Merge branch 'lukeshu/panic'

4 files changed, 18 insertions, 17 deletions

diff --git a/decode.go b/decode.go
index 976cc6a..1ff8938 100644
--- a/decode.go
+++ b/decode.go
@@ -209,7 +209,7 @@ func (dec *Decoder) DecodeThenEOF(ptr any) (err error) {
 	}
 	c, s, t, _ := dec.io.ReadRuneType()
 	if t != jsonparse.RuneTypeEOF {
-		panic("should not happen")
+		panic(fmt.Errorf("should not happen: .ReadRuneType returned non-EOF after decode without .Reset being called: %v", t))
 	}
 	if s > 0 {
 		return &DecodeError{
@@ -283,7 +283,7 @@ func (dec *Decoder) unreadRune() {
 	if err := dec.io.UnreadRune(); err != nil {
 		// .UnreadRune() must succeed if the previous call was
 		// .ReadRune(), which it always is for this code.
-		panic("should not happen")
+		panic(fmt.Errorf("should not happen: UnreadRune: %w", err))
 	}
 }
 
@@ -302,7 +302,7 @@ func (dec *Decoder) expectRune(ec rune, et jsonparse.RuneType) *DecodeError {
 		return err
 	}
 	if ac != ec || at != et {
-		panic("should not happen")
+		panic(fmt.Errorf("should not happen: expected %q/%v but got %q/%v", ec, et, ac, at))
 	}
 	return nil
 }
@@ -964,7 +964,7 @@ func (dec *Decoder) decodeAny() (any, *DecodeError) {
 	case jsonparse.RuneTypeNullN:
 		return nil, dec.decodeNull()
 	default:
-		panic("should not happen")
+		panic(fmt.Errorf("should not happen: unexpected runeType at beginning of value: %v", t))
 	}
 }
 
@@ -1061,10 +1061,10 @@ func (dec *Decoder) decodeObject(gTyp reflect.Type, decodeKey, decodeVal func()
 		case jsonparse.RuneTypeObjectEnd:
 			return nil
 		default:
-			panic("should not happen")
+			panic(fmt.Errorf("should not happen: unexpected runeType after k/v pair in object: %v", t))
 		}
 	default:
-		panic("should not happen")
+		panic(fmt.Errorf("should not happen: unexpected runeType after opening '{' of object: %v", t))
 	}
 }
 
@@ -1136,7 +1136,7 @@ func (dec *Decoder) decodeArray(gTyp reflect.Type, decodeMember func() *DecodeEr
 		case jsonparse.RuneTypeArrayEnd:
 			return nil
 		default:
-			panic("should not happen")
+			panic(fmt.Errorf("should not happen: unexpected runeType after array item: %v", t))
 		}
 	}
 }
@@ -1175,7 +1175,7 @@ func (dec *Decoder) decodeString(gTyp reflect.Type, out fastio.RuneWriter) *Deco
 			case 't':
 				_, _ = out.WriteRune('\t')
 			default:
-				panic("should not happen")
+				panic(fmt.Errorf("should not happen: unexpected rune after backslash: %q", c))
 			}
 		case jsonparse.RuneTypeStringEscUA:
 			uhex[0], _ = jsonparse.HexToInt(c)
@@ -1253,7 +1253,7 @@ func (dec *Decoder) decodeString(gTyp reflect.Type, out fastio.RuneWriter) *Deco
 		case jsonparse.RuneTypeStringEnd:
 			return nil
 		default:
-			panic("should not happen")
+			panic(fmt.Errorf("should not happen: unexpected runeType in string: %v", t))
 		}
 	}
 }
diff --git a/encode_string.go b/encode_string.go
index 328b07a..208aef4 100644
--- a/encode_string.go
+++ b/encode_string.go
@@ -5,6 +5,7 @@
 package lowmemjson
 
 import (
+	"fmt"
 	"io"
 	"unicode/utf8"
 
