Implemented error messages

src/errors/Error.go

@@ -0,0 +1,67 @@
+package errors
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"git.akyoto.dev/cli/q/src/build/token"
+)
+
+// Error is a compiler error at a given line and column.
+type Error struct {
+	Path   string
+	Line   int
+	Column int
+	Err    error
+	Stack  string
+}
+
+// New generates an error message at the current token position.
+// The error message is clickable in popular editors and leads you
+// directly to the faulty file at the given line and position.
+func New(err error, path string, tokens []token.Token, cursor int) *Error {
+	var (
+		lineCount = 1
+		lineStart = -1
+	)
+
+	for i := range cursor {
+		if tokens[i].Kind == token.NewLine {
+			lineCount++
+			lineStart = int(tokens[i].Position)
+		}
+	}
+
+	var column int
+
+	if cursor < len(tokens) {
+		column = tokens[cursor].Position - lineStart
+	} else {
+		lastToken := tokens[len(tokens)-1]
+		column = lastToken.Position - lineStart + len(lastToken.Text())
+	}
+
+	return &Error{path, lineCount, column, err, Stack()}
+}
+
+// Error generates the string representation.
+func (e *Error) Error() string {
+	path := e.Path
+	cwd, err := os.Getwd()
+
+	if err == nil {
+		relativePath, err := filepath.Rel(cwd, e.Path)
+
+		if err == nil {
+			path = relativePath
+		}
+	}
+
+	return fmt.Sprintf("%s:%d:%d: %s\n\n%s", path, e.Line, e.Column, e.Err, e.Stack)
+}
+
+// Unwrap returns the wrapped error.
+func (e *Error) Unwrap() error {
+	return e.Err
+}