restore support for escaped quoted char

Signed-off-by: Nicolas De Loof <[email protected]>

dotenv/fixtures/quoted.env

@@ -11,4 +11,5 @@ OPTION_J = 'first line
 second line
 third line
 and so on'
+OPTION_K='Let\'s go!'
 OPTION_Z = "last value"

dotenv/godotenv_test.go

@@ -171,6 +171,7 @@ func TestLoadQuotedEnv(t *testing.T) {
 second line
 third line
 and so on`,
+		"OPTION_K": "Let's go!",
 		"OPTION_Z": "last value",
 	}
 

dotenv/parser.go

@@ -159,27 +159,34 @@ func (p *parser) extractVarValue(src string, envMap map[string]string, lookupFn
 
 	previousCharIsEscape := false
 	// lookup quoted string terminator
+	var chars []byte
 	for i := 1; i < len(src); i++ {
-		if src[i] == '\n' {
+		char := src[i]
+		if char == '\n' {
 			p.line++
 		}
-		if char := src[i]; char != quote {
+		if char != quote {
 			if !previousCharIsEscape && char == '\\' {
 				previousCharIsEscape = true
-			} else {
+				continue
+			}
+			if previousCharIsEscape {
 				previousCharIsEscape = false
+				chars = append(chars, '\\')
 			}
+			chars = append(chars, char)
 			continue
 		}
 
 		// skip escaped quote symbol (\" or \', depends on quote)
 		if previousCharIsEscape {
 			previousCharIsEscape = false
+			chars = append(chars, char)
 			continue
 		}
 
 		// trim quotes
-		value := string(src[1:i])
+		value := string(chars)
 		if quote == prefixDoubleQuote {
 			// expand standard shell escape sequences & then interpolate
 			// variables on the result