4 files changed, 139 insertions, 25 deletions

diff --git a/cmd/vartan/compile.go b/cmd/vartan/compile.go
index 769f143..3601f00 100644
--- a/cmd/vartan/compile.go
+++ b/cmd/vartan/compile.go
@@ -3,8 +3,11 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"io/ioutil"
 	"os"
+	"path/filepath"
 
+	verr "github.com/nihei9/vartan/error"
 	"github.com/nihei9/vartan/grammar"
 	"github.com/nihei9/vartan/spec"
 	"github.com/spf13/cobra"
@@ -28,7 +31,63 @@ func init() {
 }
 
 func runCompile(cmd *cobra.Command, args []string) (retErr error) {
-	gram, err := readGrammar(*compileFlags.grammar)
+	var tmpDirPath string
+	defer func() {
+		if tmpDirPath == "" {
+			return
+		}
+		os.RemoveAll(tmpDirPath)
+	}()
+
+	grmPath := *compileFlags.grammar
+	defer func() {
+		v := recover()
+		if v != nil {
+			err, ok := v.(error)
+			if !ok {
+				retErr = fmt.Errorf("an unexpected error occurred: %v\n", v)
+				fmt.Fprintln(os.Stderr, retErr)
+				return
+			}
+
+			retErr = err
+		}
+
+		if retErr != nil {
+			specErr, ok := retErr.(*verr.SpecError)
+			if ok {
+				if *compileFlags.grammar != "" {
+					specErr.FilePath = grmPath
+					specErr.SourceName = grmPath
+				} else {
+					specErr.FilePath = grmPath
+					specErr.SourceName = "stdin"
+				}
+			}
+			fmt.Fprintln(os.Stderr, retErr)
+		}
+	}()
+
+	if grmPath == "" {
+		var err error
+		tmpDirPath, err = os.MkdirTemp("", "vartan-compile-*")
+		if err != nil {
+			return err
+		}
+
+		src, err := ioutil.ReadAll(os.Stdin)
+		if err != nil {
+			return err
+		}
+
+		grmPath = filepath.Join(tmpDirPath, "stdin.vr")
+		err = ioutil.WriteFile(grmPath, src, 0600)
+		if err != nil {
+			return err
+		}
+	}
+
+	gram, err := readGrammar(grmPath)
 	if err != nil {
 		return err
 	}
@@ -46,17 +105,22 @@ func runCompile(cmd *cobra.Command, args []string) (retErr error) {
 	return nil
 }
 
-func readGrammar(path string) (*grammar.Grammar, error) {
-	r := os.Stdin
-	if path != "" {
-		f, err := os.Open(path)
-		if err != nil {
-			return nil, fmt.Errorf("Cannot open the grammar file %s: %w", path, err)
+func readGrammar(path string) (grm *grammar.Grammar, retErr error) {
+	defer func() {
+		err := recover()
+		specErr, ok := err.(*verr.SpecError)
+		if ok {
+			specErr.FilePath = path
+			retErr = specErr
 		}
-		defer f.Close()
-		r = f
+	}()
+
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("Cannot open the grammar file %s: %w", path, err)
 	}
-	ast, err := spec.Parse(r)
+	defer f.Close()
+	ast, err := spec.Parse(f)
 	if err != nil {
 		return nil, err
 	}
diff --git a/cmd/vartan/parse.go b/cmd/vartan/parse.go
index 8089c5e..ef22ff3 100644
--- a/cmd/vartan/parse.go
+++ b/cmd/vartan/parse.go
@@ -28,6 +28,24 @@ func init() {
 }
 
 func runParse(cmd *cobra.Command, args []string) (retErr error) {
+	defer func() {
+		v := recover()
+		if v != nil {
+			err, ok := v.(error)
+			if !ok {
+				retErr = fmt.Errorf("an unexpected error occurred: %v\n", v)
+				fmt.Fprintln(os.Stderr, retErr)
+				return
+			}
+
+			retErr = err
+		}
+
+		if retErr != nil {
+			fmt.Fprintln(os.Stderr, retErr)
+		}
+	}()
+
 	cgram, err := readCompiledGrammar(args[0])
 	if err != nil {
 		return fmt.Errorf("Cannot read a compiled grammar: %w", err)
diff --git a/cmd/vartan/root.go b/cmd/vartan/root.go
index ad163a6..a193577 100644
--- a/cmd/vartan/root.go
+++ b/cmd/vartan/root.go
@@ -1,9 +1,6 @@
 package main
 
 import (
-	"fmt"
-	"os"
-
 	"github.com/spf13/cobra"
 )
 
@@ -19,10 +16,5 @@ var rootCmd = &cobra.Command{
 }
 
 func Execute() error {
-	err := rootCmd.Execute()
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "%v\n", err)
-		return err
-	}
-	return nil
+	return rootCmd.Execute()
 }
diff --git a/error/error.go b/error/error.go
index 1745c52..cc4fed5 100644
--- a/error/error.go
+++ b/error/error.go
@@ -1,15 +1,55 @@
 package error
 
-import "fmt"
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
 
 type SpecError struct {
-	Cause error
-	Row   int
+	Cause      error
+	FilePath   string
+	SourceName string
+	Row        int
 }
 
 func (e *SpecError) Error() string {
-	if e.Row == 0 {
-		return fmt.Sprintf("error: %v", e.Cause)
+	var b strings.Builder
+	if e.SourceName != "" {
+		fmt.Fprintf(&b, "%v: ", e.SourceName)
 	}
-	return fmt.Sprintf("%v: error: %v", e.Row, e.Cause)
+	if e.Row != 0 {
+		fmt.Fprintf(&b, "%v: ", e.Row)
+	}
+	fmt.Fprintf(&b, "error: %v", e.Cause)
+
+	line := readLine(e.FilePath, e.Row)
+	if line != "" {
+		fmt.Fprintf(&b, "\n    %v", line)
+	}
+
+	return b.String()
+}
+
+func readLine(filePath string, row int) string {
+	if filePath == "" || row <= 0 {
+		return ""
+	}
+
+	f, err := os.Open(filePath)
+	if err != nil {
+		return ""
+	}
+
+	i := 1
+	s := bufio.NewScanner(f)
+	for s.Scan() {
+		if i == row {
+			return s.Text()
+		}
+		i++
+	}
+
+	return ""
 }