Remove redundant otelhttp allocation

[gaiaz-iusipov]

There is no need to wrap MeasurementOption to a slice

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: dmathieu / name: Damien Mathieu (93c0836)
• ✅ login: gaiaz-iusipov / name: Gaiaz Iusipov (6dfba10)
• ✅ login: MrAlias / name: Tyler Yahn (0c1accd)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.5%. Comparing base (af75717) to head (0c1accd).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5842     +/-   ##
=======================================
- Coverage   64.6%   64.5%   -0.1%     
=======================================
  Files        202     202             
  Lines      12591   12589      -2     
=======================================
- Hits        8134    8132      -2     
  Misses      4221    4221             
  Partials     236     236             

Files	Coverage Δ
instrumentation/net/http/otelhttp/handler.go	91.9% <100.0%> (-0.1%)	⬇️
instrumentation/net/http/otelhttp/transport.go	97.4% <100.0%> (-0.1%)	⬇️

[ash2k]

@gaiaz-iusipov @MrAlias @dmathieu May I ask why the change, approved in #5664, was reverted? Vararg slice was allocated once and used 2/multiple times. Now it is allocated on each Add() call. There is/was even a comment, explaining the "why".

See https://go.dev/ref/spec#Passing_arguments_to_..._parameters

See https://fs.blog/chestertons-fence/

var sink []string

func abc(vals ...string) {
	sink = vals
}

func BenchmarkFuncCall(b *testing.B) {
	b.ReportAllocs()
	b.ResetTimer()
	arg := []string{"a", "b", "c"}
	for i := 0; i < b.N; i++ {
		abc(arg...)
	}
}

gives me

BenchmarkFuncCall-10    	1000000000	         0.9481 ns/op	       0 B/op	       0 allocs/op

var sink []string

func abc(vals ...string) {
	sink = vals
}

func BenchmarkFuncCall(b *testing.B) {
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		abc("a", "b", "c")
	}
}

gives me

BenchmarkFuncCall-10    	42442630	        26.69 ns/op	      48 B/op	       1 allocs/op

Put the fence back, please 😁