v0.4.0

This release supports compile-time rewriting of source files via toolexec.
Build your package or binary with go build -toolexec errtrace and all packages
that import errtrace will be automatically instrumented with errtrace.

Added

• Add UnwrapFrame function to extract a single frame from an error.
  You can use this to implement your own trace formatting logic.

• Support extracting trace frames from custom errors.
  Any error value that implements TracePC() uintptr will now
  contribute to the trace.

• Add GetCaller function for error helpers to annotate wrapped errors with
  their caller information instead of the helper. Example:

  //go:noinline
  func Wrapf(err error, msg string, args ...any) {
    caller := errtrace.GetCaller()
    err := ...
    return caller.Wrap(err)
  }

• Implement slog.LogValuer so errors logged with log/slog log the full trace.

• cmd/errtrace:
  Add -no-wrapn option to disable wrapping with generic WrapN functions.
  This is only useful for toolexec mode due to tooling limitations.

• cmd/errtrace:
  Experimental support for instrumenting code with errtrace automatically
  as part of the Go build process.
  Try this out with go build -toolexec=errtrace pkg/to/build.
  Automatic instrumentation only rewrites packages that import errtrace.
  The flag -required-packages can be used to specify which packages
  are expected to import errtrace if they require rewrites.
  Example: go build -toolexec="errtrace -required-packages pkg/..." pkg/to/build

Changed

• Update go directive in go.mod to 1.21, and drop compatibility with Go 1.20 and earlier.
• Errors wrapped with errtrace are now compatible with log/slog-based loggers,
  and will report the full error trace when logged.

Fixed

• cmd/errtrace: Don't exit with a non-zero status when -h is used.
• cmd/errtrace: Don't panic on imbalanced assignments inside defer blocks.