Kong tag PR fixes (#12)

* Removed bubbling errors in favour of panic
* Added a test for Parse with a bad build and an arg.
* Removed is() function in favour of a switch with strings
* Collect key and value in parseCSV, reducing complexity.
* Fix in global to not use parser instance on error.

tag.go

@@ -1,7 +1,6 @@
 package kong
 
 import (
-	"fmt"
 	"reflect"
 	"strings"
 	"unicode/utf8"
@@ -21,19 +20,21 @@ type Tag struct {
 	Short       rune
 }
 
-func parseCSV(s string) ([]string, error) {
-	num := 0
-	parts := []string{}
-	current := []rune{}
+func parseCSV(s string) map[string]string {
+	d := map[string]string{}
+
+	key := []rune{}
+	value := []rune{}
+	quotes := false
+	inKey := true
 
 	add := func() {
-		parts = append(parts, string(current))
-		current = []rune{}
-		num++
+		d[string(key)] = string(value)
+		key = []rune{}
+		value = []rune{}
+		inKey = true
 	}
 
-	quotes := false
-
 	runes := []rune(s)
 	for idx := 0; idx < len(runes); idx++ {
 		r := runes[idx]
@@ -48,6 +49,10 @@ func parseCSV(s string) ([]string, error) {
 			add()
 			continue
 		}
+		if r == '=' && inKey {
+			inKey = false
+			continue
+		}
 		if r == '\\' {
 			if next == '\'' {
 				idx++
@@ -59,72 +64,60 @@ func parseCSV(s string) ([]string, error) {
 				if next == ',' || eof {
 					continue
 				}
-				return parts, fmt.Errorf("%v has an unexpected char at pos %v", s, idx)
+				fail("%v has an unexpected char at pos %v", s, idx)
 			} else {
 				quotes = true
 				continue
 			}
 		}
-		current = append(current, r)
+		if inKey {
+			key = append(key, r)
+		} else {
+			value = append(value, r)
+		}
 	}
 	if quotes {
-		return parts, fmt.Errorf("%v is not quoted properly", s)
+		fail("%v is not quoted properly", s)
 	}
 
 	add()
 
-	return parts, nil
+	return d
 }
 
-func parseTag(fv reflect.Value, s string) (*Tag, error) {
+func parseTag(fv reflect.Value, s string) *Tag {
 	t := &Tag{}
 	if s == "" {
-		return t, nil
+		return t
 	}
 
-	parts, err := parseCSV(s)
-	if err != nil {
-		return t, err
-	}
-
-	for _, part := range parts {
-		is := func(m string) bool { return part == m }
-		value := func(m string) (string, bool) {
-			split := strings.SplitN(part, "=", 2)
-			if split[0] != m {
-				return "", false
-			}
-			if len(split) == 1 {
-				return "", true
-			}
-			return split[1], true
-		}
-
-		if is("cmd") {
+	for k, v := range parseCSV(s) {
+		switch k {
+		case "cmd":
 			t.Cmd = true
-		} else if is("arg") {
+		case "arg":
 			t.Arg = true
-		} else if is("required") {
+		case "required":
 			t.Required = true
-		} else if is("optional") {
+		case "optional":
 			t.Optional = true
-		} else if v, ok := value("default"); ok {
+		case "default":
 			t.Default = v
-		} else if v, ok := value("help"); ok {
+		case "help":
 			t.Help = v
-		} else if v, ok := value("type"); ok {
+		case "type":
 			t.Type = v
-		} else if v, ok := value("placeholder"); ok {
+		case "placeholder":
 			t.Placeholder = v
-		} else if v, ok := value("env"); ok {
+		case "env":
 			t.Env = v
-		} else if v, ok := value("rune"); ok {
+		case "rune":
 			t.Short, _ = utf8.DecodeRuneInString(v)
 			if t.Short == utf8.RuneError {
 				t.Short = 0
 			}
-		} else {
-			return t, fmt.Errorf("%v is an unknown kong key", part)
+		default:
+			fail("%v is an unknown kong key", k)
 		}
 	}
 
@@ -132,5 +125,5 @@ func parseTag(fv reflect.Value, s string) (*Tag, error) {
 		t.Placeholder = strings.ToUpper(dashedString(fv.Type().Name()))
 	}
 
-	return t, nil
+	return t
 }