From a443f0a1a4b79faa0b0271b72ea4a8e5f3d03ffd Mon Sep 17 00:00:00 2001
From: Ryo Nihei <nihei.dev@gmail.com>
Date: Sat, 14 May 2022 14:42:00 +0900
Subject: Prohibit applying the expansion operator to anything other than
 identifiers

---
 spec/parser.go       |  8 ++++++--
 spec/parser_test.go  | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 spec/syntax_error.go |  2 ++
 3 files changed, 62 insertions(+), 2 deletions(-)

(limited to 'spec')

diff --git a/spec/parser.go b/spec/parser.go
index 9c66bfb..efbd072 100644
--- a/spec/parser.go
+++ b/spec/parser.go
@@ -494,10 +494,14 @@ func (p *parser) parseParameter() *ParameterNode {
 			Group: g,
 			Pos:   pos,
 		}
-	default:
-		return nil
 	}
 	if p.consume(tokenKindExpantion) {
+		switch {
+		case param == nil:
+			raiseSyntaxError(p.pos.Row, synErrStrayExpOp)
+		case param.ID == "":
+			raiseSyntaxError(p.pos.Row, synErrInvalidExpOperand)
+		}
 		param.Expansion = true
 	}
 	return param
diff --git a/spec/parser_test.go b/spec/parser_test.go
index 15f1330..c7d43de 100644
--- a/spec/parser_test.go
+++ b/spec/parser_test.go
@@ -598,6 +598,60 @@ bar: "bar";
 				},
 			},
 		},
+		{
+			caption: "an expansion operator must be preceded by an identifier",
+			src: `
+s
+    : foo #ast ...
+    ;
+`,
+			synErr: synErrStrayExpOp,
+		},
+		{
+			caption: "an expansion operator must be preceded by an identifier",
+			src: `
+a
+    : foo #ast ... foo
+    ;
+`,
+			synErr: synErrStrayExpOp,
+		},
+		{
+			caption: "an expansion operator cannot be applied to a pattern",
+			src: `
+a
+    : "foo" #ast "foo"...
+    ;
+`,
+			synErr: synErrInvalidExpOperand,
+		},
+		{
+			caption: "an expansion operator cannot be applied to a string",
+			src: `
+a
+    : 'foo' #ast 'foo'...
+    ;
+`,
+			synErr: synErrInvalidExpOperand,
+		},
+		{
+			caption: "an expansion operator cannot be applied to an ordered symbol",
+			src: `
+a
+    : foo #ast $foo...
+    ;
+`,
+			synErr: synErrInvalidExpOperand,
+		},
+		{
+			caption: "an expansion operator cannot be applied to a directive group",
+			src: `
+a
+    : foo #ast ()...
+    ;
+`,
+			synErr: synErrInvalidExpOperand,
+		},
 		{
 			caption: "an AST has node positions",
 			src: `
diff --git a/spec/syntax_error.go b/spec/syntax_error.go
index cf64e75..db4c381 100644
--- a/spec/syntax_error.go
+++ b/spec/syntax_error.go
@@ -37,6 +37,8 @@ var (
 	synErrNoDirectiveName        = newSyntaxError("a directive needs a name")
 	synErrNoOrderedSymbolName    = newSyntaxError("an ordered symbol name is missing")
 	synErrUnclosedDirGroup       = newSyntaxError("a directive group must be closed by )")
+	synErrStrayExpOp             = newSyntaxError("an expansion operator ... must be preceded by an identifier")
+	synErrInvalidExpOperand      = newSyntaxError("an expansion operator ... can be applied to only an identifier")
 	synErrSemicolonNoNewline     = newSyntaxError("a semicolon must be followed by a newline")
 	synErrFragmentNoPattern      = newSyntaxError("a fragment needs one pattern element")
 )
-- 
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