Super spread errors part 2 #1973
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chenglou
reviewed
May 30, 2018
src/reason-parser/reason_parser.mly
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| @@ -1036,6 +1036,22 @@ let raise_record_trailing_semi_error loc = | |||
| let msg = "Record entries are separated by comma; we've found a semicolon instead." in | |||
| raise Reason_syntax_util.(Error(loc, (Syntax_error msg))) | |||
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| let record_exp_spread_msg = | |||
| "Records can only have one `...` spread, at the beginning" | |||
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Don't forget the period at the end!
Records can only have one `...` spread, at the beginning.
Explanation: since records have a known, fixed shape, a spread like `{a, ...b}` wouldn't make sense, as `b` would override every field of `a` anyway.
src/reason-parser/reason_parser.mly
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| "Records can only have one `...` spread, at the beginning" | ||
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| let record_pat_spread_msg = | ||
| "The `...` spread operator is not supported in record pattern matches" |
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Record's `...` spread is not supported in pattern matches.
Explanation: you can't collect a subset of a record's field into its own record, since a record needs an explicit declaration and that subset wouldn't have one.
Solution: you need to pull out each field you want explicitly.
src/reason-parser/reason_parser.mly
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| lseparated_list(COMMA, opt_spread(expr_optional_constraint)) | ||
| COMMA? | ||
| BARRBRACKET | ||
| { let msg = "Arrays can not use the `...` spread. Arrays in Reason are fixed length and spreading them would allocate a new array." in |
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Arrays can't use the `...` spread currently. Please use `concat` or other Array helpers.
src/reason-parser/reason_parser.mly
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| (* If the `...` appears in any other location then the last, | ||
| * show a friendly, clear message explaining the consequences. *) | ||
| let msg = "Lists can only have one `...` spread, and at the end. | ||
| let msg = "Lists can only have one `...` spread, and at the end. |
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Sorry could you change this one to remove and? The comma is probably enough to disambiguate meaning here.
src/reason-parser/reason_parser.mly
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| raise Reason_syntax_util.(Error(dotdotdotLoc, (Syntax_error msg))) | ||
| | None -> e | ||
| ) es in | ||
| Solution: directly use `concat`." in |
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Could you also change this one too:
Solution: directly use `concat` or other List helpers.
(I wrote it that way for List and Array because concat is shared by stdlib and Belt, but have different meanings. In reality you'd use List.append or Belt.List.concat, or List.concat or Belt.List.concatMany.)
src/reason-parser/reason_parser.mly
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| @@ -3701,22 +3702,42 @@ mark_position_pat | |||
| ; | |||
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| %inline pattern_comma_list: | |||
| lseparated_nonempty_list(COMMA, pattern) { $1 }; | |||
| lseparated_nonempty_list(COMMA, opt_spread(pattern)) | |||
| { let msg = "Pattern matching on arrays can not have a `...` spread. It would allocate a whole new array every time." in | |||
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Array's `...` spread is not supported in pattern matches.
Explanation: such spread would create a subarray; out of performance concern, our pattern matching currently guarantees to never create new intermediate data.
Solution: if it's to validate the first few elements, use a `when` clause + Array size check + `get` checks on the current pattern. If it's to obtain a subarray, use `Array.sub` or `Belt.Array.slice`.
src/reason-parser/reason_parser.mly
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| | Some dotdotdotLoc -> (ps, Some p) | ||
| | None -> (hd::ps, None) | ||
| in | ||
| let msg = "Pattern matching on a list can only have one `...` spread, and at the end" in |
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List pattern matches only supports one `...` spread, at the end.
Explanation: a list spread at the tail is efficient, but a spread in the middle would create new list(s); out of performance concern, our pattern matching currently guarantees to never create new intermediate data.
added 3 commits
May 31, 2018 07:32
-Arrays (expressions + patterns) -List (patterns) -Records (expressions + patterns)
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Fixes #1952
-Arrays (expressions + patterns)
-List (expressions + patterns)
-Records (expressions + patterns)