feat: implement slog-based logging

README.md

@@ -46,6 +46,19 @@ go run ./examples/cubic
 
 To design your first circuit, follow the tutorial in [`gnark` User Documentation].
 
+## Logging
+
+`gnark` reads `GNARK_LOG_LEVEL` to configure internal logs:
+
+- `trace`: logs all records and includes source locations.
+- `debug`: logs debug records and startup runtime/build metadata.
+- `info`: logs info records and above. This is the default.
+- `warning` or `warn`: logs warning records and above.
+- `error`: logs error records only.
+- `quiet` or `none`: disables logs.
+
+When built with the `debug` build tag and `GNARK_LOG_LEVEL` is unset, the default level is `debug`.
+
 ## Supported Proving Systems and Curves
 
 `gnark` currently supports:

backend/backend.go

@@ -8,8 +8,10 @@ import (
 	"crypto/sha256"
 	"fmt"
 	"hash"
+	"log/slog"
 
 	"github.com/consensys/gnark/constraint/solver"
+	"github.com/consensys/gnark/internal/logger"
 )
 
 // ID represent a unique ID for a proving scheme
@@ -62,6 +64,7 @@ type ProverConfig struct {
 	ChallengeHash  hash.Hash
 	KZGFoldingHash hash.Hash
 	StatisticalZK  bool
+	Logger         *slog.Logger
 }
 
 // NewProverConfig returns a default ProverConfig with given prover options opts
@@ -72,6 +75,7 @@ func NewProverConfig(opts ...ProverOption) (ProverConfig, error) {
 		// separation tags for PLONK and Groth16
 		ChallengeHash:  sha256.New(),
 		KZGFoldingHash: sha256.New(),
+		Logger:         logger.Logger(),
 	}
 	for _, option := range opts {
 		if err := option(&opt); err != nil {
@@ -81,6 +85,19 @@ func NewProverConfig(opts ...ProverOption) (ProverConfig, error) {
 	return opt, nil
 }
 
+// WithProverLogger sets the logger used by the prover and its internal solver.
+// If this option is not provided, the default logger is used. Passing nil
+// disables logging.
+func WithProverLogger(log *slog.Logger) ProverOption {
+	return func(opt *ProverConfig) error {
+		if log == nil {
+			log = logger.DisabledLogger()
+		}
+		opt.Logger = log
+		return nil
+	}
+}
+
 // WithSolverOptions specifies the constraint system solver options.
 func WithSolverOptions(solverOpts ...solver.Option) ProverOption {
 	return func(opt *ProverConfig) error {
@@ -157,6 +174,8 @@ type VerifierConfig struct {
 	HashToFieldFn  hash.Hash
 	ChallengeHash  hash.Hash
 	KZGFoldingHash hash.Hash
+
+	Logger *slog.Logger
 }
 
 // NewVerifierConfig returns a default [VerifierConfig] with given verifier
@@ -167,6 +186,7 @@ func NewVerifierConfig(opts ...VerifierOption) (VerifierConfig, error) {
 		// separation tags for PLONK and Groth16
 		ChallengeHash:  sha256.New(),
 		KZGFoldingHash: sha256.New(),
+		Logger:         logger.Logger(),
 	}
 	for _, option := range opts {
 		if err := option(&opt); err != nil {
@@ -208,3 +228,15 @@ func WithVerifierKZGFoldingHashFunction(hFunc hash.Hash) VerifierOption {
 		return nil
 	}
 }
+
+// WithVerifierLogger sets the logger used by the verifier. If this option is
+// not provided, the default logger is used. Passing nil disables logging.
+func WithVerifierLogger(log *slog.Logger) VerifierOption {
+	return func(vc *VerifierConfig) error {
+		if log == nil {
+			log = logger.DisabledLogger()
+		}
+		vc.Logger = log
+		return nil
+	}
+}