feat: lighter stack trace by default for circuits, more verbose when …

…-tags=debug provided

debug/debug.go

@@ -0,0 +1,70 @@
+package debug
+
+import (
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+)
+
+var light = true
+
+func Stack() string {
+	var sbb strings.Builder
+	WriteStack(&sbb)
+	return sbb.String()
+}
+
+func WriteStack(sbb *strings.Builder) {
+	// derived from: https://golang.org/pkg/runtime/#example_Frames
+	// we stop when func name == Define as it is where the gnark circuit code should start
+
+	// Ask runtime.Callers for up to 10 pcs
+	pc := make([]uintptr, 10)
+	n := runtime.Callers(3, pc)
+	if n == 0 {
+		// No pcs available. Stop now.
+		// This can happen if the first argument to runtime.Callers is large.
+		return
+	}
+	pc = pc[:n] // pass only valid pcs to runtime.CallersFrames
+	frames := runtime.CallersFrames(pc)
+	// Loop to get frames.
+	// A fixed number of pcs can expand to an indefinite number of Frames.
+	for {
+		frame, more := frames.Next()
+		fe := strings.Split(frame.Function, "/")
+		function := fe[len(fe)-1]
+		file := frame.File
+
+		if light {
+			if strings.Contains(function, "runtime.gopanic") {
+				continue
+			}
+			if strings.Contains(function, "frontend.(*constraintSystem)") {
+				continue
+			}
+			if strings.Contains(frame.File, "test/engine.go") {
+				continue
+			}
+			if strings.Contains(frame.File, "gnark/frontend") {
+				continue
+			}
+			file = filepath.Base(file)
+		}
+
+		sbb.WriteString(function)
+		sbb.WriteByte('\n')
+		sbb.WriteByte('\t')
+		sbb.WriteString(file)
+		sbb.WriteByte(':')
+		sbb.WriteString(strconv.Itoa(frame.Line))
+		sbb.WriteByte('\n')
+		if !more {
+			break
+		}
+		if strings.HasSuffix(function, "Define") {
+			break
+		}
+	}
+}

debug/debug_full.go

@@ -0,0 +1,8 @@
+//go:build debug
+// +build debug
+
+package debug
+
+func init() {
+	light = false
+}

frontend/cs_api.go

@@ -17,9 +17,7 @@ limitations under the License.
 package frontend
 
 import (
-	"fmt"
 	"math/big"
-	"runtime/debug"
 
 	"github.com/consensys/gnark/backend/hint"
 	"github.com/consensys/gnark/internal/backend/compiled"
@@ -152,8 +150,7 @@ func (cs *constraintSystem) Inverse(i1 interface{}) Variable {
 	if vars[0].isConstant() {
 		c := vars[0].constantValue(cs)
 		if c.IsUint64() && c.Uint64() == 0 {
-			stack := string(debug.Stack())
-			panic(fmt.Sprintf("inverse by constant(0):\n%s", stack))
+			panic("inverse by constant(0)")
 		}
 
 		c.ModInverse(c, cs.curveID.Info().Fr.Modulus())
@@ -189,8 +186,7 @@ func (cs *constraintSystem) Div(i1, i2 interface{}) Variable {
 	// v2 is constant
 	b2 := v2.constantValue(cs)
 	if b2.IsUint64() && b2.Uint64() == 0 {
-		stack := string(debug.Stack())
-		panic(fmt.Sprintf("div by constant(0):\n%s", stack))
+		panic("div by constant(0)")
 	}
 	q := cs.curveID.Info().Fr.Modulus()
 	b2.ModInverse(b2, q)
@@ -221,8 +217,7 @@ func (cs *constraintSystem) DivUnchecked(i1, i2 interface{}) Variable {
 	// v2 is constant
 	b2 := v2.constantValue(cs)
 	if b2.IsUint64() && b2.Uint64() == 0 {
-		stack := string(debug.Stack())
-		panic(fmt.Sprintf("div by constant(0):\n%s", stack))
+		panic("div by constant(0)")
 	}
 	q := cs.curveID.Info().Fr.Modulus()
 	b2.ModInverse(b2, q)

frontend/cs_assertions.go

@@ -19,7 +19,6 @@ package frontend
 import (
 	"fmt"
 	"math/big"
-	"runtime/debug"
 
