fix(leaf): preserve quoted secrets across dotenv round trips

internal/leaf/leaf.go

@@ -76,9 +76,22 @@ func Parse(content string) (map[string]string, error) {
 
 func unquote(s string) string {
 	if len(s) >= 2 {
-		if (s[0] == '"' && s[len(s)-1] == '"') || (s[0] == '\'' && s[len(s)-1] == '\'') {
+		if s[0] == '\'' && s[len(s)-1] == '\'' {
 			return s[1 : len(s)-1]
 		}
+		if s[0] == '"' && s[len(s)-1] == '"' {
+			// Decode only the escapes emitted by quote. Other backslash
+			// sequences (such as literal \n in a path) stay untouched.
+			var value strings.Builder
+			for index := 1; index < len(s)-1; index++ {
+				if s[index] == '\\' && index+1 < len(s)-1 &&
+					(s[index+1] == '\\' || s[index+1] == '"') {
+					index++
+				}
+				value.WriteByte(s[index])
+			}
+			return value.String()
+		}
 	}
 	return s
 }
@@ -129,8 +142,8 @@ func quote(v string) string {
 	if v == "" {
 		return v
 	}
-	if strings.ContainsAny(v, " \t\"'#\n") {
-		return `"` + strings.ReplaceAll(v, `"`, `\"`) + `"`
+	if strings.ContainsAny(v, " \t\"'#\n\\") {
+		return `"` + strings.NewReplacer(`\`, `\\`, `"`, `\"`).Replace(v) + `"`
 	}
 	return v
 }

internal/leaf/leaf_test.go

@@ -101,3 +101,37 @@ func TestSerializeWithIgnored(t *testing.T) {
 		t.Fatalf("round trip lost data: %#v", got)
 	}
 }
+
+func TestSerializeQuotedValuesRoundTrip(t *testing.T) {
+	for _, value := range []string{
+		`a"b`, `say "hello"`, `C:\Users\name`, `ends with \`,
+		`literal \n`, `\"`, `single'quote`, " padded ",
+	} {
+		t.Run(value, func(t *testing.T) {
+			for _, ignored := range []bool{false, true} {
+				values := map[string]string{"SECRET": value}
+				content := Serialize(values)
+				if ignored {
+					content = SerializeWithIgnored(nil, values)
+				}
+				got, err := Parse(content)
+				if err != nil {
+					t.Fatal(err)
+				}
+				if got["SECRET"] != value {
+					t.Errorf("ignored=%v: got %q, want %q", ignored, got["SECRET"], value)
+				}
+			}
+		})
+	}
+}
+
+func TestParseSingleQuotedBackslashes(t *testing.T) {
+	got, err := Parse(`SECRET='literal\" and \\'`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got["SECRET"] != `literal\" and \\` {
+		t.Fatalf("single-quoted value changed: %q", got["SECRET"])
+	}
+}