Issue #20331 has been updated by tenderlovemaking (Aaron Patterson). I think it's important for the parser to expose these warnings. If someone uses the parser / AST for building a language server, then it's important to show warnings to the user _without_ running the code. In general, I think it's important to provide as many warnings and errors as possible statically so that language servers can show them to users. ---------------------------------------- Feature #20331: Should parser warn hash duplication and when clause? https://bugs.ruby-lang.org/issues/20331#change-107200 * Author: yui-knk (Kaneko Yuichiro) * Status: Open ---------------------------------------- # Background Right now, parser warns duplicated hash keys (#1) and when clause (#2). For example, ```ruby {1 => :a, 1 => :b} # => warning: key 1 is duplicated and overwritten on line 1 ``` ```ruby case 2 when 1, 1 else end # => test.rb:2: warning: duplicated `when' clause with line 2 is ignored ``` The parser compares different cardinality numbers. ```ruby { 1 => :a, 0x1 => :b, 0b1 => :b, 0d1 => :b, 0o1 => :b, } # => test.rb:2: warning: key 1 is duplicated and overwritten on line 3 # => test.rb:3: warning: key 1 is duplicated and overwritten on line 4 # => test.rb:4: warning: key 1 is duplicated and overwritten on line 5 # => test.rb:5: warning: key 1 is duplicated and overwritten on line 6 ``` # Problem Currently this is implemeted by converting string like `"123"` to Ruby Object and compare them. It's needed to remove Ruby Object from parse.y for Universal Parser. I created PR https://github.com/ruby/ruby/pull/10079 which implements bignum for parse.y without dependency on Ruby Object, however nobu and mame express concern about the cost and benefit of implmenting bignum for parser. I want to discuss which is the best approach for this problem. By the way, it's needed to calculate irreducible fraction for Rational key if we will keep warning messages. ```ruby $ ruby -wc -e '{10.2r => :a, 10.2r => :b}' -e:1: warning: key (51/5) is duplicated and overwritten on line 1 -e:1: warning: unused literal ignored Syntax OK ``` # Options ## 1. Warnings on parser Pros: * Users of Universal Parser don't need to implement warnings by themselves. I guess developers of other Ruby implementation may get benefit of reducing their effort. * Warnings are shown by `ruby -wc`. Cons: * We need to maintain bignum implementation for parser. There are two approaches for this option. ### 1-1. Implement bignum for parser The PR is this approach, implementing sub set of Ruby bignum for parser. ### 1-2. Extract existing bignum implementation then use it Make existing bignum implementation to be independent of Ruby Object and use it from both bignum.c and parse.y. ## 2. Moving warnings logic into compile phase We can use Ruby Object in compile.c. Then moving the logic into compile.c solves this problem. Pros: * No need to implement bignum for parser. Cons: * Users of Universal Parser need to implement warnings by themselves. * Warnings are not shown by `ruby -wc`. -- https://bugs.ruby-lang.org/