@@ -40,7 +41,7 @@ func writeStringShortEscape(w io.Writer, c rune) (int, error) {
 	case '\t':
 		b = 't'
 	default:
-		panic("should not happen")
+		panic(fmt.Errorf("should not happen: writeStringShortEscape called with invalid rune: %q", c))
 	}
 	buf := [2]byte{'\\', b}
 	return w.Write(buf[:])
diff --git a/internal/jsonparse/parse.go b/internal/jsonparse/parse.go
index 7d97be0..73584d9 100644
--- a/internal/jsonparse/parse.go
+++ b/internal/jsonparse/parse.go
@@ -401,7 +401,7 @@ func (par *Parser) PushReadBarrier() {
 	// Sanity checking.
 	par.init()
 	if len(par.stack) == 0 {
-		panic(errors.New("illegal PushReadBarrier call: empty stack"))
+		panic(errors.New("should not happen: illegal PushReadBarrier call: empty stack"))
 	}
 	curState := par.stack[len(par.stack)-1]
 	switch curState {
@@ -415,7 +415,7 @@ func (par *Parser) PushReadBarrier() {
 		RuneTypeNullN:
 		// OK
 	default:
-		panic(fmt.Errorf("illegal PushReadBarrier call: %q", curState))
+		panic(fmt.Errorf("should not happen: illegal PushReadBarrier call: %q", curState))
 	}
 	// Actually push.
 	par.barriers = append(par.barriers, barrier{
@@ -441,7 +441,7 @@ func (par *Parser) PushReadBarrier() {
 func (par *Parser) PushWriteBarrier() {
 	par.init()
 	if len(par.stack) == 0 {
-		panic(errors.New("illegal PushWriteBarrier call: empty stack"))
+		panic(errors.New("should not happen: illegal PushWriteBarrier call: empty stack"))
 	}
 	switch par.stack[len(par.stack)-1] {
 	case runeTypeAny:
@@ -459,14 +459,14 @@ func (par *Parser) PushWriteBarrier() {
 		})
 		par.stack = []RuneType{runeTypeAny}
 	default:
-		panic(fmt.Errorf("illegal PushWriteBarrier call: %q", par.stack[len(par.stack)-1]))
+		panic(fmt.Errorf("should not happen: illegal PushWriteBarrier call: %q", par.stack[len(par.stack)-1]))
 	}
 }
 
 // PopBarrier reverses a call to PushReadBarrier or PushWriteBarrier.
 func (par *Parser) PopBarrier() {
 	if len(par.barriers) == 0 {
-		panic(errors.New("illegal PopBarrier call: empty barrier stack"))
+		panic(errors.New("should not happen: illegal PopBarrier call: empty barrier stack"))
 	}
 	barrier := par.barriers[len(par.barriers)-1]
 	par.barriers = par.barriers[:len(par.barriers)-1]
@@ -828,7 +828,7 @@ func (par *Parser) HandleRune(c rune) (RuneType, error) {
 	case RuneTypeNullL1:
 		return par.expectRune(c, 'l', RuneTypeNullL2, "null", true)
 	default:
-		panic(fmt.Errorf(`invalid stack: "%s"`, par.stackString()))
+		panic(fmt.Errorf(`should not happen: invalid stack: "%s"`, par.stackString()))
 	}
 }
 
diff --git a/reencode.go b/reencode.go
index 232d91d..e48c58c 100644
--- a/reencode.go
+++ b/reencode.go
@@ -519,7 +519,7 @@ func (enc *ReEncoder) handleRuneMain(c rune, t jsonparse.RuneType) error {
 		case 't':
 			err = enc.emit(writeStringChar(enc.out, '\t', BackslashEscapeShort, enc.BackslashEscape))
 		default:
-			panic("should not happen")
+			panic(fmt.Errorf("should not happen: rune %q is not a RuneTypeStringEsc1", c))
 		}
 	case jsonparse.RuneTypeStringEscUA:
 		enc.uhex[0], _ = jsonparse.HexToInt(c)