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This is a follow up from https://github.com/nushell/nushell/pull/7540. Please provide feedback if you have the time! ## Summary This PR lets you use `?` to indicate that a member in a cell path is optional and Nushell should return `null` if that member cannot be accessed. Unlike the previous PR, `?` is now a _postfix_ modifier for cell path members. A cell path of `.foo?.bar` means that `foo` is optional and `bar` is not. `?` does _not_ suppress all errors; it is intended to help in situations where data has "holes", i.e. the data types are correct but something is missing. Type mismatches (like trying to do a string path access on a date) will still fail. ### Record Examples ```bash { foo: 123 }.foo # returns 123 { foo: 123 }.bar # errors { foo: 123 }.bar? # returns null { foo: 123 } | get bar # errors { foo: 123 } | get bar? # returns null { foo: 123 }.bar.baz # errors { foo: 123 }.bar?.baz # errors because `baz` is not present on the result from `bar?` { foo: 123 }.bar.baz? # errors { foo: 123 }.bar?.baz? # returns null ``` ### List Examples ``` 〉[{foo: 1} {foo: 2} {}].foo Error: nu:🐚:column_not_found × Cannot find column ╭─[entry #30:1:1] 1 │ [{foo: 1} {foo: 2} {}].foo · ─┬ ─┬─ · │ ╰── cannot find column 'foo' · ╰── value originates here ╰──── 〉[{foo: 1} {foo: 2} {}].foo? ╭───┬───╮ │ 0 │ 1 │ │ 1 │ 2 │ │ 2 │ │ ╰───┴───╯ 〉[{foo: 1} {foo: 2} {}].foo?.2 | describe nothing 〉[a b c].4? | describe nothing 〉[{foo: 1} {foo: 2} {}] | where foo? == 1 ╭───┬─────╮ │ # │ foo │ ├───┼─────┤ │ 0 │ 1 │ ╰───┴─────╯ ``` # Breaking changes 1. Column names with `?` in them now need to be quoted. 2. The `-i`/`--ignore-errors` flag has been removed from `get` and `select` 1. After this PR, most `get` error handling can be done with `?` and/or `try`/`catch`. 4. Cell path accesses like this no longer work without a `?`: ```bash 〉[{a:1 b:2} {a:3}].b.0 2 ``` We had some clever code that was able to recognize that since we only want row `0`, it's OK if other rows are missing column `b`. I removed that because it's tricky to maintain, and now that query needs to be written like: ```bash 〉[{a:1 b:2} {a:3}].b?.0 2 ``` I think the regression is acceptable for now. I plan to do more work in the future to enable streaming of cell path accesses, and when that happens I'll be able to make `.b.0` work again. |
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