refactoring: fix scanning double dollar in template string

internal/scanner/scanner.rl

@@ -115,11 +115,12 @@ func (lex *Lexer) Lex() *token.Token {
                 | '"'              -> final
             ),
             double_qoute_nonvarname: (
-                (any - [\\{"\r\n] - varname_first) -> double_qoute
+                (any - [\\${"\r\n] - varname_first) -> double_qoute
-                | "\r" @new_line                   -> double_qoute
+                | "\r" @new_line                    -> double_qoute
-                | "\n" @new_line                   -> double_qoute
+                | "\n" @new_line                    -> double_qoute
-                | "\\"                             -> double_qoute_any
+                | "\\"                              -> double_qoute_any
-                | '"'                              -> final
+                | '$'                               -> double_qoute_nonvarname
+                | '"'                               -> final
             );
 
         main := |*

internal/scanner/scanner_test.go

@@ -1628,3 +1628,45 @@ func TestIgnoreControllCharactersAtStringVarOffset(t *testing.T) {
 	actual = string(tkn.Value)
 	assert.DeepEqual(t, expected, actual)
 }
+
+func TestDoubleDollar(t *testing.T) {
+	src := `<?php "$$a";`
+
+	lexer := NewLexer([]byte(src), "7.4", nil)
+
+	expected := "\""
+	tkn := lexer.Lex()
+	actual := string(tkn.Value)
+	assert.DeepEqual(t, expected, actual)
+
+	expected = "$"
+	tkn = lexer.Lex()
+	actual = string(tkn.Value)
+	assert.DeepEqual(t, expected, actual)
+
+	expected = "$a"
+	tkn = lexer.Lex()
+	actual = string(tkn.Value)
+	assert.DeepEqual(t, expected, actual)
+}
+
+func TestTripleDollar(t *testing.T) {
+	src := `<?php "$$$a";`
+
+	lexer := NewLexer([]byte(src), "7.4", nil)
+
+	expected := "\""
+	tkn := lexer.Lex()
+	actual := string(tkn.Value)
+	assert.DeepEqual(t, expected, actual)
+
+	expected = "$$"
+	tkn = lexer.Lex()
+	actual = string(tkn.Value)
+	assert.DeepEqual(t, expected, actual)
+
+	expected = "$a"
+	tkn = lexer.Lex()
+	actual = string(tkn.Value)
+	assert.DeepEqual(t, expected, actual)
+}