Fixed a fundamental bug where ^ would always match.

The engine was always passing a string sliced to the current position,
resulting in ^ always matching. Switched to use
FindRunesMatchStartingAt.

Fixes #242.

go.mod

@@ -10,5 +10,6 @@ require (
 	github.com/mattn/go-colorable v0.0.9
 	github.com/mattn/go-isatty v0.0.4
 	github.com/sergi/go-diff v1.0.0 // indirect
+	github.com/stretchr/testify v1.2.2
 	golang.org/x/sys v0.0.0-20181128092732-4ed8d59d0b35 // indirect
 )

lexers/testdata/ballerina.expected

@@ -7,13 +7,16 @@
   {"type":"Text","value":"\n\n"},
   {"type":"KeywordDeclaration","value":"endpoint"},
   {"type":"Text","value":" "},
-  {"type":"NameLabel","value":"http:"},
+  {"type":"Name","value":"http"},
+  {"type":"Operator","value":":"},
   {"type":"Name","value":"Listener"},
   {"type":"Text","value":" "},
   {"type":"Name","value":"listener"},
   {"type":"Text","value":" "},
   {"type":"Operator","value":"{"},
-  {"type":"NameLabel","value":"\n    port:"},
+  {"type":"Text","value":"\n    "},
+  {"type":"Name","value":"port"},
+  {"type":"Operator","value":":"},
   {"type":"Text","value":" "},
   {"type":"Name","value":"9090"},
   {"type":"Text","value":"\n"},

lexers/testdata/csharp.expected

@@ -1,6 +1,6 @@
 [
   {"type":"Name","value":"DriveInfo"},
-  {"type":"NameAttribute","value":"[]"},
+  {"type":"Punctuation","value":"[]"},
   {"type":"Text","value":" "},
   {"type":"Name","value":"drives"},
   {"type":"Text","value":" "},

lexers/testdata/erlang.actual

@@ -0,0 +1,15 @@
+-module(repl).
+
+-export([run/0]).
+
+run() ->
+    read_eval_process().
+
+read_eval_process() ->
+    Line = io:get_line("> "),
+    Out = process_line(Line),
+    io:format("< ~s~n~n", [Out]),
+    read_eval_process().
+
+process_line(Line) ->
+    string:uppercase(Line).

lexers/testdata/erlang.expected

@@ -0,0 +1,79 @@
+[
+  {"type":"Punctuation","value":"-"},
+  {"type":"NameEntity","value":"module"},
+  {"type":"Punctuation","value":"("},
+  {"type":"Name","value":"repl"},
+  {"type":"Punctuation","value":")."},
+  {"type":"Text","value":"\n\n"},
+  {"type":"Punctuation","value":"-"},
+  {"type":"NameEntity","value":"export"},
+  {"type":"Punctuation","value":"(["},
+  {"type":"Name","value":"run"},
+  {"type":"Operator","value":"/"},
+  {"type":"LiteralNumberInteger","value":"0"},
+  {"type":"Punctuation","value":"])."},
+  {"type":"Text","value":"\n\n"},
+  {"type":"NameFunction","value":"run"},
+  {"type":"Punctuation","value":"()"},
+  {"type":"Text","value":" "},
+  {"type":"Operator","value":"-\u003e"},
+  {"type":"Text","value":"\n    "},
+  {"type":"Name","value":"read_eval_process"},
+  {"type":"Punctuation","value":"()."},
+  {"type":"Text","value":"\n\n"},
+  {"type":"NameFunction","value":"read_eval_process"},
+  {"type":"Punctuation","value":"()"},
+  {"type":"Text","value":" "},
+  {"type":"Operator","value":"-\u003e"},
+  {"type":"Text","value":"\n    "},
+  {"type":"NameVariable","value":"Line"},
+  {"type":"Text","value":" "},
+  {"type":"Operator","value":"="},
+  {"type":"Text","value":" "},
+  {"type":"NameNamespace","value":"io"},
+  {"type":"Punctuation","value":":"},
+  {"type":"NameFunction","value":"get_line"},
+  {"type":"Punctuation","value":"("},
+  {"type":"LiteralString","value":"\"\u003e \""},
+  {"type":"Punctuation","value":"),"},
+  {"type":"Text","value":"\n    "},
+  {"type":"NameVariable","value":"Out"},
+  {"type":"Text","value":" "},
+  {"type":"Operator","value":"="},
+  {"type":"Text","value":" "},
+  {"type":"Name","value":"process_line"},
+  {"type":"Punctuation","value":"("},
+  {"type":"NameVariable","value":"Line"},
+  {"type":"Punctuation","value":"),"},
+  {"type":"Text","value":"\n    "},
+  {"type":"NameNamespace","value":"io"},
+  {"type":"Punctuation","value":":"},
+  {"type":"NameFunction","value":"format"},
+  {"type":"Punctuation","value":"("},
+  {"type":"LiteralString","value":"\"\u003c "},
+  {"type":"LiteralStringInterpol","value":"~s~n~n"},
+  {"type":"LiteralString","value":"\""},
+  {"type":"Punctuation","value":","},
+  {"type":"Text","value":" "},
+  {"type":"Punctuation","value":"["},
+  {"type":"NameVariable","value":"Out"},
+  {"type":"Punctuation","value":"]),"},
+  {"type":"Text","value":"\n    "},
+  {"type":"Name","value":"read_eval_process"},
+  {"type":"Punctuation","value":"()."},
+  {"type":"Text","value":"\n\n"},
+  {"type":"NameFunction","value":"process_line"},
+  {"type":"Punctuation","value":"("},
+  {"type":"NameVariable","value":"Line"},
+  {"type":"Punctuation","value":")"},
+  {"type":"Text","value":" "},
+  {"type":"Operator","value":"-\u003e"},
+  {"type":"Text","value":"\n    "},
+  {"type":"NameNamespace","value":"string"},
+  {"type":"Punctuation","value":":"},
+  {"type":"NameFunction","value":"uppercase"},
+  {"type":"Punctuation","value":"("},
+  {"type":"NameVariable","value":"Line"},
+  {"type":"Punctuation","value":")."},
+  {"type":"Text","value":"\n"}
+]