 	"github.com/consensys/gnark/internal/backend/compiled"
 )
@@ -52,7 +51,7 @@ func (cs *constraintSystem) AssertIsBoolean(i1 interface{}) {
 	if v.isConstant() {
 		c := v.constantValue(cs)
 		if !(c.IsUint64() && (c.Uint64() == 0 || c.Uint64() == 1)) {
-			panic(fmt.Sprintf("assertIsBoolean failed: constant(%s)\n%s", c.String(), string(debug.Stack())))
+			panic(fmt.Sprintf("assertIsBoolean failed: constant(%s)", c.String()))
 		}
 	}
 

frontend/cs_debug.go

@@ -24,6 +24,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/consensys/gnark/debug"
 	"github.com/consensys/gnark/internal/backend/compiled"
 	"github.com/consensys/gnark/internal/parser"
 )
@@ -111,7 +112,7 @@ func printArg(log *compiled.LogEntry, sbb *strings.Builder, a interface{}) {
 }
 
 func (cs *constraintSystem) addDebugInfo(errName string, i ...interface{}) int {
-	var debug compiled.LogEntry
+	var l compiled.LogEntry
 
 	const minLogSize = 500
 	var sbb strings.Builder
@@ -126,7 +127,7 @@ func (cs *constraintSystem) addDebugInfo(errName string, i ...interface{}) int {
 			if len(v.linExp) > 1 {
 				sbb.WriteString("(")
 			}
-			debug.WriteLinearExpression(v.linExp, &sbb)
+			l.WriteLinearExpression(v.linExp, &sbb)
 			if len(v.linExp) > 1 {
 				sbb.WriteString(")")
 			}
@@ -136,15 +137,15 @@ func (cs *constraintSystem) addDebugInfo(errName string, i ...interface{}) int {
 		case int:
 			sbb.WriteString(strconv.Itoa(v))
 		case compiled.Term:
-			debug.WriteTerm(v, &sbb)
+			l.WriteTerm(v, &sbb)
 		default:
 			panic("unsupported log type")
 		}
 	}
 	sbb.WriteByte('\n')
 	debug.WriteStack(&sbb)
-	debug.Format = sbb.String()
+	l.Format = sbb.String()
 
-	cs.debugInfo = append(cs.debugInfo, debug)
+	cs.debugInfo = append(cs.debugInfo, l)
 	return len(cs.debugInfo) - 1
 }

frontend/frontend.go

@@ -22,15 +22,14 @@ import (
 	"fmt"
 	"reflect"
 
+	"github.com/consensys/gnark/debug"
+
 	"github.com/consensys/gnark-crypto/ecc"
 	"github.com/consensys/gnark/backend"
 	"github.com/consensys/gnark/internal/backend/compiled"
 	"github.com/consensys/gnark/internal/parser"
 )
 
-// errInputNotSet triggered when trying to access a variable that was not allocated
-var errInputNotSet = errors.New("variable is not allocated")
-
 // Compile will generate a CompiledConstraintSystem from the given circuit
 //
 // 1. it will first allocate the user inputs (see type Tag for more info)
@@ -91,14 +90,7 @@ func Compile(curveID ecc.ID, zkpID backend.ID, circuit Circuit, opts ...func(opt
 // allocations by parsing the circuit's underlying structure, then
 // it builds the constraint system using the Define method.
 func buildCS(curveID ecc.ID, circuit Circuit, initialCapacity ...int) (cs constraintSystem, err error) {
-	// recover from panics to print user-friendlier messages
-	defer func() {
-		if r := recover(); r != nil {
-			err = fmt.Errorf("%v", r)
-			// TODO @gbotrel with debug buiild tag
-			// fmt.Println(string(debug.Stack()))
-		}
-	}()
+
 	// instantiate our constraint system
 	cs = newConstraintSystem(curveID, initialCapacity...)
 
@@ -133,6 +125,13 @@ func buildCS(curveID ecc.ID, circuit Circuit, initialCapacity ...int) (cs constr
 		return cs, err
 	}
 
+	// recover from panics to print user-friendlier messages
+	defer func() {
+		if r := recover(); r != nil {
+			err = fmt.Errorf("%v\n%s\n", r, debug.Stack())
+		}
+	}()
+
 	// call Define() to fill in the Constraints
 	if err := circuit.Define(curveID, &cs); err != nil {
 		return cs, err

frontend/variable.go

@@ -14,10 +14,13 @@ limitations under the License.
 package frontend
 
 import (
+	"errors"
 	"fmt"
 	"math/big"
 	"strings"
 
+	"github.com/consensys/gnark/debug"
+
 	"github.com/consensys/gnark-crypto/ecc"
 	"github.com/consensys/gnark/internal/backend/compiled"
 
@@ -28,6 +31,9 @@ import (
 	fr_bw6761 "github.com/consensys/gnark-crypto/ecc/bw6-761/fr"
 )
 
