AttributeTargets better error message

docs/release-notes/.FSharp.Compiler.Service/10.0.100.md

@@ -6,6 +6,7 @@
 
 * Fix parsing errors using anonymous records and units of measures ([PR #18543](https://github.com/dotnet/fsharp/pull/18543))
 * Fix parsing errors using anonymous records and code quotations ([PR #18603](https://github.com/dotnet/fsharp/pull/18603))
+* Better error message for attribute targets. ([PR #18641](https://github.com/dotnet/fsharp/pull/18641))
 * Fixed: Allow `return`, `return!`, `yield`, `yield!` type annotations without parentheses ([PR #18533](https://github.com/dotnet/fsharp/pull/18533))
 * Allow `let!` and `use!` type annotations without requiring parentheses ([PR #18508](https://github.com/dotnet/fsharp/pull/18508))
 * Fix find all references for F# exceptions ([PR #18565](https://github.com/dotnet/fsharp/pull/18565))

src/Compiler/Checking/Expressions/CheckExpressions.fs

@@ -143,6 +143,8 @@ exception StandardOperatorRedefinitionWarning of string * range
 
 exception InvalidInternalsVisibleToAssemblyName of badName: string * fileName: string option
 
+exception InvalidAttributeTargetForLanguageElement of elementTargets: string array * allowedTargets: string array * range: range
+
 //----------------------------------------------------------------------------------------------
 // Helpers for determining if/what specifiers a string has.
 // Used to decide if interpolated string can be lowered to a concat call.
@@ -11356,7 +11358,29 @@ and CheckAttributeUsage (g: TcGlobals) (mAttr: range) (tcref: TyconRef) (attrTgt
         if (directedTargets = AttributeTargets.Assembly || directedTargets = AttributeTargets.Module) then
             errorR(Error(FSComp.SR.tcAttributeIsNotValidForLanguageElementUseDo(), mAttr))
         else
-            warning(Error(FSComp.SR.tcAttributeIsNotValidForLanguageElement(), mAttr))
+            let attributeTargetsToString (targets: int) =
+                [|
+                    if targets &&& int AttributeTargets.Assembly <> 0 then "assembly"
+                    if targets &&& int AttributeTargets.Module <> 0 then "module"
+                    if targets &&& int AttributeTargets.Class <> 0 then "class"
+                    if targets &&& int AttributeTargets.Struct <> 0 then "struct"
+                    if targets &&& int AttributeTargets.Enum <> 0 then "enum"
+                    if targets &&& int AttributeTargets.Constructor <> 0 then "constructor"
+                    if targets &&& int AttributeTargets.Method <> 0 then "method"
+                    if targets &&& int AttributeTargets.Property <> 0 then "property"
+                    if targets &&& int AttributeTargets.Field <> 0 then "field"
+                    if targets &&& int AttributeTargets.Event <> 0 then "event"
+                    if targets &&& int AttributeTargets.Interface <> 0 then "interface"
+                    if targets &&& int AttributeTargets.Parameter <> 0 then "parameter"
+                    if targets &&& int AttributeTargets.Delegate <> 0 then "delegate"
+                    if targets &&& int AttributeTargets.ReturnValue <> 0 then "return value"
+                    if targets &&& int AttributeTargets.GenericParameter <> 0 then "type parameter"
+                |]
+
+            let elementTargets = attributeTargetsToString (int attrTgt)
+            let allowedTargets = attributeTargetsToString validOn
+
+            warning(InvalidAttributeTargetForLanguageElement(elementTargets, allowedTargets, mAttr))
 
     constrainedTargets
 

src/Compiler/Checking/Expressions/CheckExpressions.fsi

@@ -121,6 +121,11 @@ exception StandardOperatorRedefinitionWarning of string * range
 
 exception InvalidInternalsVisibleToAssemblyName of badName: string * fileName: string option
 
+exception InvalidAttributeTargetForLanguageElement of
+    elementTargets: string array *
+    allowedTargets: string array *
+    range: range
+
 val TcFieldInit: range -> ILFieldInit -> Const
 
