rust: add test where discriminant is offset from beginning in the variant data layoutupstream-main

This is an optimisation which the Rust compiler can make by overlapping
the discriminant with variant members data locations while exploiting
bit patterns which would be illegal for the variant members.

PiperOrigin-RevId: 635414233
Change-Id: I5da9db7326dfea4756b8edebd19fa8e6c30ea30a

2 files changed, 119 insertions, 0 deletions

diff --git a/test_cases/info_tests/variant/expected/offset_discriminant_rs.elf_stg b/test_cases/info_tests/variant/expected/offset_discriminant_rs.elf_stg
new file mode 100644
index 0000000..e7ab069
--- /dev/null
+++ b/test_cases/info_tests/variant/expected/offset_discriminant_rs.elf_stg
@@ -0,0 +1,106 @@
+version: 0x00000002
+root_id: 0x84ea5130  # interface
+primitive {
+  id: 0x384f7d7c
+  name: "char"
+  encoding: UTF
+  bytesize: 0x00000004
+}
+primitive {
+  id: 0x62aebfd4
+  name: "bool"
+  encoding: BOOLEAN
+  bytesize: 0x00000001
+}
+primitive {
+  id: 0xd4bacb77
+  name: "u32"
+  encoding: UNSIGNED_INTEGER
+  bytesize: 0x00000004
+}
+member {
+  id: 0x16e523e2
+  type_id: 0xd4bacb77  # u32
+  offset: 32
+}
+member {
+  id: 0x97813cf0
+  name: "__0"
+  type_id: 0x384f7d7c  # char
+}
+member {
+  id: 0xdbc0cd2f
+  name: "__1"
+  type_id: 0x384f7d7c  # char
+  offset: 32
+}
+variant_member {
+  id: 0x56b9f935
+  name: "Two"
+  type_id: 0x573dc947
+}
+variant_member {
+  id: 0x69cfc441
+  name: "One"
+  discriminant_value: 1114112
+  type_id: 0x988e2459
+}
+variant_member {
+  id: 0x276cfc01
+  name: "Zero"
+  discriminant_value: 1114113
+  type_id: 0xb2cd8432
+}
+struct_union {
+  id: 0x988e2459
+  kind: STRUCT
+  name: "offset_discriminant::Foo::One"
+  definition {
+    bytesize: 8
+    member_id: 0x97813cf0  # char __0
+  }
+}
+struct_union {
+  id: 0x573dc947
+  kind: STRUCT
+  name: "offset_discriminant::Foo::Two"
+  definition {
+    bytesize: 8
+    member_id: 0x97813cf0  # char __0
+    member_id: 0xdbc0cd2f  # char __1
+  }
+}
+struct_union {
+  id: 0xb2cd8432
+  kind: STRUCT
+  name: "offset_discriminant::Foo::Zero"
+  definition {
+    bytesize: 8
+  }
+}
+variant {
+  id: 0x82b2aa29
+  name: "offset_discriminant::Foo"
+  bytesize: 8
+  discriminant: 0x16e523e2
+  member_id: 0x56b9f935
+  member_id: 0x69cfc441
+  member_id: 0x276cfc01
+}
+function {
+  id: 0x9efcc134
+  return_type_id: 0x62aebfd4  # bool
+  parameter_id: 0x82b2aa29  # variant offset_discriminant::Foo
+}
+elf_symbol {
+  id: 0x699cebd9
+  name: "is_zero"
+  is_defined: true
+  symbol_type: FUNCTION
+  type_id: 0x9efcc134  # bool(variant offset_discriminant::Foo)
+  full_name: "offset_discriminant::is_zero"
+}
+interface {
+  id: 0x84ea5130
+  symbol_id: 0x699cebd9  # bool offset_discriminant::is_zero(variant offset_discriminant::Foo)
+}
diff --git a/test_cases/info_tests/variant/offset_discriminant.rs b/test_cases/info_tests/variant/offset_discriminant.rs
new file mode 100644
index 0000000..a7aca13
--- /dev/null
+++ b/test_cases/info_tests/variant/offset_discriminant.rs
@@ -0,0 +1,13 @@
+pub enum Foo {
+    Two(char, char),
+    One(char),
+    Zero,
+}
+
+#[no_mangle]
+pub fn is_zero(foo: Foo) -> bool {
+    match foo {
+        Foo::Zero => true,
+        _ => false,
+    }
+}