This change
- Removes interface `log.Format`,
- Removes method `log.FormatFunc`,
- unexports `TerminalHandler.TerminalFormat` formatting methods (renamed to `TerminalHandler.format`)
- removes the notion of `log.Lazy` values
The lazy handler was useful in the old log package, since it
could defer the evaluation of costly attributes until later in the
log pipeline: thus, if the logging was done at 'Trace', we could
skip evaluation if logging only was set to 'Info'.
With the move to slog, this way of deferring evaluation is no longer
needed, since slog introduced 'Enabled': the caller can thus do
the evaluate-or-not decision at the callsite, which is much more
straight-forward than dealing with lazy reflect-based evaluation.
Also, lazy evaluation would not work with 'native' slog, as in, these
two statements would be evaluated differently:
```golang
log.Info("foo", "my lazy", lazyObj)
slog.Info("foo", "my lazy", lazyObj)
```
This PR replaces Geth's logger package (a fork of [log15](https://github.com/inconshreveable/log15)) with an implementation using slog, a logging library included as part of the Go standard library as of Go1.21.
Main changes are as follows:
* removes any log handlers that were unused in the Geth codebase.
* Json, logfmt, and terminal formatters are now slog handlers.
* Verbosity level constants are changed to match slog constant values. Internal translation is done to make this opaque to the user and backwards compatible with existing `--verbosity` and `--vmodule` options.
* `--log.backtraceat` and `--log.debug` are removed.
The external-facing API is largely the same as the existing Geth logger. Logger method signatures remain unchanged.
A small semantic difference is that a `Handler` can only be set once per `Logger` and not changed dynamically. This just means that a new logger must be instantiated every time the handler of the root logger is changed.
----
For users of the `go-ethereum/log` module. If you were using this module for your own project, you will need to change the initialization. If you previously did
```golang
log.Root().SetHandler(log.LvlFilterHandler(log.LvlInfo, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
```
You now instead need to do
```golang
log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelInfo, true)))
```
See more about reasoning here: https://github.com/ethereum/go-ethereum/issues/28558#issuecomment-1820606613
* cmd/geth: more testcases for logging
This adds more edgecases around logging, particularly around handling of different types of nil-values
as concrete types and within interfaces.
Also adds tests with 'reserved' values which breaks json/logfmt formats. The json output is checked in,
but not actively used by any testcase at the moment.
* cmd/geth/testdata: remove timestamps
This PR is a bit in preparation for the slog work in #28187 .
Our current test re logging mostly test the internals, but we have no real end-to-end test of the logging output. This PR introduces a simple reexec-based log tester. This also relies upon a special mode in geth, which can be made to eject a set of predefined log messages (only available if the build-tag `integrationtests` is used
e.g. go run --tags=integrationtests ./cmd/geth --log.format terminal logtest
While working on this, I also noticed a quirk in the setup: when geth was configured to use a file output, then two separate handlers were used (one handler for the file, one handler for the console). Using two separate handlers means that two formatters are used, thus the formatting of any/all records happened twice. This PR changes the mechanism to use two separate io.Writers instead, which is both more optimal and fixes a bug which occurs due to a global statefulness in the formatter.
