fix(goi18n): could not extract constant message id (#202)

Author: ksegun

v2/goi18n/extract_command.go

@@ -258,6 +258,16 @@ func extractStringLiteral(expr ast.Expr) (string, bool) {
 			return "", false
 		}
 		return x + y, true
+	case *ast.Ident:
+		switch z := v.Obj.Decl.(type) {
+		case *ast.ValueSpec:
+			s, ok := extractStringLiteral(z.Values[0])
+			if !ok {
+				return "", false
+			}
+			return s, true
+		}
+		return "", false
 	default:
 		return "", false
 	}

v2/goi18n/extract_command_test.go

@@ -185,6 +185,23 @@ zero = "Zero translation"
 			}
 			`,
 		},
+		{
+			name:     "global declaration",
+			fileName: "file.go",
+			file: `package main
+
+			import "github.com/nicksnyder/go-i18n/v2/i18n"
+
+			const constID = "ConstantID"
+			
+			var m = &i18n.Message{
+				ID: constID,
+				Other: "ID is a constant",
+			}
+			`,
+			activeFile: []byte(`ConstantID = "ID is a constant"
+`),
+		},
 	}
 
 	for _, test := range tests {