Parameter field (#16)

https://en.wikipedia.org/wiki/Printf#Parameter_field

src/lib.rs

@@ -119,7 +119,7 @@ use std::path::Path;
 // regex that tries to parse printf's format placeholders
 // see: https://docs.microsoft.com/en-us/cpp/c-runtime-library/format-specification-syntax-printf-and-wprintf-functions?view=msvc-160
 static RE_PRINTF: Lazy<Regex> = Lazy::new(|| {
-    Regex::new(r#"%([-+#])?(\d+)?(\.\d+)?([dis@xXf])|\\u([0-9a-fA-F]{4})|\\.|%%|%$|"|[^%"\\]+"#)
+    Regex::new(r#"%((?P<parameter>\d+)\$)?(?P<flags>[-+#])?(?P<width>\d+)?(?P<precision>\.\d+)?(?P<type>[dis@xXf])|\\u(?P<unicode>[0-9a-fA-F]{4})|\\.|%%|%$|"|[^%"\\]+"#)
         .unwrap()
 });
 static RE_LANG: Lazy<Regex> = Lazy::new(|| Regex::new(r"(\w+)(-(\w+))?").unwrap());
@@ -434,15 +434,23 @@ impl TwineFormatter {
             // transform all printf's format placeholder to Rust's format
             let mut out = String::new();
             for caps in RE_PRINTF.captures_iter(text.as_str()) {
-                if let Some(type_) = caps.get(4) {
-                    out.push_str("{:");
-                    if let Some(flag) = caps.get(1) {
+                if let Some(type_) = caps.name("type") {
+                    out.push_str("{");
+                    if let Some(parameter) = caps.name("parameter") {
+                        let parameter: usize = parameter
+                            .as_str()
+                            .parse()
+                            .expect("could not parse parameter index");
+                        write!(out, "{}", parameter.saturating_sub(1))?;
+                    }
+                    out.push_str(":");
+                    if let Some(flag) = caps.name("flags") {
                         out.push_str(flag.as_str());
                     }
-                    if let Some(width) = caps.get(2) {
+                    if let Some(width) = caps.name("width") {
                         out.push_str(width.as_str());
                     }
-                    if let Some(precision) = caps.get(3) {
+                    if let Some(precision) = caps.name("precision") {
                         out.push_str(precision.as_str());
                     }
                     match type_.as_str() {
@@ -454,7 +462,7 @@ impl TwineFormatter {
                     out.push_str("%");
                 } else if &caps[0] == "\"" {
                     out.push_str("\\\"");
-                } else if let Some(unicode) = caps.get(5) {
+                } else if let Some(unicode) = caps.name("unicode") {
                     out.push_str(r"\u{");
                     out.push_str(unicode.as_str());
                     out.push_str(r"}");

tests/test-crate/src/my_module.rs

@@ -11,6 +11,7 @@ pub fn basic() {
         println!("{}", t!(fallback_to_default_lang => lang));
         println!("{}", t!(name_with_dot_in_it => lang));
         println!("{}", t!(stuff_with_escaped_sequences_and_double_quotes => lang));
+        println!("{}", t!(format_parameter_posix_extension, 1, 2 => lang));
     }
 
     assert_eq!(

tests/test-crate/translations.ini

@@ -32,3 +32,6 @@
     en = Name with a dot
 [stuff_with_escaped_sequences_and_double_quotes]
     en = Stuff with\nescaped\tsequences and "double quotes"
+[format_parameter_posix_extension]
+    en = %1$s %2$4s
+    fr = %2$s %1$4s

tests/ui.rs

@@ -7,6 +7,7 @@ Hello, World !
 Hello
 Name with a dot
 Stuff with\nescaped\tsequences and \"double quotes\"
+2    1
 Ruin a band name by translating it in French
 Rage Against the Machine
 Hello, World!
@@ -15,6 +16,7 @@ badcafe
 Hello
 Name with a dot
 Stuff with\nescaped\tsequences and \"double quotes\"
+1    2
 Ruin a band name by translating it in French
 Wrath Against the Machine
 Hello, World!
@@ -23,6 +25,7 @@ badcafe
 Hello
 Name with a dot
 Stuff with\nescaped\tsequences and \"double quotes\"
+1    2
 ";
 
 #[test]