Add filename, line number and column number to error context (#67)

* feat: add filename, line number and column number to scanner context

* feat: limit the output error context and add filename to wbnf test command error

ast/helpers.go

@@ -1,6 +1,8 @@
 package ast
 
-import "github.com/arr-ai/wbnf/parser"
+import (
+	"github.com/arr-ai/wbnf/parser"
+)
 
 // Which returns the first child of the branch from the list of names supplied
 func Which(b Branch, names ...string) (string, Children) {

cmd/test.go

@@ -141,7 +141,7 @@ func test(c *cli.Context) error {
 	if !g.HasRule(parser.Rule(startingRule)) {
 		return fmt.Errorf("starting rule '%s' not in test grammar", startingRule)
 	}
-	tree, err := g.Parse(parser.Rule(startingRule), parser.NewScanner(input))
+	tree, err := g.Parse(parser.Rule(startingRule), parser.NewScannerWithFilename(input, source))
 	if err != nil {
 		if uci, ok := err.(parser.UnconsumedInputError); ok {
 			logrus.Warningln("Partial result:")

parser/error.go

@@ -69,7 +69,7 @@ func UnconsumedInput(residue Scanner, result TreeElement) UnconsumedInputError {
 }
 
 func (e UnconsumedInputError) Error() string {
-	return fmt.Sprintf("unconsumed input: %v", e.residue)
+	return fmt.Sprintf("unconsumed input\n %v", e.residue.Context(DefaultLimit))
 }
 
 func (e UnconsumedInputError) Result() TreeElement { return e.tree }

parser/parser.go

@@ -186,7 +186,7 @@ func getErrorStrings(input *Scanner) string {
 		text = text[:40] + "  ..."
 	}
 
-	return NewScanner(text).Context()
+	return NewScanner(text).Context(DefaultLimit)
 }
 
 func eatRegexp(input *Scanner, re *regexp.Regexp, output *TreeElement) bool {
@@ -233,7 +233,7 @@ func (p *sParser) Parse(scope Scope, input *Scanner, output *TreeElement) error
 	}
 	if ok := eatRegexp(input, p.re, output); !ok {
 		return newParseError(p.rule, "", scope.GetCutPoint(),
-			fmt.Errorf("expect: %s", NewScanner(p.t.String()).Context()),
+			fmt.Errorf("expect: %s", NewScanner(p.t.String()).Context(DefaultLimit)),
 			fmt.Errorf("actual: %s", getErrorStrings(input)), scope.GetCallStack())
 	}
 	return nil
@@ -261,7 +261,7 @@ func (p *reParser) Parse(scope Scope, input *Scanner, output *TreeElement) error
 	}
 	if ok := eatRegexp(input, p.re, output); !ok {
 		return newParseError(p.rule, "", scope.GetCutPoint(),
-			fmt.Errorf("expect: %s", NewScanner(p.re.String()).Context()),
+			fmt.Errorf("expect: %s", NewScanner(p.re.String()).Context(DefaultLimit)),
 			fmt.Errorf("actual: %s", getErrorStrings(input)), scope.GetCallStack())
 	}
 	return nil

parser/scanner.go

@@ -32,6 +32,9 @@ func NewScannerWithFilename(str, filename string) *Scanner {
 }
 
 func NewScannerAt(str string, offset, size int) *Scanner {
+	if offset+size > len(str) {
+		panic(fmt.Errorf("%d is out of range [:%d]", offset+size, len(str)))
+	}
 	return &Scanner{stringSource{origin: &str}, offset, size}
 }
 
@@ -57,12 +60,35 @@ func (s Scanner) Format(state fmt.State, c rune) {
 	}
 }
 
-func (s Scanner) Context() string {
+var (
+	NoLimit      = -1
+	DefaultLimit = 3
+)
+
+func (s Scanner) Context(limitLines int) string {
 	end := s.sliceStart + s.sliceLength
-	return fmt.Sprintf("%s\033[1;31m%s\033[0m%s",
-		s.src.slice(0, s.sliceStart),
+	lineno, colno := s.Position()
+
+	aboveCxt := s.src.slice(0, s.sliceStart)
+	belowCxt := s.src.slice(end, s.src.length()-end)
+	if limitLines != NoLimit {
+		a := strings.Split(aboveCxt, "\n")
+		if len(a) > limitLines {
+			aboveCxt = strings.Join(a[len(a)-limitLines-1:], "\n")
+		}
+		b := strings.Split(belowCxt, "\n")
+		if len(b) > limitLines {
+			belowCxt = strings.Join(b[:limitLines], "\n")
+		}
+	}
+
+	return fmt.Sprintf("\n%s:%d:%d:\n\n%s\033[1;31m%s\033[0m%s",
+		s.Filename(),
+		lineno,
+		colno,
+		aboveCxt,
 		s.slice(),
-		s.src.slice(end, s.src.length()-end),
+		belowCxt,
 	)
 }
 
@@ -89,6 +115,7 @@ func (s Scanner) Skip(i int) *Scanner {
 	return &Scanner{s.src, s.sliceStart + i, s.sliceLength - i}
 }
 
+// Eat returns a scanner containing the next i bytes and advances s past them.
 func (s *Scanner) Eat(i int, eaten *Scanner) *Scanner {
 	eaten.src = s.src
 	eaten.sliceStart = s.sliceStart
@@ -125,7 +152,9 @@ func (s *Scanner) EatRegexp(re *regexp.Regexp, match *Scanner, captures []Scanne
 		for i := range captures {
 			captures[i] = *s.Slice(loc[2*i], loc[2*i+1])
 		}
+
 		*s = *s.Skip(skip)
+
 		return n, true
 	}
 	return 0, false

parser/scanner_test.go

@@ -1,8 +1,9 @@
 package parser
 
 import (
-	"github.com/stretchr/testify/assert"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestScannerLineColumn(t *testing.T) {

wbnf/cutpoints.go

@@ -2,6 +2,7 @@ package wbnf
 
 import (
 	"fmt"
+
 	"github.com/arr-ai/frozen"
 	"github.com/arr-ai/wbnf/parser"
 )

wbnf/grammar_test.go

@@ -49,7 +49,7 @@ func assertParseToNode(t *testing.T, expected parser.Node, rule parser.Rule, inp
 	if assert.NoError(t, err) {
 		return parser.AssertEqualNodes(t, expected, v.(parser.Node))
 	} else {
-		t.Logf("input: %s", input.Context())
+		t.Logf("input: %s", input.Context(parser.NoLimit))
 	}
 	return false
 }
@@ -175,8 +175,8 @@ func TestExprGrammarGrammar(t *testing.T) {
 	parsers := Core()
 	r := parser.NewScanner(exprGrammarSrc)
 	v, err := parsers.Parse("grammar", r)
-	require.NoError(t, err, "r=%v\nv=%v", r.Context(), v)
-	require.Equal(t, len(exprGrammarSrc), r.Offset(), "r=%v\nv=%v", r.Context(), v)
+	require.NoError(t, err, "r=%v\nv=%v", r.Context(parser.NoLimit), v)
+	require.Equal(t, len(exprGrammarSrc), r.Offset(), "r=%v\nv=%v", r.Context(parser.NoLimit), v)
 	assertUnparse(t,
 		`// Simple expression grammar`+
 			`expr->@:[-+]`+