[receiver/filelog] Add operator no longer able to pull env vars with the env function

[atoulme]

Component(s)

receiver/filelog

What happened?

See signalfx/splunk-otel-collector-chart#904 for original report.

The commit 44e1f67#diff-1d453bc7c5b0dd32eec0c83b9b06e6aeb291890d5cf7585d437cee1c209e40b4L123 changed the default value of the env function to be os_env_func with the ability to patch back the calls to env to match os_env_func.

The backwards compatibility work is done when parsing the expression with a patcher struct that performs the string change:

type patcher struct{}

func (p *patcher) Visit(node *ast.Node) {
	n, ok := (*node).(*ast.CallNode)
	if !ok {
		return
	}
	c, ok := (n.Callee).(*ast.IdentifierNode)
	if !ok {
		return
	}
	if c.Value == "env" {
		c.Value = "os_env_func"
	}
}

However, this patcher struct is not used consistently across all usages of the expr compilation work. The add operator specifically doesn't use it, and therefore fails to find the environment variable lookup function.

#26374

Collector version

0.83.0

Environment information

Environment

OS: (e.g., "Ubuntu 20.04")
Compiler(if manually compiled): (e.g., "go 14.2")

OpenTelemetry Collector configuration

No response

Log output

No response

Additional context

No response

[github-actions]

Pinging code owners:

• receiver/filelog: @djaglowski

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