Build splatted attributes in a single output buffer

[OskarEichler]

Summary

Build splatted HTML attributes in one output buffer instead of allocating a result string for every attribute and then joining an array. Preserve attribute ordering, quoting and boolean handling.

Measurements

Ruby 4.0.6 with explicit YJIT; three alternating original/fixed pairs, five batches of 30,000 build_attrs calls per case (median over 15 batches):

Case	Original time / allocations	Patched time / allocations
8 sorted attributes (default)	0.067717 s / 660,000	0.053864 s / 390,000
32 sorted attributes	0.245998 s / 2,100,000	0.194801 s / 1,110,000
8 unsorted attributes	0.044375 s / 330,000	0.022923 s / 30,000
32 unsorted attributes	0.149172 s / 1,050,000	0.081655 s / 30,000

The benchmark prepopulates a Builder with string keys and a mix of true/string values, warms it, then measures only repeated build_attrs calls using monotonic time and total_allocated_objects. Empty and single-attribute cases also improved. These are local microbenchmarks, not application throughput claims.

Verification

• Unmodified core/plugin suites: 415 runs / 650 assertions passing on Ruby 3.2.11 and 4.0.6; existing Rails suite 15 runs / 36 assertions passing on each.
• 4,800 focused comparisons per Ruby against the original algorithm, with sorted/unsorted output, XHTML/HTML, both quote styles and scalar/Unicode values; repeated calls preserve state/output.
• Syntax passes; no new comparative Lint offenses. No test files changed.

Compatibility / limitations

No intended output/API break or dependency change. Ordering and quoting options are retained. Performance varies by Ruby/workload; JRuby and the full supported-Ruby matrix have not been benchmarked.