 /// Indicates whether a syntactic type is allowed to include new type variables

src/Compiler/Driver/CompilerDiagnostics.fs

@@ -155,6 +155,7 @@ type Exception with
         | LibraryUseOnly m
         | FieldsFromDifferentTypes(_, _, _, m)
         | IndeterminateType m
+        | InvalidAttributeTargetForLanguageElement(_, _, m)
         | TyconBadArgs(_, _, _, m) -> Some m
 
         | FieldNotContained(_, _, _, _, _, arf, _, _) -> Some arf.Range
@@ -353,6 +354,7 @@ type Exception with
         | ConstraintSolverNullnessWarningWithTypes _ -> 3261
         | ConstraintSolverNullnessWarningWithType _ -> 3261
         | ConstraintSolverNullnessWarning _ -> 3261
+        | InvalidAttributeTargetForLanguageElement _ -> 842
         | _ -> 193
 
 type PhasedDiagnostic with
@@ -611,6 +613,9 @@ module OldStyleMessages =
     let DefinitionsInSigAndImplNotCompatibleAbbreviationsDifferE () =
         Message("DefinitionsInSigAndImplNotCompatibleAbbreviationsDiffer", "%s%s%s%s")
 
+    let InvalidAttributeTargetForLanguageElement1E () = Message("InvalidAttributeTargetForLanguageElement1", "%s%s")
+    let InvalidAttributeTargetForLanguageElement2E () = Message("InvalidAttributeTargetForLanguageElement2", "")
+
 #if DEBUG
 let mutable showParserStackOnParseError = false
 #endif
@@ -1932,6 +1937,14 @@ type Exception with
                     s2
             )
 
+        | InvalidAttributeTargetForLanguageElement(elementTargets, allowedTargets, _m) ->
+            if Array.isEmpty elementTargets then
+                os.AppendString(InvalidAttributeTargetForLanguageElement2E().Format)
+            else
+                let elementTargets = String.concat ", " elementTargets
+                let allowedTargets = allowedTargets |> String.concat ", "
+                os.AppendString(InvalidAttributeTargetForLanguageElement1E().Format elementTargets allowedTargets)
+
         // Strip TargetInvocationException wrappers
         | :? TargetInvocationException as e when isNotNull e.InnerException -> (!!e.InnerException).Output(os, suggestNames)
 

src/Compiler/FSComp.txt

@@ -698,7 +698,6 @@ tcUnnamedArgumentsDoNotFormPrefix,"The unnamed arguments do not form a prefix of
 839,tcUnexpectedConditionInImportedAssembly,"Unexpected condition in imported assembly: failed to decode AttributeUsage attribute"
 840,tcUnrecognizedAttributeTarget,"Unrecognized attribute target. Valid attribute targets are 'assembly', 'module', 'type', 'method', 'property', 'return', 'param', 'field', 'event', 'constructor'."
 841,tcAttributeIsNotValidForLanguageElementUseDo,"This attribute is not valid for use on this language element. Assembly attributes should be attached to a 'do ()' declaration, if necessary within an F# module."
-842,tcAttributeIsNotValidForLanguageElement,"This attribute is not valid for use on this language element"
 843,tcOptionalArgumentsCannotBeUsedInCustomAttribute,"Optional arguments cannot be used in custom attributes"
 844,tcPropertyCannotBeSet0,"This property cannot be set"
 845,tcPropertyOrFieldNotFoundInAttribute,"This property or field was not found on this custom attribute type"

src/Compiler/FSStrings.resx

@@ -1146,4 +1146,10 @@
   <data name="Parser.TOKEN.WHILE.BANG" xml:space="preserve">
     <value>keyword 'while!'</value>
   </data>
+  <data name="InvalidAttributeTargetForLanguageElement1" xml:space="preserve">
+    <value>This attribute cannot be applied to {0}. Valid targets are: {1}</value>
+  </data>
+  <data name="InvalidAttributeTargetForLanguageElement2" xml:space="preserve">
+    <value>This attribute is not valid for use on this language element</value>
+  </data>
 </root>