Change the way PHP7 exception aliasing works

Summary:
fixes #7537
fixes #6747

Old approach: when parsing, replace `Throwable` with `__SystemLib\Throwable`
New approach: when loading the process, actually create `\Throwable` as an alias of `\__SystemLib\Throwable`

get_class() and messages still say systemlib, but this is an improvement.

Reviewed By: mofarrell

Differential Revision: D5031367

fbshipit-source-id: 4985318804c5c5c190cc8141d721e3d3408fb21b

hphp/compiler/parser/parser.cpp

@@ -2529,10 +2529,6 @@ Parser::AliasFlags Parser::getAliasFlags() {
     flags = flags | AliasFlags::PHP7_ScalarTypes;
   }
 
-  if (RuntimeOption::PHP7_EngineExceptions) {
-    flags = flags | AliasFlags::PHP7_EngineExceptions;
-  }
-
   return flags;
 }
 
@@ -2558,8 +2554,6 @@ Parser::AutoAliasMap getAutoAliasedClassesHelper() {
 #define HH_ALIAS(alias, name) \
   ALIAS(#alias, "HH\\" #name, AliasFlags::HH)
 #define SCALAR_TYPE(name) HH_TYPE(name, AliasFlags::PHP7_ScalarTypes)
-#define PHP7_TYPE(name, option) \
-  ALIAS(#name, "__SystemLib\\" #name, AliasFlags::option)
   Parser::AutoAliasMap aliases {
     HH_ONLY_TYPE(AsyncIterator),
     HH_ONLY_TYPE(AsyncKeyedIterator),
@@ -2630,17 +2624,7 @@ Parser::AutoAliasMap getAutoAliasedClassesHelper() {
     HH_ALIAS(integer, int),
     HH_ALIAS(double, float),
     HH_ALIAS(real, float),
-
-    // Engine exception classes
-    PHP7_TYPE(Throwable, PHP7_EngineExceptions),
-    PHP7_TYPE(Error, PHP7_EngineExceptions),
-    PHP7_TYPE(ArithmeticError, PHP7_EngineExceptions),
-    PHP7_TYPE(AssertionError, PHP7_EngineExceptions),
-    PHP7_TYPE(DivisionByZeroError, PHP7_EngineExceptions),
-    PHP7_TYPE(ParseError, PHP7_EngineExceptions),
-    PHP7_TYPE(TypeError, PHP7_EngineExceptions),
   };
-#undef PHP7_TYPE
 #undef HH_ALIAS
 #undef SCALAR_TYPE
 #undef HH_ONLY_TYPE

hphp/compiler/parser/parser.h

@@ -532,7 +532,6 @@ struct Parser : ParserBase {
       None = 0,
       HH = 0x1,
       PHP7_ScalarTypes = 0x2,
-      PHP7_EngineExceptions = 0x4,
     };
 
     struct AutoAlias {

hphp/system/php/lang/Error.php

@@ -0,0 +1,37 @@
+<?php
+class Error implements Throwable {
+  use BaseException;
+  /**
+   * ( excerpt from http://php.net/manual/en/exception.construct.php )
+   *
+   * Constructs the Exception.
+   *
+   * @message    mixed   The Exception message to throw.
+   * @code       mixed   The Exception code.
+   * @previous   mixed   The previous exception used for the exception
+   *                     chaining.
+   */
+  public function __construct($message = '', $code = 0,
+                              \__SystemLib\Throwable $previous = null) {
+
+    // Child classes may just override the protected property
+    // without implementing a constructor or calling parent one.
+    // In this case we should not override it from the param.
+
+    if ($message !== '' || $this->message === '') {
+      $this->message = $message;
+    }
+
+    if ($code !== 0 || $this->code === 0) {
+      $this->code = $code;
+    }
+
+    $this->previous = $previous;
+  }
+}
+
+class ArithmeticError extends Error {}
+class AssertionError extends Error {}
+class DivisionByZeroError extends Error {}
+class ParseError extends Error {}
+class TypeError extends Error {}

hphp/system/php/lang/Throwable.php

@@ -0,0 +1,11 @@
+<?php
+interface Throwable {
+  public function getMessage(): string;
+  public function getCode(): int;
+  public function getFile(): string;
+  public function getLine(): int;
+  public function getTrace(): array;
+  public function getTraceAsString(): string;
+  public function getPrevious(): Throwable;
+  public function __toString(): string;
+}

hphp/system/systemlib.cpp

@@ -16,6 +16,7 @@
 
 #include "hphp/system/systemlib.h"
 #include "hphp/runtime/base/array-init.h"
+#include "hphp/runtime/base/init-fini-node.h"
 #include "hphp/runtime/vm/unit.h"
 #include "hphp/runtime/vm/class.h"
 #include "hphp/runtime/base/execution-context.h"
@@ -250,5 +251,31 @@ void mergePersistentUnits() {
   }
 }
 
+namespace {
+
+#define PHP7_ROOT_ALIAS(x) \
+  auto x##Ne = NamedEntity::get(makeStaticString(#x)); \
+  x##Ne->m_cachedClass.bind(rds::Mode::Persistent); \
+  x##Ne->setCachedClass(SystemLib::s_##x##Class)
+
+InitFiniNode aliasPhp7Classes(
+  []() {
+    if (!RuntimeOption::PHP7_EngineExceptions) {
+      return;
+    }
+    PHP7_ROOT_ALIAS(Throwable);
+    PHP7_ROOT_ALIAS(Error);
+    PHP7_ROOT_ALIAS(ArithmeticError);
+    PHP7_ROOT_ALIAS(AssertionError);
+    PHP7_ROOT_ALIAS(DivisionByZeroError);
+    PHP7_ROOT_ALIAS(ParseError);
+    PHP7_ROOT_ALIAS(TypeError);
+  },
+  InitFiniNode::When::ProcessInit
+);
+
+#undef PHP7_ROOT_ALIAS
+} // namespace
+
 /////////////////////////////////////////////////////////////////////////////
 }} // namespace HPHP::SystemLib

hphp/test/slow/php7_backported/engine-exceptions/throwable_namespace_001.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Foo;
+$y = 'Throwable';
+
+$x = new \Exception();
+var_dump($x instanceof \Throwable);
+var_dump($x instanceof Throwable);
+var_dump($x instanceof $y);

hphp/test/slow/php7_backported/engine-exceptions/throwable_namespace_001.php.expect

@@ -0,0 +1,3 @@
+bool(true)
+bool(false)
+bool(true)

hphp/test/slow/php7_backported/engine-exceptions/throwable_namespace_002.php

@@ -0,0 +1,8 @@
+<?php
+namespace test;
+
+function a(\Throwable $t) {
+  var_dump(get_class($t));
+}
+
+a(new \RuntimeException('foo'));

hphp/test/slow/php7_backported/engine-exceptions/throwable_namespace_002.php.expect

@@ -0,0 +1 @@
+string(16) "RuntimeException"