From 0482b457dff2dc0f809892e49aa6f73b5d348a0e Mon Sep 17 00:00:00 2001
From: Martin Tournoij <martin@arp242.net>
Date: Sun, 26 May 2024 20:03:59 +0100
Subject: [PATCH] Ensure ParseError.Message is always set

ParseError.Error() did:

	msg := pe.Message
	if msg == "" {
		msg = pe.err.Error()
	}

That was fine, but not very useful for people wanting to access the
Message field themselves, especially since err isn't exported.

For example staticcheck does this to add in the filename, and the error
is lost, because Message is often blank:

	% staticcheck
	staticcheck.conf:5:0:  (last key parsed: "dot_import_whitelist") (compile)

We now only use the err field to determine which error usage to display
in ErrorWithUsage()
---
 decode.go |  3 ++-
 error.go  | 25 +++++++------------------
 parse.go  |  4 +++-
 3 files changed, 12 insertions(+), 20 deletions(-)

diff --git a/decode.go b/decode.go
index ff9609c..c05a0b7 100644
--- a/decode.go
+++ b/decode.go
@@ -542,10 +542,11 @@ func (md *MetaData) parseErr(err error) error {
 	k := md.context.String()
 	d := string(md.data)
 	return ParseError{
+		Message:  err.Error(),
+		err:      err,
 		LastKey:  k,
 		Position: md.keyInfo[k].pos.withCol(d),
 		Line:     md.keyInfo[k].pos.Line,
-		err:      err,
 		input:    d,
 	}
 }
diff --git a/error.go b/error.go
index 93a870c..1dd5232 100644
--- a/error.go
+++ b/error.go
@@ -92,16 +92,11 @@ func (p Position) withCol(tomlFile string) Position {
 }
 
 func (pe ParseError) Error() string {
-	msg := pe.Message
-	if msg == "" { // Error from errorf()
-		msg = pe.err.Error()
-	}
-
 	if pe.LastKey == "" {
-		return fmt.Sprintf("toml: line %d: %s", pe.Position.Line, msg)
+		return fmt.Sprintf("toml: line %d: %s", pe.Position.Line, pe.Message)
 	}
 	return fmt.Sprintf("toml: line %d (last key %q): %s",
-		pe.Position.Line, pe.LastKey, msg)
+		pe.Position.Line, pe.LastKey, pe.Message)
 }
 
 // ErrorWithPosition returns the error with detailed location context.
@@ -112,25 +107,19 @@ func (pe ParseError) ErrorWithPosition() string {
 		return pe.Error()
 	}
 
+	// TODO: don't show control characters as literals? This may not show up
+	// well everywhere.
+
 	var (
 		lines = strings.Split(pe.input, "\n")
 		b     = new(strings.Builder)
 	)
-
-	msg := pe.Message
-	if msg == "" {
-		msg = pe.err.Error()
-	}
-
-	// TODO: don't show control characters as literals? This may not show up
-	// well everywhere.
-
 	if pe.Position.Len == 1 {
 		fmt.Fprintf(b, "toml: error: %s\n\nAt line %d, column %d:\n\n",
-			msg, pe.Position.Line, pe.Position.Col)
+			pe.Message, pe.Position.Line, pe.Position.Col)
 	} else {
 		fmt.Fprintf(b, "toml: error: %s\n\nAt line %d, column %d-%d:\n\n",
-			msg, pe.Position.Line, pe.Position.Col, pe.Position.Col+pe.Position.Len-1)
+			pe.Message, pe.Position.Line, pe.Position.Col, pe.Position.Col+pe.Position.Len-1)
 	}
 	if pe.Position.Line > 2 {
 		fmt.Fprintf(b, "% 7d | %s\n", pe.Position.Line-2, expandTab(lines[pe.Position.Line-3]))
diff --git a/parse.go b/parse.go
index 33fb0a8..3f2c090 100644
--- a/parse.go
+++ b/parse.go
@@ -92,6 +92,7 @@ func parse(data string) (p *parser, err error) {
 
 func (p *parser) panicErr(it item, err error) {
 	panic(ParseError{
+		Message:  err.Error(),
 		err:      err,
 		Position: it.pos.withCol(p.lx.input),
 		Line:     it.pos.Len,
@@ -123,10 +124,11 @@ func (p *parser) next() item {
 	if it.typ == itemError {
 		if it.err != nil {
 			panic(ParseError{
+				Message:  it.err.Error(),
+				err:      it.err,
 				Position: it.pos.withCol(p.lx.input),
 				Line:     it.pos.Line,
 				LastKey:  p.current(),
-				err:      it.err,
 			})
 		}