From 7e00adcf43b18a22ffbbadc79b8681a5d871f448 Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@lukeshu.com>
Date: Sun, 29 Jan 2023 00:08:22 -0700
Subject: parse: Add a runeTypeAny instead of overloading RuneTypeError

It was confusing.
---
 internal/parse.go | 39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/internal/parse.go b/internal/parse.go
index d917d9d..bb849e7 100644
--- a/internal/parse.go
+++ b/internal/parse.go
@@ -70,6 +70,9 @@ const (
 	RuneTypeNullL2
 
 	RuneTypeEOF
+
+	// Not a real rune type, but used as a stack state.
+	runeTypeAny
 )
 
 // GoString implements fmt.GoStringer.
@@ -127,6 +130,8 @@ func (t RuneType) GoString() string {
 		RuneTypeNullL2: "RuneTypeNullL2",
 
 		RuneTypeEOF: "RuneTypeEOF",
+
+		runeTypeAny: "runeTypeAny",
 	}[t]
 	if ok {
 		return str
@@ -189,6 +194,8 @@ func (t RuneType) String() string {
 		RuneTypeNullL2: "Ⓛ", // +uppercase
 
 		RuneTypeEOF: "$",
+
+		runeTypeAny: "?",
 	}[t]
 	if ok {
 		return str
@@ -234,7 +241,11 @@ type Parser struct {
 	// stack items are "the most recently read stack-relevant
 	// RuneType".
 	//
-	// We treat RuneTypeError as a wildcard.
+	// The stack starts out with the special pseudo-RuneType
+	// `runeTypeAny` that means we're willing to accept any
+	// element type; an empty stack means that we have reached the
+	// end of the top-level element and should accept no more
+	// input except for whitespace.
 	//
 	// The "normal" stack-relevant RuneTypes are:
 	//
@@ -264,12 +275,12 @@ type Parser struct {
 	// The stack would be
 	//
 	//   stack   processed
-	//   x
+	//   ?
 	//   {       {
 	//   »"      {"
 	//   »"      {"x
 	//   »       {"x"
-	//   ox      {"x":
+	//   o?      {"x":
 	//   o"      {"x":"
 	//   o"      {"x":"y
 	//   o       {"x":"y"
@@ -277,7 +288,7 @@ type Parser struct {
 	//   »"      {"x":"y","
 	//   »"      {"x":"y","a
 	//   »       {"x":"y","a"
-	//   ox      {"x":"y","a":
+	//   o?      {"x":"y","a":
 	//   o"      {"x":"y","a":"
 	//   o"      {"x":"y","a":"b
 	//   o       {"x":"y","a":"b"
@@ -308,7 +319,7 @@ func (par *Parser) stackString() string {
 }
 
 func (par *Parser) StackIsEmpty() bool {
-	return len(par.stack) == 0 || (len(par.stack) == 1 && par.stack[0] == RuneTypeError)
+	return len(par.stack) == 0 || (len(par.stack) == 1 && par.stack[0] == runeTypeAny)
 }
 
 // Reset all Parser state.
@@ -342,7 +353,7 @@ func (par *Parser) HandleEOF() (RuneType, error) {
 	}
 	if !par.initialized {
 		par.initialized = true
-		par.pushState(RuneTypeError)
+		par.pushState(runeTypeAny)
 	}
 	switch len(par.stack) {
 	case 0:
@@ -353,7 +364,7 @@ func (par *Parser) HandleEOF() (RuneType, error) {
 			if _, err := par.HandleRune('\n'); err == nil {
 				return RuneTypeEOF, nil
 			}
-		case par.stack[0] == RuneTypeError:
+		case par.stack[0] == runeTypeAny:
 			par.err = io.EOF
 			return RuneTypeError, par.err
 		}
@@ -386,7 +397,7 @@ func (par *Parser) HandleRune(c rune) (RuneType, error) {
 	}
 	if !par.initialized {
 		par.initialized = true
-		par.pushState(RuneTypeError)
+		par.pushState(runeTypeAny)
 	}
 	if len(par.stack) == 0 {
 		switch c {
@@ -398,7 +409,7 @@ func (par *Parser) HandleRune(c rune) (RuneType, error) {
 	}
 	switch par.stack[len(par.stack)-1] {
 	// any /////////////////////////////////////////////////////////////////////////////////////
-	case RuneTypeError:
+	case runeTypeAny:
 		switch c {
 		case 0x0020, 0x000A, 0x000D, 0x0009:
 			return RuneTypeSpace, nil
@@ -449,7 +460,7 @@ func (par *Parser) HandleRune(c rune) (RuneType, error) {
 			return RuneTypeSpace, nil
 		case ':':
 			par.replaceState(RuneTypeObjectComma)
-			par.pushState(RuneTypeError)
+			par.pushState(runeTypeAny)
 			return RuneTypeObjectColon, nil
 		default:
 			return RuneTypeError, fmt.Errorf("invalid character %q after object key", c)
@@ -477,7 +488,7 @@ func (par *Parser) HandleRune(c rune) (RuneType, error) {
 			return RuneTypeArrayEnd, nil
 		default:
 			par.replaceState(RuneTypeArrayComma)
-			par.pushState(RuneTypeError)
+			par.pushState(runeTypeAny)
 			return par.HandleRune(c)
 		}
 	case RuneTypeArrayEnd: // waiting for item
@@ -486,7 +497,7 @@ func (par *Parser) HandleRune(c rune) (RuneType, error) {
 			return RuneTypeSpace, nil
 		default:
 			par.replaceState(RuneTypeArrayComma)
-			par.pushState(RuneTypeError)
+			par.pushState(runeTypeAny)
 			return par.HandleRune(c)
 		}
 	case RuneTypeArrayComma: // waiting for ',' or ']'
@@ -588,8 +599,8 @@ func (par *Parser) HandleRune(c rune) (RuneType, error) {
 	//     H = ExpSign
 	//     I = ExpDig
 	//
-	// The 'A' state is part of the RuneTypeError "any" case
-	// above, and the remainder follow:
+	// The 'A' state is part of the runeTypeAny case above, and
+	// the remainder follow:
 	case RuneTypeNumberIntNeg: // B
 		switch c {
 		case '0':
-- 
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