Tracking Error reporting improvements

[isaacabraham]

Related to #1102, this issue could act as an overall list for all the issues relating to error reporting from the compiler. I'll start the ball rolling by adding the ones mentioned in that issue plus a few more.

Up for grabs!

• Improve error reporting: Use before definition within files and across whole project #12341
• Improve error reporting: suggest inlining when compiler constrains types to be less generic #1160
• Improve Error Reporting: "inner" expressions inside computations expressions #2739
• Improve error reporting: do-keyword missing in a query #2799
• Improve Error Reporting: Operator that has not been defined #2828
• Warning or error should be raised when alternative constructor calls itself #2321
• Improve Error Reporting: "could not be generalized because it would escape its scope" #3302
• Improve Error Reporting: Unnecessarily vague pattern match warning #3765
• Improve error message when yield! was used but yield is needed and vice versa #4233
• Wrong indentation in list comprehension leads to unhelpful error message #4232
• Improve error reporting: Trying to pass arguments to a simple value gives confusing error. #5476
• Better diagnostics when using "as alias" in binding without wrapping expression in parens #5259
• Improve Error Reporting: Forgetting | in anonymous record gives a confusing error message. #8127
• Improve errors for incorrect overloads used in custom operations #10167
• Improve error reporting: Missing "else" branch for if expression with elif #6873

More discussion / on hold

• Improve Error Reporting: Make Nullness Warning 3261 less intimidating - Part 2 #18171
• Improve Error Reporting: Make Nullness Warning 3261 less intimidating #18170
• Improve Error Reporting: help with ambiguity between subtraction and negation #13014
• Improve Error Reporting: Make FS0072 less intimidating. #13013
• Improve Error Reporting: Make FS0039 easier to read at a glance. #13012
• Improve error reporting: Function accidentally partially applied #1107
• Improve error reporting: Accidental use of , instead of ; as collection separator #1120
• Improve error reporting: add an url with more info for each warning/error #1136
• Improve error reporting: report visibility issue between two assemblies #1348
• Improve error reporting: Better heuristics for identifying the code line with a type error #1384
• Improve error reporting: property syntax can't be remembered #2277
• Improve error reporting: message when defining record with open brace on separate line #1826
• Improve error reporting: Match expressions with DUs missing parentheses around their tupled arguments #1511
• Improve error reporting: Warn when pipe operators are incorrectly indented #1442
• Reword or better explain unique names on Struct DUs #5236
• Improve error reporting: Need parentheses on arguments #5475
• Improve error reporting: Passing an argument to a function that is a result of a function call #6687
• Improve Error Reporting: no expression in computation expression #6717
• Improve error reporting: when type mismatch error involves a tuple, say it is a tuple #11234
• Improve error reporting: Fluent OO code fails if method argument application is not tied to the method name #12586
• Show overload candidates when passing wrong parameter names or types #10564
• Error reporting: improve TP static parameter error message to list available parameters. #11445

Implemented!

• Improve error reporting: ambiguous override method in object expression #1429
• Match statement with a patterns referring to an out of scope identifier give incomplete warning #6712
• Improve error reporting: Partially applied generic value vs function #1161
• Improve Error Reporting: Internal error with badly defined anonymous record #6872
• Language Parser: poor error recovery on faulty DU declaration / improve error reporting #11468
• Elm-like compiler errors for name resolution #1102
• Improve error reporting: Missing "else" branch for if expression #1104
• Improve error reporting: if / else branches return different types. #1105
• Improve error reporting: usage of '<-' operator on non mutable bindings #1110
• Improve error reporting: Accidental use of , instead of ; as record field separator #1122
• Improve error reporting: Wrong cast operator (:?> instead of :>) #1127
• Improve error reporting: provide better literal suffix description #1129
• Improve error reporting: Missing "else" branch for if / elif expression #1157
• Improve error reporting: Let as last line in block #1162
• Improve error reporting: Recursive async functions #1170
• Improve error reporting: Detect module declarations that incorrectly end with = #1214
• Show better error when using ref cell instead of not #1275
• Improve error reporting: Member implementation with tuple argument(s) #1203
• Improve Error Reporting: Show better error when using ref cell instead of not #1276
• Improve error reporting: property setter in constructor expression #1112
• Improve error reporting: Warning when expression result is ignored #1108
• Improve error reporting: No abstract method matching implementation #1232
• Improve Error Reporting: Record does not match type when using Record Expressions #1280
• Add type info to error - references #1574 #1834
• Improve error reporting: Warning when the result of a comparison is ignored #1109
• Improve error reporting: This expression was expected to have type 'A' but here has type 'A' #2561
• Improve error reporting: Missing , from object initializer #1218
• Warning for return type of statement in while loop should only indicate the last line #326
• Confusing and ambiguous error (FS0368) when implementing an interface with overloads #1905
• Improve error when record is used like a ctor #1933
• Improve error reporting: override method does not match abstract member #1430
• Wrong error "type is not structurally comparable" if some fields of a record definition are unresolvable #2268
• Unfixable FS0076 error from fsharpi when putting #r directive in .fs file #569
• Improve warning for ignored values in sequence expressions #4228
• Better expression errors #5114
• Improve Error Reporting: When implementation is missing necessary overrides, report a list of them #4982
• Improve Error Reporting: Better description for mismatched anonymous records. #8091
• Improve error reporting: Missing = on type declaration #1121
• Puzzling error message in case of wrong indentation inside computation expression #2201 (more discussion?)
• Improve error reporting: Accessing protected members within async blocks. #2307 (should still be open for more "complete" fix)
• Confusing error message for invalid member declaration #920
• Improve error reporting: using EntryPoint attribute in an F# script #1431

