Duplicate rule name generates faulty Go-code. Should throw an error

[prydin]

If you accidentally define two rules with the same name, the parser generator will generate faulty code making it very difficult to troubleshoot. It should throw an error instead.

Example grammar:

#go:build grammars
# +build grammars

package experiments

type Test Peg {}

Expression <-
    FOO { fmt.Println("FOO") }
    BAR { fmt.Println("BAR") } !.

FOO <- "foo"
BAR <- "bar"
FOO <- "foo"

More specifically, the parser generator seems to omit one of the rules from the rule array, causing subsequent indices to mismatch and the wrong rules being invoked.