Enable RuboCop ambiguity rules

[kpumuk]

Enable RuboCop's ambiguity cops for assignments, block association, operators, precedence, ranges, regular expressions, and endless method definitions.

The autocorrections add explicit grouping where Ruby's parse could otherwise be unclear, including mixed arithmetic and bitwise expressions, proc arguments, and RSpec matchers with blocks. These changes preserve behavior while making operator precedence and block ownership visible in the source.

This follows the merged spacing PR #3723; its diff contains only the ambiguity layer.

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[Copilot]

Pull request overview

Enables RuboCop’s ambiguity-related cops for the Ruby codebase (lib/rb) and applies the corresponding autocorrections to make operator precedence and block association explicit (primarily via added parentheses / grouping).

Changes:

• Enabled RuboCop ambiguity cops (assignment, block association, operators/precedence, ranges, regexp literals, endless method definitions).
• Applied autocorrections across Ruby library code, benchmarks, and specs to add explicit grouping for potentially ambiguous expressions.
• Updated a few RSpec expectations to explicitly group matcher arguments to satisfy the new ambiguity cops.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
lib/rb/.rubocop.yml	Enables RuboCop ambiguity cops and endless method ambiguity cop.
lib/rb/spec/socket_spec_shared.rb	Adjusts RSpec expect(...).to ... syntax for block association/ambiguity enforcement.
lib/rb/spec/serializer_spec.rb	Wraps raise_error matcher usage to make block association explicit.
lib/rb/spec/header_transport_spec.rb	Adds grouping around array arithmetic before pack to clarify precedence.
lib/rb/spec/binary_protocol_spec_shared.rb	Adds grouping around exponentiation/arithmetic to clarify precedence in boundary values.
lib/rb/lib/thrift/union.rb	Adds explicit grouping in == to make `
lib/rb/lib/thrift/struct.rb	Adds grouping around arithmetic before bitmask to clarify evaluation order.
lib/rb/lib/thrift/struct_union.rb	Adds explicit grouping around concatenation before appending to map_buf.
lib/rb/lib/thrift/server/nonblocking_server.rb	Makes proc-to-block passing explicit with Thread.new(&shutdown_proc).
lib/rb/lib/thrift/protocol/compact_protocol.rb	Adds grouping around shift/or expressions for clarity and ambiguity-cop compliance.
lib/rb/lib/thrift/protocol/binary_protocol.rb	Adds grouping around exponentiation for max constant definitions.
lib/rb/benchmark/thin_server.rb	Adds grouping around addition before appending to seq.
lib/rb/benchmark/server.rb	Adds grouping around addition before appending to seq.

Suppressed comments (1)

lib/rb/spec/socket_spec_shared.rb:132

• Same issue as above: using .to(receive(...).once { ... }) makes block ownership unclear and is inconsistent with other spec stubbing patterns. Use and_wrap_original to attach the implementation block explicitly.

    expect(IO).to(receive(:select).once { sleep(0.6); nil })

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