Disallow calling abstract methods directly on interfaces (#17021)

* Disallow calling abstract methods directly on interfaces

* More tests

* IWSAMs are not supported by NET472

* Update src/Compiler/Checking/ConstraintSolver.fs

Co-authored-by: Tomas Grosup <[email protected]>

* fix typos

* looking for the right check

* Add comments

* move release notes

* Add a new error number and message

* Update docs/release-notes/.FSharp.Compiler.Service/8.0.400.md

Co-authored-by: Brian Rourke Boll <[email protected]>

* Update docs/release-notes/.FSharp.Compiler.Service/8.0.400.md

Co-authored-by: Brian Rourke Boll <[email protected]>

* Improve error message

---------

Co-authored-by: Tomas Grosup <[email protected]>
Co-authored-by: Brian Rourke Boll <[email protected]>

Author: 3 people

docs/release-notes/.FSharp.Compiler.Service/8.0.400.md

@@ -1,5 +1,6 @@
 ### Fixed
 
-* Various parenthesization API fixes. ([PR #16977](https://github.com/dotnet/fsharp/pull/16977)) 
+* Disallow calling abstract methods directly on interfaces. ([Issue #14012](https://github.com/dotnet/fsharp/issues/14012), [Issue #16299](https://github.com/dotnet/fsharp/issues/16299), [PR #17021](https://github.com/dotnet/fsharp/pull/17021))
+* Various parenthesization API fixes. ([PR #16977](https://github.com/dotnet/fsharp/pull/16977))
 * Fix bug in optimization of for-loops over integral ranges with steps and units of measure. ([Issue #17025](https://github.com/dotnet/fsharp/issues/17025), [PR #17040](https://github.com/dotnet/fsharp/pull/17040))
 * Fix calling an overridden virtual static method via the interface ([PR #17013](https://github.com/dotnet/fsharp/pull/17013))

src/Compiler/Checking/ConstraintSolver.fs

@@ -2942,10 +2942,23 @@ and ResolveOverloading
     let candidates = calledMethGroup |> List.filter (fun cmeth -> cmeth.IsCandidate(m, ad))
 
     let calledMethOpt, errors, calledMethTrace = 
-
         match calledMethGroup, candidates with 
-        | _, [calledMeth] when not isOpConversion -> 
-            Some calledMeth, CompleteD, NoTrace
+        | _, [calledMeth] when not isOpConversion ->
+            // See what candidates we have based on static/virtual/abstract
+            
+            // If false then is a static method call directly on an interface e.g.
+            // IParsable.Parse(...)
+            // IAdditionOperators.(+)
+            // This is not allowed as Parse and (+) method are static abstract
+            let isStaticConstrainedCall =
+                match calledMeth.OptionalStaticType with
+                | Some ttype -> isTyparTy g ttype
+                | None -> false
+                
+            match calledMeth.Method with
+            | ILMeth(ilMethInfo= ilMethInfo) when not isStaticConstrainedCall && ilMethInfo.IsStatic && ilMethInfo.IsAbstract ->
+                None, ErrorD (Error (FSComp.SR.chkStaticAbstractInterfaceMembers(ilMethInfo.ILName), m)), NoTrace
+            | _ -> Some calledMeth, CompleteD, NoTrace
 
         | [], _ when not isOpConversion -> 
             None, ErrorD (Error (FSComp.SR.csMethodNotFound(methodName), m)), NoTrace

src/Compiler/FSComp.txt

@@ -1745,4 +1745,5 @@ featureReuseSameFieldsInStructUnions,"Share underlying fields in a [<Struct>] di
 3862,parsStaticMemberImcompleteSyntax,"Incomplete declaration of a static construct. Use 'static let','static do','static member' or 'static val' for declaration."
 3863,parsExpectingField,"Expecting record field"
 3864,tooManyMethodsInDotNetTypeWritingAssembly,"The type '%s' has too many methods. Found: '%d', maximum: '%d'"
-3865,parsOnlySimplePatternsAreAllowedInConstructors,"Only simple patterns are allowed in primary constructors"
+3865,parsOnlySimplePatternsAreAllowedInConstructors,"Only simple patterns are allowed in primary constructors"
+3866,chkStaticAbstractInterfaceMembers,"A static abstract non-virtual interface member should only be called via type parameter (for example: 'T.%s)."