Rejected

• Improve error reporting: Smarter heuristics on incorrect return type of if / else branch #1106
• Improve error reporting: missing cast operator for subtype case #1128

Contributing

If you have ideas for other error messages, please adhere to the following standard for new issues: -

1. Title the issue "Improve Error Reporting: "

2. Each issue should have the following elements: -

   a. What - reproduction of the error through a code snippet and compiler error / warning.
   b. Why - why the current compiler error / warning is insufficient.
   c. How - how you would improve the current error / warning with an alternative example.

[enricosada]

i just want to add a ref to ocaml error reporting improvements, it's really nice

[isaacabraham]

Another good source for ideas of potential issues: http://fsharpforfunandprofit.com/troubleshooting-fsharp/

[vilinski]

Missing method XYFooBar --> may be you need an FSharp.Core redirect

[isaacabraham]

@vilinski can you raise an issue for this and maybe give a concrete example of where this happens?

[dsyme]

That's a good list.

I'd like to see each of the issues above have a few lines of justification addressing why we believe the error message is specifically a problem for beginners (e.g. they might be coming with expectations from Python or C#)

[isaacabraham]

@dsyme done.

[dsyme]

@isaacabraham One error you might like to consider is a much better error message when a C# or C++ programmer uses !expr to mean "not". F# interprets that at "dereference a ref cell".

Now, as of F# 4.0, the use of explicit ref cells is far less common because implicit promotion of let mutable is now so well supported. We could probably even consider deprecating the use of !expr as the default syntax and instead ask people to either use not expr or expr.Value.

But even without going that far, we could surely improve the error message for a misuse of !expr in the common case, asking people to use not expr instead (perhaps with parentheses as in not (f x))

Can I leave it to you to add the specific issue for this?

[forki]

@dsyme WIP: #1275

[isaacabraham]

@forki what's the status of #1109 and #1218? Any way we can unblock these?

[forki]

I need help from @dsyme - I already contacted him

2016-08-15 18:46 GMT+02:00 Isaac Abraham [email protected]:

@forki https://github.com/forki what's the status of #1109
#1109 and #1218
#1218? Any way we can
unblock these?

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[LyndonGingerich]

Is #1431 still in state "More discussion / on hold"? It is closed as completed.

[0101]

@LyndonGingerich it's done. I moved it into the Implemented list.

[jkone27]

sorry if this is a not relevant remark or already adressed, maybe is already adressed by one of the proposals, but checking Rust error messages now and they are really awesome

but maybe is the same already referenced here? support code previews? Rust is really nice on error messages
#14832

[ShalokShalom]

sorry if this is a not relevant remark or already adressed, maybe is already adressed by one of the proposals, but checking Rust error messages now and they are really awesome

but maybe is the same already referenced here? support code previews? Rust is really nice on error messages #14832

I know that we spoke about this in the F# Discord, and it was said that the implementation of something like this relies on dotnet tooling, that is still in the works.

[voronoipotato]

@vzarytovskii hello, I made a suggestion about a confusing error message fsharp/fslang-suggestions#1324 here. Bent redirected me here. Trying to make sure I do this right. Should this suggestion be an dotnet/fsharp issue here?

[vzarytovskii]

Yeah, I think diagnostics improvements are fine in this repo

[voronoipotato]

Okay I'll probably have to tackle this after work, running out of lunch time :), also could you fix the title :( improvenets should be improvements, I can't stop thinking about it. Unless it's a pun, in which case 'ha'.