json: Fix panic when parsing malformed JSON

json/public_test.go

@@ -1,6 +1,7 @@
 package json
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/hashicorp/hcl/v2"
@@ -95,3 +96,19 @@ func TestParseTemplateUnwrap(t *testing.T) {
 		t.Errorf("wrong result %#v; want %#v", val, cty.True)
 	}
 }
+
+func TestParse_malformed(t *testing.T) {
+	src := `{
+  "http_proxy_url: "http://xxxxxx",
+}`
+	file, diags := Parse([]byte(src), "")
+	if got, want := len(diags), 2; got != want {
+		t.Errorf("got %d diagnostics; want %d", got, want)
+	}
+	if err, want := diags.Error(), `Missing property value colon`; !strings.Contains(err, want) {
+		t.Errorf("diags are %q, but should contain %q", err, want)
+	}
+	if file == nil {
+		t.Errorf("got nil File; want actual file")
+	}
+}

json/scanner.go

@@ -107,6 +107,15 @@ func scan(buf []byte, start pos) []token {
 			})
 			// If we've encountered an invalid then we might as well stop
 			// scanning since the parser won't proceed beyond this point.
+			// We insert a synthetic EOF marker here to match the expectations
+			// of consumers of this data structure.
+			p.Pos.Column++
+			p.Pos.Byte++
+			tokens = append(tokens, token{
+				Type:  tokenEOF,
+				Bytes: nil,
+				Range: posRange(p, p),
+			})
 			return tokens
 		}
 	}

json/scanner_test.go

@@ -829,6 +829,21 @@ func TestScan(t *testing.T) {
 						},
 					},
 				},
+				{
+					Type: tokenEOF,
+					Range: hcl.Range{
+						Start: hcl.Pos{
+							Byte:   1,
+							Line:   1,
+							Column: 2,
+						},
+						End: hcl.Pos{
+							Byte:   1,
+							Line:   1,
+							Column: 2,
+						},
+					},
+				},
 			},
 		},
 	}