Add error symbol and #recover directive to recover from an error state

1 files changed, 130 insertions, 0 deletions

diff --git a/driver/syntax_error_test.go b/driver/syntax_error_test.go
new file mode 100644
index 0000000..427f0d1
--- /dev/null
+++ b/driver/syntax_error_test.go
@@ -0,0 +1,130 @@
+package driver
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/nihei9/vartan/grammar"
+	"github.com/nihei9/vartan/spec"
+)
+
+func TestParserWithSyntaxErrors(t *testing.T) {
+	tests := []struct {
+		caption     string
+		specSrc     string
+		src         string
+		synErrCount int
+	}{
+		{
+			caption: "the parser can report a syntax error",
+			specSrc: `
+s
+    : foo
+    ;
+
+foo: 'foo';
+`,
+			src:         `bar`,
+			synErrCount: 1,
+		},
+		{
+			caption: "when the parser reduced a production having the reduce directive, the parser will recover from an error state",
+			specSrc: `
+seq
+    : seq elem ';'
+	| elem ';'
+	| error ';' #recover
+	;
+elem
+    : a b c
+	;
+
+ws: "[\u{0009}\u{0020}]+" #skip;
+a: 'a';
+b: 'b';
+c: 'c';
+`,
+			src:         `!; a!; ab!;`,
+			synErrCount: 3,
+		},
+		{
+			caption: "After the parser shifts the error symbol, symbols are ignored until a symbol the parser can perform shift appears",
+			specSrc: `
+seq
+    : seq elem ';'
+	| elem ';'
+	| error ';' #recover
+	;
+elem
+    : a b c
+	;
+
+ws: "[\u{0009}\u{0020}]+" #skip;
+a: 'a';
+b: 'b';
+c: 'c';
+`,
+			// After the parser trasits to the error state reading the first invalid symbol ('!'),
+			// the second and third invalid symbols ('!') are ignored.
+			src:         `! ! !; a!; ab!;`,
+			synErrCount: 3,
+		},
+		{
+			caption: "when the parser performs shift three times, the parser recovers from the error state",
+			specSrc: `
+seq
+    : seq elem ';'
+	| elem ';'
+	| error '*' '*' ';'
+	;
+elem
+    : a b c
+	;
+
+ws: "[\u{0009}\u{0020}]+" #skip;
+a: 'a';
+b: 'b';
+c: 'c';
+`,
+			src:         `!**; a!**; ab!**; abc!`,
+			synErrCount: 4,
+		},
+	}
+	for i, tt := range tests {
+		t.Run(fmt.Sprintf("#%v", i), func(t *testing.T) {
+			ast, err := spec.Parse(strings.NewReader(tt.specSrc))
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			b := grammar.GrammarBuilder{
+				AST: ast,
+			}
+			g, err := b.Build()
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			gram, err := grammar.Compile(g, grammar.SpecifyClass(grammar.ClassLALR))
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			p, err := NewParser(gram, strings.NewReader(tt.src), MakeAST(), MakeCST())
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			err = p.Parse()
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			synErrs := p.SyntaxErrors()
+			if len(synErrs) != tt.synErrCount {
+				t.Fatalf("unexpected syntax error; want: %v error(s), got: %v error(s)", tt.synErrCount, len(synErrs))
+			}
+		})
+	}
+}