regexp.go

@@ -276,7 +276,7 @@ func (l *LexerState) Iterator() Token {
 		if !ok {
 			panic("unknown state " + l.State)
 		}
-		ruleIndex, rule, groups := matchRules(l.Text[l.Pos:], selectedRule)
+		ruleIndex, rule, groups := matchRules(l.Text, l.Pos, selectedRule)
 		// No match.
 		if groups == nil {
 			// From Pygments :\
@@ -363,7 +363,12 @@ func (r *RegexLexer) maybeCompile() (err error) {
 	for state, rules := range r.rules {
 		for i, rule := range rules {
 			if rule.Regexp == nil {
-				rule.Regexp, err = regexp2.Compile("^(?"+rule.flags+")(?:"+rule.Pattern+")", 0)
+				pattern := "(?:" + rule.Pattern + ")"
+				if rule.flags != "" {
+					pattern = "(?" + rule.flags + ")" + pattern
+				}
+				pattern = `\G` + pattern
+				rule.Regexp, err = regexp2.Compile(pattern, 0)
 				if err != nil {
 					return fmt.Errorf("failed to compile rule %s.%d: %s", state, i, err)
 				}
@@ -415,10 +420,10 @@ func (r *RegexLexer) Tokenise(options *TokeniseOptions, text string) (Iterator,
 	return state.Iterator, nil
 }
 
-func matchRules(text []rune, rules []*CompiledRule) (int, *CompiledRule, []string) {
+func matchRules(text []rune, pos int, rules []*CompiledRule) (int, *CompiledRule, []string) {
 	for i, rule := range rules {
-		match, err := rule.Regexp.FindRunesMatch(text)
-		if match != nil && err == nil {
+		match, err := rule.Regexp.FindRunesMatchStartingAt(text, pos)
+		if match != nil && err == nil && match.Index == pos {
 			groups := []string{}
 			for _, g := range match.Groups() {
 				groups = append(groups, g.String())

regexp_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	"github.com/alecthomas/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestNewlineAtEndOfFile(t *testing.T) {
@@ -25,3 +26,21 @@ func TestNewlineAtEndOfFile(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, []Token{{Error, "hello"}}, it.Tokens())
 }
+
+func TestMatchingAtStart(t *testing.T) {
+	l := Coalesce(MustNewLexer(&Config{}, Rules{
+		"root": {
+			{`\s+`, Whitespace, nil},
+			{`^-`, Punctuation, Push("directive")},
+			{`->`, Operator, nil},
+		},
+		"directive": {
+			{"module", NameEntity, Pop(1)},
+		},
+	}))
+	it, err := l.Tokenise(nil, `-module ->`)
+	assert.NoError(t, err)
+	require.Equal(t,
+		[]Token{{Punctuation, "-"}, {NameEntity, "module"}, {Whitespace, " "}, {Operator, "->"}},
+		it.Tokens())
+}