Declare the priority of options and environments on exporters

[XSAM]

Problem Statement

Comments on options of exporters didn't specify the situation where both option and env are set. For instance,

opentelemetry-go/exporters/otlp/otlptrace/otlptracehttp/options.go

Lines 80 to 99 in 14441ae

	// WithEndpointURL sets the target endpoint URL (scheme, host, port, path) the
	// Exporter will connect to.
	//
	// If the OTEL_EXPORTER_OTLP_ENDPOINT or OTEL_EXPORTER_OTLP_TRACES_ENDPOINT
	// environment variable is set, and this option is not passed, that variable
	// value will be used. If both are set, OTEL_EXPORTER_OTLP_TRACES_ENDPOINT
	// will take precedence.
	//
	// If both this option and WithEndpoint are used, the last used option will
	// take precedence.
	//
	// If an invalid URL is provided, the default value will be kept.
	//
	// By default, if an environment variable is not set, and this option is not
	// passed, "localhost:4318" will be used.
	//
	// This option has no effect if WithGRPCConn is used.
	func WithEndpointURL(u string) Option {
	return wrappedOption{otlpconfig.WithEndpointURL(u)}
	}

If both are set, OTEL_EXPORTER_OTLP_TRACES_ENDPOINT will take precedence.

This actually says when we apply both OTEL_EXPORTER_OTLP_ENDPOINT and OTEL_EXPORTER_OTLP_TRACES_ENDPOINT at the same time, OTEL_EXPORTER_OTLP_TRACES_ENDPOINT will take precedence.

But this description is confusing, as it is after the sentence "If the OTEL_EXPORTER_OTLP_ENDPOINT or OTEL_EXPORTER_OTLP_TRACES_ENDPOINT environment variable is set, and this option is not passed, that variable value will be used.". Users might figure the env would take precedence when both the option and the env for the same feature are set.

Proposed Solution

• Correct the statement mentioned above to prevent confusion.
• Based on the current implementation, we should state that if users apply both options and envs for the same feature, options will take precedence.
• Complement tests for this situation to secure exporters' behavior if there is none.

Packages to check

• otlptrace
  • Correct the comment for the priority of options and environments on otlptracegrpc #5508
  • Correct the comment for the priority of options and environments on otlptracehttp #5584
• Correct the comment for the priority of options and environments on otlpmetric #5641
• otlplog
  • Correct the comment for the priority of options and environments on otlploghttp #5650