Rust reflection: simplify dependencies, fix Android build compatibility (#8512)

* flatbuffers Rust reflection: replace num with num-traits

num crate is a wrapper over num-traits and a few other crates, that
reexports the APIs from all of them. We only need num-traits.

Signed-off-by: Marcin Radomski <dextero@google.com>

* Rust reflection: drop dependency on stdint crate

We only use it to get intmax_t for deriving alignment, which is an alias
for `core::ffi::c_long` [1]. We can use that directly instead.

[1] https://docs.rs/stdint/1.0.0/stdint/type.intmax_t.html

Signed-off-by: Marcin Radomski <dextero@google.com>

* Rust reflection: drop dependency on escape_string crate

It's used to format a string used for debugging only, so we might as
well use the builtin Debug representation of a string.

Signed-off-by: Marcin Radomski <dextero@google.com>

* Rust codegen: add derives on generated bitflags

Otherwise it limits the use of structs generated for reflection.fbs
in Rust reflection API.

Signed-off-by: Marcin Radomski <dextero@google.com>

* Rust flatbuffers: update bitflags dependency to 2.8

Signed-off-by: Marcin Radomski <dextero@google.com>

* Rust codegen: use bitflags v2 API for converting from bits

from_bits_unchecked was replaced with safe from_bits_retain.

Signed-off-by: Marcin Radomski <dextero@google.com>

* Regenerate Rust code after idl change

Signed-off-by: Marcin Radomski <dextero@google.com>

* Regenerate reflection_generated.rs

With flatc --rust ../../../reflection/reflection.fbs

Signed-off-by: Marcin Radomski <dextero@google.com>

* ts/BUILD.bazel: add missing import

Found by Buildifire presubmit:

  Function "sh_binary" is not global anymore and needs to be loaded from
  "@rules_shell//shell:sh_binary.bzl".

Signed-off-by: Marcin Radomski <dextero@google.com>

* Update expected value in generated_code_debug_prints_correctly test

In bitflags v2, the debug string representation of enum values is
different than it was in v1:
  Blue -> Color(Blue)
  (empty) -> LongEnum(0x0)

This change adjusts the expected test value.

Signed-off-by: Marcin Radomski <dextero@google.com>

* Fix tests build on Swift 5.8

grpc-swift 1.4.1 depends on swift-nio-ssl 2.14.0+ [1]. swift-nio-ssl 2.29.1
published on 2025-01-30, introduced some code [2] that uses a "switch
expression syntax" supported since Swift 5.9 [3]. Attempts to compile it with
Swift 5.8 cause build errors.

swift-nio-ssl project doesn't seem to support Swift 5.8. A commit from
2024-10-29 removes a "deprecated reference to a Swift 5.8 pipeline" [4].

swift-nio-ssl 2.29.0 is the last version that can be compiled with Swift
5.8. This commit pins it to that exact version.

[1] 66e27d7e84/Package.swift (L33)
[2] 3cb4d5ad12 (diff-bc1db1321ff689c2819245dcce1a3080554f0fc13f81b8d326c97e7d42717c8fR54)
[3] https://github.com/swiftlang/swift-evolution/blob/main/proposals/0380-if-switch-expressions.md
[4] 8a6b89d9a4

---------

Signed-off-by: Marcin Radomski <dextero@google.com>
Co-authored-by: Marcin Radomski <dextero@google.com>

src/idl_gen_rust.cpp

@@ -727,7 +727,7 @@ class RustGenerator : public BaseGenerator {
       code_ += "mod bitflags_{{ENUM_NAMESPACE}} {";
       code_ += "  flatbuffers::bitflags::bitflags! {";
       GenComment(enum_def.doc_comment, "    ");
-      code_ += "    #[derive(Default)]";
+      code_ += "    #[derive(Default, Debug, Clone, Copy, PartialEq)]";
       code_ += "    {{ACCESS_TYPE}} struct {{ENUM_TY}}: {{BASE_TYPE}} {";
       ForAllEnumValues1(enum_def, [&](const EnumVal &ev) {
         this->GenComment(ev.doc_comment, "    ");
@@ -843,20 +843,7 @@ class RustGenerator : public BaseGenerator {
     code_ +=
         "    let b = flatbuffers::read_scalar_at::<{{BASE_TYPE}}>(buf, loc);";
     if (IsBitFlagsEnum(enum_def)) {
-      // Safety:
-      // This is safe because we know bitflags is implemented with a repr
-      // transparent uint of the correct size. from_bits_unchecked will be
-      // replaced by an equivalent but safe from_bits_retain in bitflags 2.0
-      // https://github.com/bitflags/bitflags/issues/262
-      code_ += "    // Safety:";
-      code_ +=
-          "    // This is safe because we know bitflags is implemented with a "
-          "repr transparent uint of the correct size.";
-      code_ +=
-          "    // from_bits_unchecked will be replaced by an equivalent but "
-          "safe from_bits_retain in bitflags 2.0";
-      code_ += "    // https://github.com/bitflags/bitflags/issues/262";
-      code_ += "    Self::from_bits_unchecked(b)";
+      code_ += "    Self::from_bits_retain(b)";
     } else {
       code_ += "    Self(b)";
     }
@@ -884,20 +871,7 @@ class RustGenerator : public BaseGenerator {
     code_ += "  fn from_little_endian(v: {{BASE_TYPE}}) -> Self {";
     code_ += "    let b = {{BASE_TYPE}}::from_le(v);";
     if (IsBitFlagsEnum(enum_def)) {
-      // Safety:
-      // This is safe because we know bitflags is implemented with a repr
-      // transparent uint of the correct size. from_bits_unchecked will be
-      // replaced by an equivalent but safe from_bits_retain in bitflags 2.0
-      // https://github.com/bitflags/bitflags/issues/262
-      code_ += "    // Safety:";
-      code_ +=
-          "    // This is safe because we know bitflags is implemented with a "
-          "repr transparent uint of the correct size.";
-      code_ +=
-          "    // from_bits_unchecked will be replaced by an equivalent but "
-          "safe from_bits_retain in bitflags 2.0";
-      code_ += "    // https://github.com/bitflags/bitflags/issues/262";
-      code_ += "    unsafe { Self::from_bits_unchecked(b) }";
+      code_ += "    Self::from_bits_retain(b)";
     } else {
       code_ += "    Self(b)";
     }