Add the hack_collections compiler option.

Summary:
# What?
Add the `hack_collections` compiler option.

# Why?
`hack_collections`, which was the implicit default in the absence of `arrays` and `no_use_hack_collections`, is now explicit.

# Fixtures
- Add `hack_collections` to `cmd` files.
- Generated fixtures must not change.

# Context
`arraysets`, `no_use_hack_collections`, `stricttypes`, `array_migration`, `shape_arraykeys`, `const_collections` are all compiler options that control the generation of container fields. To make code generator simpler and easier to reason about, identify which of these can be removed/merged.

The new options based on the ones that are currently in use:

`legacy_arrays` replaces `no_use_hack_collections`.
`hack_collections`, which was the implicit default in the absence of `arrays` and `no_use_hack_collections`, is now explicit.
`arrays` will eventually become the default and cease to exist as an explicit option.

# The steps
The item in bold corresponds to the current diff.
1. Use new compiler options based on the ones that already exist.
1. Make arrays the default option.
1. Use the legacy arrays + hack collections logical equivalent of arrays.
1. Introduce hack collections wherever necessary.
1. Replace no use hack collections with legacy arrays.
1. Remove arraysets if arrays present.
1. Rename `no_use_hack_collections` compiler option to `legacy_arrays`.
1. **Add `hack_collections` compiler option.**
1. Remove references to the `arrays` compiler option.
1. Delete the `arrays` compiler option.

Reviewed By: rmakheja

Differential Revision: D67617729

fbshipit-source-id: 5101fc8c1ad54cf168ab70e5e5589922dc71c74c

Author: Satish Kumar

third-party/thrift/src/thrift/compiler/generate/t_hack_generator.cc

@@ -126,9 +126,7 @@ class t_hack_generator : public t_concat_generator {
     array_migration_ = option_is_specified(options, "array_migration");
     arrays_ = option_is_specified(options, "arrays");
     legacy_arrays_ = option_is_specified(options, "legacy_arrays");
-    // Set the future state of compiler options based on the current state.
-    // A subsequent change will remove the current compiler options.
-    hack_collections_ = !arrays_ && !legacy_arrays_;
+    hack_collections_ = option_is_specified(options, "hack_collections");
 
     nullable_everything_ = option_is_specified(options, "nullable_everything");
     const_collections_ = option_is_specified(options, "const_collections");
@@ -7622,6 +7620,7 @@ THRIFT_REGISTER_GENERATOR(
     "    stricttypes      Use Collection classes everywhere rather than "
     "KeyedContainer.\n"
     "    arraysets        Use legacy arrays for sets rather than objects.\n"
+    "                     Either legacy_arrays or hack_collections must be present.\n"
     "    nonullables      Instantiate struct fields within structs, rather "
     "than nullable\n"
     "    structtrait      Add 'use [StructName]Trait;' to generated classes\n"
@@ -7635,6 +7634,7 @@ THRIFT_REGISTER_GENERATOR(
     "    frommap_construct Generate fromMap_DEPRECATED method.\n"
     "    arrays           Use Hack arrays for maps/lists/sets instead of "
     "objects.\n"
+    "    hack_collections Generate hack collections instead of hack arrays.\n"
     "    const_collections Use ConstCollection objects rather than their "
     "mutable counterparts.\n"
     "    typedef          Generate type aliases for all the types defined\n"

third-party/thrift/src/thrift/compiler/test/fixtures/adapter/cmd

@@ -1,5 +1,5 @@
 android: android src/module.thrift
-hack: hack:json,typedef,shapes=1,shapes_use_pipe_structure=1 src/module.thrift
+hack: hack:json,typedef,shapes=1,shapes_use_pipe_structure=1,hack_collections=1 src/module.thrift
 java_deprecated: java_deprecated src/module.thrift
 json: json src/module.thrift
 cpp2: mstch_cpp2:includes=\"adapter_dependency.h\" src/module.thrift

