Warn if unused top-level function is not included is signature file. (#14567)

* Warn is unused toplevel function is not included is signature file.

* Add HasSignature to Val and Symbol.fs

* Verify the parent of the value has a signature file.

* Scope warning to let bindings only.

* Apply feedback from code review.

* Surface Area Release mode

* Add test for type extension.

Author: nojaf

src/Compiler/Checking/PostInferenceChecks.fs

@@ -302,12 +302,24 @@ let BindVal cenv env (v: Val) =
     //printfn "binding %s..." v.DisplayName
     let alreadyDone = cenv.boundVals.ContainsKey v.Stamp
     cenv.boundVals[v.Stamp] <- 1
+    
+    let topLevelBindingHiddenBySignatureFile () =
+        let parentHasSignatureFile () =
+            match v.TryDeclaringEntity with
+            | ParentNone -> false
+            | Parent p ->
+                match p.TryDeref with
+                | ValueNone -> false
+                | ValueSome e -> e.HasSignatureFile
+
+        v.IsModuleBinding && not v.HasSignatureFile && parentHasSignatureFile ()
+    
     if not env.external &&
        not alreadyDone &&
        cenv.reportErrors && 
        not v.HasBeenReferenced && 
-       not v.IsCompiledAsTopLevel && 
-       not (v.DisplayName.StartsWithOrdinal("_")) && 
+       (not v.IsCompiledAsTopLevel || topLevelBindingHiddenBySignatureFile ()) &&
+       not (v.DisplayName.StartsWithOrdinal("_")) &&
        not v.IsCompilerGenerated then 
 
         if v.IsCtorThisVal then

src/Compiler/Service/FSharpCheckerResults.fs

@@ -270,9 +270,7 @@ type FSharpSymbolUse(denv: DisplayEnv, symbol: FSharpSymbol, inst: TyparInstanti
 
                 let fileHasSignatureFile = fileSignatureLocation <> fileDeclarationLocation
 
-                let symbolIsNotInSignatureFile = m.SignatureLocation = Some m.DeclarationLocation
-
-                fileHasSignatureFile && symbolIsNotInSignatureFile
+                fileHasSignatureFile && not m.HasSignatureFile
                 || not m.IsModuleValueOrMember
                 || m.Accessibility.IsPrivate
             | :? FSharpEntity as m -> m.Accessibility.IsPrivate

src/Compiler/Symbols/Symbols.fs

@@ -1826,6 +1826,14 @@ type FSharpMemberOrFunctionOrValue(cenv, d:FSharpMemberOrValData, item) =
         | P _ -> true
         | _ -> false
 
+    member x.HasSignatureFile =
+        match fsharpInfo() with
+        | None -> false
+        | Some vref ->
+            match vref.TryDeref with
+            | ValueNone -> false
+            | ValueSome v -> v.HasSignatureFile
+    
     member _.IsEvent = 
         match d with 
         | E _ -> true

src/Compiler/Symbols/Symbols.fsi

@@ -816,6 +816,9 @@ type FSharpMemberOrFunctionOrValue =
     /// Indicates if this is a method member
     member IsMethod: bool
 
+    /// Indicates if the value has a signature file counterpart
+    member HasSignatureFile: bool
+
     /// Indicates if this is a property and there exists an associated getter method
     member HasGetterMethod: bool
 

src/Compiler/TypedTree/TypedTree.fs

@@ -1276,6 +1276,8 @@ type Entity =
 
     /// Indicates if we have pre-determined that a type definition has a self-referential constructor using 'as x'
     member x.HasSelfReferentialConstructor = x.entity_flags.HasSelfReferentialConstructor
+    
+    member x.HasSignatureFile = x.SigRange <> x.DefinitionRange
 
     /// Set the custom attributes on an F# type definition.
     member x.SetAttribs attribs = x.entity_attribs <- attribs
@@ -2803,6 +2805,9 @@ type Val =
     //  Indicates if this value was declared to be a type function, e.g. "let f<'a> = typeof<'a>"
     member x.IsTypeFunction = x.val_flags.IsTypeFunction
 
+    member x.HasSignatureFile =
+        x.SigRange <> x.DefinitionRange
+    
     /// Get the inline declaration on the value
     member x.InlineInfo = x.val_flags.InlineInfo
 

src/Compiler/TypedTree/TypedTree.fsi

@@ -571,6 +571,9 @@ type Entity =
     /// Indicates if we have pre-determined that a type definition has a self-referential constructor using 'as x'
     member HasSelfReferentialConstructor: bool
 
+    /// Indicates if the value has a signature file counterpart
+    member HasSignatureFile: bool
+
     /// Get the Abstract IL scope, nesting type metadata for this
     /// type definition, assuming it is backed by Abstract IL metadata.
     member ILTyconInfo: TILObjectReprData
@@ -2085,6 +2088,9 @@ type Val =
 
     member IsTypeFunction: bool
 
+    /// Indicates if the value has a signature file counterpart
+    member HasSignatureFile: bool
+
     /// The value of a value or member marked with [<LiteralAttribute>]
     member LiteralValue: Const option
 

tests/FSharp.Compiler.ComponentTests/CompilerOptions/fsc/warnon/warnon.fs

@@ -34,3 +34,111 @@ module warnon =
         |> withDiagnosticMessageMatches "The value 'n' is unused$"
         |> ignore
 
