panic: comparing uncomparable type propagation.compositeTextMapPropagator

[corani]

Description

Calling otel.SetTextMapPropagator with a propagation.NewCompositeTextMapPropagator panics.

Environment

• OS: Linux
• Architecture: x86
• Go Version: 1.17.8
• opentelemetry-go version: 1.6.2

Steps To Reproduce

package main

import (
    "go.opentelemetry.io/otel"
    "go.opentelemetry.io/otel/propagation"
)

func main() {
    prop := propagation.NewCompositeTextMapPropagator(
        // anything
    )

    otel.SetTextMapPropagator(prop) // this works
    otel.SetTextMapPropagator(prop) // this panics
}

results in:

panic: runtime error: comparing uncomparable type propagation.compositeTextMapPropagator

Expected behavior

This worked in 1.6.1.

Issue was introduced in 1.6.2, in otel/internal/global/state.go:79.

[corani]

Appears to have been introduced in #2749

[dmathieu]

I guess this happens because we moved the comparison outside of delegateTextMapPropagatorOnce.Do.
So re-setting the propagator used not to run the comparison.

[corani]

Confirmed fixed, thanks for the quick action!