXED64 = 16;
+    /**
+     * Uses ZigZag encoding.
+     *
+     * Generated from protobuf enum <code>TYPE_SINT32 = 17;</code>
+     */
+    const TYPE_SINT32 = 17;
+    /**
+     * Uses ZigZag encoding.
+     *
+     * Generated from protobuf enum <code>TYPE_SINT64 = 18;</code>
+     */
+    const TYPE_SINT64 = 18;
+}
+
+// Adding a class alias for backwards compatibility with the previous class name.
+class_alias(Type::class, \Google\Protobuf\Internal\FieldDescriptorProto_Type::class);
+