Linter suggests to replace lambda operation expression with lambda function expression

[msoeken]

Describe the bug

Linter suggests to replace operation lambda expression with function lambda expression, even though this would not work, because the callable signature requires an operation.

To Reproduce

https://microsoft.github.io/qsharp/?code=H4sIAAAAAAAAE22QT0vDQBDF7%252FkUj542ElMKnhoqiFUU%252FIO24qHksE3XZKDZze5OLEXy3WXTYIt0LjPMm9%252BDeVQ3xjEWvElvnJN7n15kER2Xc5KlNp6p6JXINMpJJqPxSVwt2lpYjyne2jXxKk8gi14cNphd40MTx5j2HT8RANzLgoU2jEd%252FVze8F9bHCUbWo5A67NcKKgijOIt6YkdckR7wUF%252FGgUAakzR9UrrkKpjgEpOTo1C3L69LYf2KgpYnCGMeZ383XT91kE2z3Z%252Bwh0fEUtI2OA9EF3WnGTxL0uLfc61XsB6zIZOr%252FEAe40pgQy7ztm7eVUmelRMrm8dxhvEYO2d0OYWvTLvdIIRR0reCxE46Tbo8b%252FYg7MAXxjlV8BQbo%252Fw5vot%252BAVKAZZX0AQAA&profile=unrestricted

Expected behavior

No linter warning should appear.

Additional context

This is similar to #1661

[Manvi-Agrawal]

@msoeken I think this bug is interesting edge case which might be tricky to tackle. I think this is arising due to function being promoted to operation because of all able conversation rules on Q#. All functions are operations. But not all operations are functions.

The example involves a function invoking DumpOperation function being passed as lambda argument. According to my understanding DumpOperation does not work on real hardware. I understand that it might be a little inconvenient for simulation purposes and might require refactoring. Do you have some other practical example(s) in mind for real hardware?

What if somebody decides to create a operation CustomDumpOperation that only invokes DumpOperation function. And then passed CustomDumpOperation to a operation accepting operation as argument. Then it seems we shouldn't flag it as warning, am I correct? I wonder this might lead to a snow ball effect, encouraging more operations.

What if the CustomDumpOperation is required to be declared as an operation for only few operation calls. And it works perfectly fine as a function for other cases. Is the suggestion to gravitate towards allowing CustomDumpOperation as a operation. I am afraid this kind of defeats the purpose of this lint rule.

Given the fact that this is a lint rule which can be turned off, I believe the current implementation is good enough for regular usage. Some other potential ways to tackle this might be to offer an improved linting functionality: (I) like inclusion/exclusion rules for file paths for each lint, (ii) having an allow list for a function to be treated as a Operation. So, in this case we could instruct QDK to treat DumpOperation as operation so that we don't get the warning. Thoughts?

PS: sent from mobile, not responsible for autocorrect errors