1.1. Use an explicit configuration🔗

Environment variables are convenient for commands and CI. A library or long-running application can pass the same settings directly:

def runProfiled (config : ProfilerConfig) : IO Unit :=
  profile config "worker" do
    span "work" runWork

The main configuration fields are:

Field	Meaning
`enabled`	record spans and export reports
`tracePath`	Trace Event JSON destination
`summaryPath`	strict summary JSON destination
`eventLimit`	maximum retained span count, or no limit
`processName`	process-track label shown by Perfetto

The environment entry point reads these variables:

Variable	Setting
`LEAN_PROFILE`	enable the session unless set to an empty or false-like value
`LEAN_PROFILE_OUT`	trace path
`LEAN_PROFILE_SUMMARY_OUT`	summary path
`LEAN_PROFILE_MAX_EVENTS`	retained event limit
`LEAN_PROFILE_PROCESS_NAME`	Perfetto process label

Keep explicit paths when saving several runs:

LEAN_PROFILE=1 \
LEAN_PROFILE_OUT=build/traces/baseline.json \
LEAN_PROFILE_SUMMARY_OUT=build/summaries/baseline.json \
LEAN_PROFILE_PROCESS_NAME="baseline worker" \
lake exe your_executable