Enforce attribute targets on functions

docs/release-notes/.FSharp.Compiler.Service/8.0.300.md

@@ -11,6 +11,7 @@
 * `[<CliEvent>]` member should not produce property symbol. ([Issue #16640](https://github.com/dotnet/fsharp/issues/16640), [PR #16658](https://github.com/dotnet/fsharp/pull/16658))
 * Fix discriminated union initialization. ([#PR 16661](https://github.com/dotnet/fsharp/pull/16661))
 * Allow calling method with both Optional and ParamArray. ([#PR 16688](https://github.com/dotnet/fsharp/pull/16688), [suggestions #1120](https://github.com/fsharp/fslang-suggestions/issues/1120))
+* Enforce AttributeTargets on let values and functions. ([PR #16692](https://github.com/dotnet/fsharp/pull/16692))
 
 ### Added
 

docs/release-notes/.Language/preview.md

@@ -8,7 +8,8 @@
 ### Fixed
 
 * Allow extension methods without type attribute work for types from imported assemblies. ([PR #16368](https://github.com/dotnet/fsharp/pull/16368))
+* Enforce AttributeTargets on let values and functions. ([PR #16692](https://github.com/dotnet/fsharp/pull/16692))
 
 ### Changed
 
-* Lower interpolated strings to string concatenation. ([PR #16556](https://github.com/dotnet/fsharp/pull/16556))
+* Lower interpolated strings to string concatenation. ([PR #16556](https://github.com/dotnet/fsharp/pull/16556))

src/Compiler/Checking/CheckExpressions.fs

@@ -10636,8 +10636,7 @@ and TcNormalizedBinding declKind (cenv: cenv) env tpenv overallTy safeThisValOpt
             | ModuleOrMemberBinding, SynBindingKind.StandaloneExpression, _ -> Some(".cctor")
             | _, _, _ -> envinner.eCallerMemberName
 
-        let envinner = {envinner with eCallerMemberName = callerName }
-
+        let envinner = { envinner with eCallerMemberName = callerName }
         let attrTgt = declKind.AllowedAttribTargets memberFlagsOpt
 
         let isFixed, rhsExpr, overallPatTy, overallExprTy =
@@ -10873,6 +10872,16 @@ and TcNormalizedBinding declKind (cenv: cenv) env tpenv overallTy safeThisValOpt
                 errorR(Error(FSComp.SR.tcLiteralCannotBeInline(), mBinding))
             if not (isNil declaredTypars) then
                 errorR(Error(FSComp.SR.tcLiteralCannotHaveGenericParameters(), mBinding))
+
+        if g.langVersion.SupportsFeature(LanguageFeature.EnforceAttributeTargetsOnFunctions) && memberFlagsOpt.IsNone && not attrs.IsEmpty then
+            let rhsIsFunction = isFunTy g overallPatTy
+            let lhsIsFunction = isFunTy g overallExprTy
+            let attrTgt =
+                match rhsIsFunction, lhsIsFunction with
+                | false, false when declaredTypars.IsEmpty -> AttributeTargets.Field ||| AttributeTargets.Property ||| AttributeTargets.ReturnValue
+                | _, _ -> AttributeTargets.Method ||| AttributeTargets.ReturnValue
+
+            TcAttributesWithPossibleTargets false cenv env attrTgt attrs |> ignore
 
         CheckedBindingInfo(inlineFlag, valAttribs, xmlDoc, tcPatPhase2, explicitTyparInfo, nameToPrelimValSchemeMap, rhsExprChecked, argAndRetAttribs, overallPatTy, mBinding, debugPoint, isCompGen, literalValue, isFixed), tpenv
 

src/Compiler/Checking/TailCallChecks.fs

@@ -725,12 +725,7 @@ let CheckModuleBinding cenv (isRec: bool) (TBind _ as bind) =
 
