canon log maybe??

sketch.wat

(component
  (canon log (level info) (num-strings 2) (core func $basic-log))
  (canon log (level warn) (num-strings 2) (format 1 "at {0} I thought {1}") (core func $formatted-warning))
  (core module $M
    (import "" "basic-log" (func $basic-log (param $str1-ptr i32) (param $str1-len i32)
                                            (param $str2-ptr i32) (param $str2-len i32))
    (import "" "formatted-warning" (func $fancy-log (param $str1-ptr i32) (param $str1-len i32)
                                                    (param $str2.1-ptr i32) (param $str2.1-len i32)
                                                    (param $str2.2-ptr i32) (param $str2.2-len i32))            
    ...
  )
  (core instance $m (instantiate $M (with "" (instance
    (export "basic-log" (func $basic-log))
    (export "formatted-warning" (func $formatted-warning))
  ))))
)

• I don't know if it's too general to allow canon log to declare how many strings it outputs, but it nicely avoids the arbitrariness of baking in "2".
• The reason for having a formatting string as a string immediate of canon log (instead of having the wasm code do it itself) is that, when logging is turned off or dialed down (only error/warn, not info, etc), you don't have the wasm code wasting cycles formatting strings that are then ignored.
• While it's tempting to consider a canon get-log-level built-in that lets you query the current log level at runtime (and avoid unnecessary formatting if not needed), I think mayyybe a useful property is that enabling/disabling logging has zero semantic effect on the execution which should help avoid Heisenbugs or "crashes when logging enabled". A key part of this is that if you pass garbage i32 pointers/lengths to canon log it's specified never to trap (just maybe produce garbled output or some "" message).