third-party/thrift/src/thrift/compiler/test/fixtures/basic-annotations/cmd

@@ -1,6 +1,6 @@
 android: android src/module.thrift
 java_deprecated: java_deprecated src/module.thrift
-hack: hack:json,server=1,shapes=1,shapes_allow_unknown_fields=1,shapes_use_pipe_structure=1 src/module.thrift
+hack: hack:json,server=1,shapes=1,shapes_allow_unknown_fields=1,shapes_use_pipe_structure=1,hack_collections=1 src/module.thrift
 cpp2: mstch_cpp2 src/module.thrift
 go: mstch_go src/module.thrift
 rust: mstch_rust src/module.thrift

third-party/thrift/src/thrift/compiler/test/fixtures/basic-structured-annotations/cmd

@@ -1,3 +1,3 @@
-hack: hack src/module.thrift
+hack: hack:hack_collections=1 src/module.thrift
 json: json:annotate src/module.thrift
 cpp2: mstch_cpp2 src/module.thrift

third-party/thrift/src/thrift/compiler/test/fixtures/basic/cmd

@@ -1,5 +1,5 @@
 android: android src/module.thrift
-hack: hack:json,server=1,shapes=1,shapes_allow_unknown_fields=1,shapes_use_pipe_structure=1 src/module.thrift
+hack: hack:json,server=1,shapes=1,shapes_allow_unknown_fields=1,shapes_use_pipe_structure=1,hack_collections=1 src/module.thrift
 java_deprecated: java_deprecated src/module.thrift
 json: json src/module.thrift
 json_experimental: json_experimental src/module.thrift

third-party/thrift/src/thrift/compiler/test/fixtures/complex-union/cmd

@@ -1,6 +1,6 @@
 android: android src/module.thrift
 java_deprecated: java_deprecated src/module.thrift
-hack: hack:json=1,protected_unions=1 src/module.thrift
+hack: hack:json=1,protected_unions=1,hack_collections=1 src/module.thrift
 cpp2: mstch_cpp2 src/module.thrift
 go: mstch_go src/module.thrift
 rust: mstch_rust src/module.thrift

third-party/thrift/src/thrift/compiler/test/fixtures/constants/cmd

@@ -1,6 +1,6 @@
 android: android src/module.thrift
 py: py src/module.thrift
-hack: hack:typedef,lazy_constants=1 src/module.thrift
+hack: hack:typedef,lazy_constants=1,hack_collections=1 src/module.thrift
 cpp2: mstch_cpp2 src/module.thrift
 go: mstch_go src/module.thrift
 rust: mstch_rust src/module.thrift

third-party/thrift/src/thrift/compiler/test/fixtures/default_values/cmd

@@ -1,5 +1,5 @@
 cpp2: mstch_cpp2 src/module.thrift
 go: mstch_go src/module.thrift
-hack: hack src/module.thrift
+hack: hack:hack_collections=1 src/module.thrift
 py3: mstch_py3 src/module.thrift
 python: mstch_python src/module.thrift

third-party/thrift/src/thrift/compiler/test/fixtures/doctext/cmd

@@ -1,4 +1,4 @@
 cpp2: mstch_cpp2 src/module.thrift
 go: mstch_go src/module.thrift
 rust: mstch_rust src/module.thrift
-hack: hack src/module.thrift
+hack: hack:hack_collections=1 src/module.thrift

third-party/thrift/src/thrift/compiler/test/fixtures/enums/cmd

@@ -1,5 +1,5 @@
 android: android src/module.thrift
-hack: hack:json,server=1,shapes=1,shapes_allow_unknown_fields=1 src/module.thrift
+hack: hack:json,server=1,shapes=1,shapes_allow_unknown_fields=1,hack_collections=1 src/module.thrift
 json: json src/module.thrift
 java_deprecated: java_deprecated src/module.thrift
 json_experimental: json_experimental src/module.thrift