+    [<Fact>]
+    let ``warnon unused public function hidden by signature file`` () =
+        let signatureFile: SourceCodeFileKind =
+            SourceCodeFileKind.Create(
+                "Library.fsi",
+                """
+module Foo
+
+val add: a:int -> b:int -> int
+    """     )
+
+        let implementationFile =
+            SourceCodeFileKind.Create(
+                "Library.fs",
+                """
+module Foo
+
+let add a b = a + b
+let subtract a b = a - b
+    """         )
+
+        fsFromString signatureFile
+        |> FS
+        |> withAdditionalSourceFile implementationFile
+        |> withOptions ["--warnon:FS1182"]
+        |> asLibrary
+        |> compile
+        |> withWarningCode 1182
+        |> withDiagnosticMessageMatches "The value 'subtract' is unused$"
+        |> ignore
+
+    [<Fact>]
+    let ``Don't warnon unused public function`` () =
+        let implementationFile =
+            SourceCodeFileKind.Create(
+                "Library.fs",
+                """
+module Foo
+
+let add a b = a + b
+let subtract a b = a - b
+    """         )
+
+        fsFromString implementationFile
+        |> FS
+        |> withOptions ["--warnon:FS1182"]
+        |> asLibrary
+        |> compile
+        |> withDiagnostics []
+        |> ignore
+
+    [<Fact>]
+    let ``Don't warnon unused public function hidden by signature file that starts with an underscore`` () =
+        let signatureFile: SourceCodeFileKind =
+            SourceCodeFileKind.Create(
+                "Library.fsi",
+                """
+module Foo
+
+val add: a:int -> b:int -> int
+    """     )
+
+        let implementationFile =
+            SourceCodeFileKind.Create(
+                "Library.fs",
+                """
+module Foo
+
+let add a b = a + b
+let _subtract a b = a - b
+    """         )
+
+        fsFromString signatureFile
+        |> FS
+        |> withAdditionalSourceFile implementationFile
+        |> withOptions ["--warnon:FS1182"]
+        |> asLibrary
+        |> compile
+        |> withDiagnostics []
+        |> ignore
+
+    [<Fact>]
+    let ``Type extensions are not included in this warnon check`` () =
+        let signatureFile: SourceCodeFileKind =
+            SourceCodeFileKind.Create(
+                "Library.fsi",
+                """
+module Foo
+    """     )
+
+        let implementationFile =
+            SourceCodeFileKind.Create(
+                "Library.fs",
+                """
+module Foo
+
+type System.Int32 with
+    member x.Bar () = x + 1
+    """         )
+
+        fsFromString signatureFile
+        |> FS
+        |> withAdditionalSourceFile implementationFile
+        |> withOptions ["--warnon:FS1182"]
+        |> asLibrary
+        |> compile
+        |> shouldSucceed
+        |> ignore

tests/FSharp.Compiler.Service.Tests/FSharp.Compiler.Service.SurfaceArea.netstandard20.debug.bsl

@@ -2012,7 +2012,6 @@ FSharp.Compiler.CodeAnalysis.FSharpCheckProjectResults: FSharp.Compiler.Symbols.
 FSharp.Compiler.CodeAnalysis.FSharpCheckProjectResults: System.String ToString()
 FSharp.Compiler.CodeAnalysis.FSharpCheckProjectResults: System.String[] DependencyFiles
 FSharp.Compiler.CodeAnalysis.FSharpCheckProjectResults: System.String[] get_DependencyFiles()
-FSharp.Compiler.CodeAnalysis.FSharpChecker
 FSharp.Compiler.CodeAnalysis.FSharpChecker: FSharp.Compiler.CodeAnalysis.FSharpChecker Create(Microsoft.FSharp.Core.FSharpOption`1[System.Int32], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.CodeAnalysis.LegacyReferenceResolver], Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Core.FSharpFunc`2[System.Tuple`2[System.String,System.DateTime],Microsoft.FSharp.Core.FSharpOption`1[System.Tuple`3[System.Object,System.IntPtr,System.Int32]]]], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean])
 FSharp.Compiler.CodeAnalysis.FSharpChecker: FSharp.Compiler.CodeAnalysis.FSharpChecker Instance
 FSharp.Compiler.CodeAnalysis.FSharpChecker: FSharp.Compiler.CodeAnalysis.FSharpChecker get_Instance()
@@ -4782,6 +4781,7 @@ FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean Equals(System.Obj
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean EventIsStandard
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean HasGetterMethod
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean HasSetterMethod
+FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean HasSignatureFile
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean IsActivePattern
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean IsBaseValue
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean IsCompilerGenerated
@@ -4814,6 +4814,7 @@ FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean IsValue
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_EventIsStandard()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_HasGetterMethod()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_HasSetterMethod()
+FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_HasSignatureFile()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_IsActivePattern()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_IsBaseValue()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_IsCompilerGenerated()

tests/FSharp.Compiler.Service.Tests/FSharp.Compiler.Service.SurfaceArea.netstandard20.release.bsl

@@ -4781,6 +4781,7 @@ FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean Equals(System.Obj
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean EventIsStandard
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean HasGetterMethod
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean HasSetterMethod
+FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean HasSignatureFile
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean IsActivePattern
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean IsBaseValue
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean IsCompilerGenerated
@@ -4813,6 +4814,7 @@ FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean IsValue
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_EventIsStandard()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_HasGetterMethod()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_HasSetterMethod()
+FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_HasSignatureFile()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_IsActivePattern()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_IsBaseValue()
 FSharp.Compiler.Symbols.FSharpMemberOrFunctionOrValue: Boolean get_IsCompilerGenerated()