+// errNoValue triggered when trying to access a variable that was not allocated
+var errNoValue = errors.New("can't determine API input value")
+
 // Variable of a circuit
 // represents a Variable to a circuit, plus the  linear combination leading to it.
 // the linExp is always non empty, the PartialVariabl can be unset. It is set and allocated in the
@@ -46,16 +52,12 @@ type Variable struct {
 // since a was not in the circuit struct it is not a secret variable
 func (v *Variable) assertIsSet(cs *constraintSystem) {
 	if v.WitnessValue != nil {
-		var l compiled.LogEntry
-		var sbb strings.Builder
-		l.WriteStack(&sbb)
-		panic(fmt.Errorf("variable.WitnessValue is set. this is illegal in Define.\n%s", sbb.String()))
+		// note the compile already checks that, but, if inside a Define, a user mistakingly writes
+		// a.Assign(...) then this will detect it
+		panic("variable.WitnessValue is set. this is illegal in Define")
 	}
 	if len(v.linExp) == 0 {
-		var l compiled.LogEntry
-		var sbb strings.Builder
-		l.WriteStack(&sbb)
-		panic(fmt.Errorf("%w\n%s", errInputNotSet, sbb.String()))
+		panic(errNoValue)
 	}
 
 }
@@ -84,10 +86,9 @@ func (v *Variable) constantValue(cs *constraintSystem) *big.Int {
 // if it is not set this panics
 func (v *Variable) GetWitnessValue(curveID ecc.ID) big.Int {
 	if v.WitnessValue == nil {
-		var l compiled.LogEntry
 		var sbb strings.Builder
-		l.WriteStack(&sbb)
-		panic(fmt.Errorf("%w\n%s", errInputNotSet, sbb.String()))
+		debug.WriteStack(&sbb)
+		panic(fmt.Errorf("%w\n%s", errNoValue, sbb.String()))
 	}
 
 	b := FromInterface(v.WitnessValue)

internal/backend/compiled/log.go

@@ -1,8 +1,6 @@
 package compiled
 
 import (
-	"runtime"
-	"strconv"
 	"strings"
 )
 
@@ -45,44 +43,3 @@ func (l *LogEntry) WriteTerm(t Term, sbb *strings.Builder) {
 
 	l.ToResolve = append(l.ToResolve, t)
 }
-
-func (l *LogEntry) WriteStack(sbb *strings.Builder) {
-	// TODO @gbotrel should be a package level function somewhere (internal), not a method on log.
-	// derived from: https://golang.org/pkg/runtime/#example_Frames
-	// we stop when func name == Define as it is where the gnark circuit code should start
-
-	// Ask runtime.Callers for up to 10 pcs
-	pc := make([]uintptr, 10)
-	n := runtime.Callers(3, pc)
-	if n == 0 {
-		// No pcs available. Stop now.
-		// This can happen if the first argument to runtime.Callers is large.
-		return
-	}
-	pc = pc[:n] // pass only valid pcs to runtime.CallersFrames
-	frames := runtime.CallersFrames(pc)
-	// Loop to get frames.
-	// A fixed number of pcs can expand to an indefinite number of Frames.
-	for {
-		frame, more := frames.Next()
-		fe := strings.Split(frame.Function, "/")
-		function := fe[len(fe)-1]
-		if strings.Contains(function, "frontend.(*ConstraintSystem)") {
-			continue
-		}
-
-		sbb.WriteString(function)
-		sbb.WriteByte('\n')
-		sbb.WriteByte('\t')
-		sbb.WriteString(frame.File)
-		sbb.WriteByte(':')
-		sbb.WriteString(strconv.Itoa(frame.Line))
-		sbb.WriteByte('\n')
-		if !more {
-			break
-		}
-		if strings.HasSuffix(function, "Define") {
-			break
-		}
-	}
-}

test/engine.go

@@ -21,10 +21,11 @@ import (
 	"math/big"
 	"path/filepath"
 	"runtime"
-	"runtime/debug"
 	"strconv"
 	"strings"
 
+	"github.com/consensys/gnark/debug"
+
 	"github.com/consensys/gnark-crypto/ecc"
 	"github.com/consensys/gnark/backend"
 	"github.com/consensys/gnark/backend/hint"
@@ -51,7 +52,6 @@ type engine struct {
 //
 // This is an experimental feature.
 func IsSolved(circuit, witness frontend.Circuit, curveID ecc.ID, opts ...func(opt *backend.ProverOption) error) (err error) {
-
 	// apply options
 	opt, err := backend.NewProverOption(opts...)
 	if err != nil {