Allow dot property access on union of objects with undeclared property

[anthony-c-martin]

Closes #14059

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 9066237433)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 9066237433

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 9066237433"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 9066237433

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 9066237433"

[github-actions]

Dotnet Test Results

    63 files   -     36      63 suites   - 36   22m 56s ⏱️ - 8m 44s
10 888 tests  -     17  10 887 ✅  -     17  1 💤 ±0  0 ❌ ±0 
25 537 runs   - 12 958  25 535 ✅  - 12 957  2 💤  - 1  0 ❌ ±0 

Results for commit 808c67c. ± Comparison against base commit 68462f0.

♻️ This comment has been updated with latest results.

[anthony-c-martin]

@jeskew what are your thoughts on the risk here?

[jeskew]

I think we do want to use an explicit null, since we have linters that will propose a fix from <base>.<property> to <base>.?<property> if the property has a type like string | null. But this should only occur if <base> is an object. So the type of foo.bar should be the following (mapping typeof(foo) => typeof(foo.bar)):

• { bar: string } | { bar: int } => string | int
• { bar: string } | {} => string | null
• { otherProp: string } | { otherProp: int } => error
• { bar: string } | string => error

Like you say in the comment, though, we can use any now and refine it later if you want to get this out immediately.

[anthony-c-martin]

Thanks! I think I'd like to leave it more permissive for now, because making this change breaks the 2 samples given in the issue report.

In particular, this becomes quite annoying to handle:

var items = [
  { obj: 1 }
  { obj: 2 }
  { obj: 3 }
  { obj: 4 }
  { obj: 5, x: 5 }
]
var s = sort(
  filter(
    map(items, x => x.obj < 2 ? { order: 1, value: x } : x.obj > 4 ? { order: 2, value: x } : {}),
    x => !(empty(x))
  ),
  (arg1, arg2) => arg1.order < arg2.order
)

Because the impact on types of !(empty(x)) isn't understood by the filter function, you end up having to do a lot of work in the sort function - e.g. I think you'd either need (arg1, arg2) => any(arg1).order < any(arg2).order or (arg1, arg2) => (arg1.?order ?? 0) < (arg2.?order ?? 0)