Add testing for the driver

The driver can reduce productions that have the empty alternative and can generate a CST (and AST) node.

2 files changed, 47 insertions, 0 deletions

diff --git a/driver/parser.go b/driver/parser.go
index 7b6df7b..fa89fcf 100644
--- a/driver/parser.go
+++ b/driver/parser.go
@@ -121,8 +121,11 @@ func (p *Parser) Parse() error {
 			}
 
 			// semantic action
+
 			prodNum := act
 			lhs := p.gram.ParsingTable.LHSSymbols[prodNum]
+
+			// When an alternative is empty, `n` will be 0, and `handle` will be empty slice.
 			n := p.gram.ParsingTable.AlternativeSymbolCounts[prodNum]
 			handle := p.semStack[len(p.semStack)-n:]
 
diff --git a/driver/parser_test.go b/driver/parser_test.go
index 8713893..3dec508 100644
--- a/driver/parser_test.go
+++ b/driver/parser_test.go
@@ -104,6 +104,50 @@ id: "[A-Za-z_][0-9A-Za-z_]*";
 				),
 			),
 		},
+		// The driver can reduce productions that have the empty alternative and can generate a CST (and AST) node.
+		{
+			specSrc: `
+s
+    : foo bar
+    ;
+foo
+    :
+    ;
+bar
+    : bar_text
+    |
+    ;
+bar_text: "bar";
+`,
+			src: ``,
+			cst: nonTermNode("s",
+				termNode("foo", ""),
+				termNode("bar", ""),
+			),
+		},
+		// The driver can reduce productions that have the empty alternative and can generate a CST (and AST) node.
+		{
+			specSrc: `
+s
+    : foo bar
+    ;
+foo
+    :
+    ;
+bar
+    : bar_text
+    |
+    ;
+bar_text: "bar";
+`,
+			src: `bar`,
+			cst: nonTermNode("s",
+				termNode("foo", ""),
+				nonTermNode("bar",
+					termNode("bar_text", "bar"),
+				),
+			),
+		},
 		{
 			specSrc: `
 mode_tran_seq