     // warn for non-rec functions which have the attribute
     if cenv.g.langVersion.SupportsFeature LanguageFeature.WarningWhenTailCallAttrOnNonRec then
-        let isNotAFunction =
-            match bind.Var.ValReprInfo with
-            | Some info -> info.HasNoArgs
-            | _ -> false
-
-        if (not isRec || isNotAFunction) && cenv.g.HasTailCallAttrib bind.Var.Attribs then
+        if not isRec && cenv.g.HasTailCallAttrib bind.Var.Attribs then
             warning (Error(FSComp.SR.chkTailCallAttrOnNonRec (), bind.Var.Range))
 
     // Check if a let binding to the result of a rec expression is not inside the rec expression

src/Compiler/FSComp.txt

@@ -1594,6 +1594,7 @@ featureWarningIndexedPropertiesGetSetSameType,"Indexed properties getter and set
 featureChkTailCallAttrOnNonRec,"Raises warnings if the 'TailCall' attribute is used on non-recursive functions."
 featureUnionIsPropertiesVisible,"Union case test properties"
 featureBooleanReturningAndReturnTypeDirectedPartialActivePattern,"Boolean-returning and return-type-directed partial active patterns"
+featureEnforceAttributeTargetsOnFunctions,"Enforce AttributeTargets on functions"
 featureLowerInterpolatedStringToConcat,"Optimizes interpolated strings in certain cases, by lowering to concatenation"
 3354,tcNotAFunctionButIndexerNamedIndexingNotYetEnabled,"This value supports indexing, e.g. '%s.[index]'. The syntax '%s[index]' requires /langversion:preview. See https://aka.ms/fsharp-index-notation."
 3354,tcNotAFunctionButIndexerIndexingNotYetEnabled,"This expression supports indexing, e.g. 'expr.[index]'. The syntax 'expr[index]' requires /langversion:preview. See https://aka.ms/fsharp-index-notation."

src/Compiler/Facilities/LanguageFeatures.fs

@@ -85,6 +85,7 @@ type LanguageFeature =
     | WarningIndexedPropertiesGetSetSameType
     | WarningWhenTailCallAttrOnNonRec
     | BooleanReturningAndReturnTypeDirectedPartialActivePattern
+    | EnforceAttributeTargetsOnFunctions
     | LowerInterpolatedStringToConcat
 
 /// LanguageVersion management
@@ -198,6 +199,7 @@ type LanguageVersion(versionText) =
                 LanguageFeature.WarningWhenTailCallAttrOnNonRec, previewVersion
                 LanguageFeature.UnionIsPropertiesVisible, previewVersion
                 LanguageFeature.BooleanReturningAndReturnTypeDirectedPartialActivePattern, previewVersion
+                LanguageFeature.EnforceAttributeTargetsOnFunctions, previewVersion
                 LanguageFeature.LowerInterpolatedStringToConcat, previewVersion
             ]
 
@@ -342,6 +344,7 @@ type LanguageVersion(versionText) =
         | LanguageFeature.WarningWhenTailCallAttrOnNonRec -> FSComp.SR.featureChkTailCallAttrOnNonRec ()
         | LanguageFeature.BooleanReturningAndReturnTypeDirectedPartialActivePattern ->
             FSComp.SR.featureBooleanReturningAndReturnTypeDirectedPartialActivePattern ()
+        | LanguageFeature.EnforceAttributeTargetsOnFunctions -> FSComp.SR.featureEnforceAttributeTargetsOnFunctions ()
         | LanguageFeature.LowerInterpolatedStringToConcat -> FSComp.SR.featureLowerInterpolatedStringToConcat ()
 
     /// Get a version string associated with the given feature.

src/Compiler/Facilities/LanguageFeatures.fsi

@@ -76,6 +76,7 @@ type LanguageFeature =
     | WarningIndexedPropertiesGetSetSameType
     | WarningWhenTailCallAttrOnNonRec
     | BooleanReturningAndReturnTypeDirectedPartialActivePattern
+    | EnforceAttributeTargetsOnFunctions
     | LowerInterpolatedStringToConcat
 
 /// LanguageVersion management