Add new rule FriendlyAsyncOverload

Fixes fsprojects#517

src/FSharpLint.Core/FSharpLint.Core.fsproj

@@ -47,6 +47,7 @@
     <Compile Include="Rules\Conventions\NestedStatements.fs" />
     <Compile Include="Rules\Conventions\NoPartialFunctions.fs" />
     <Compile Include="Rules\Conventions\CyclomaticComplexity.fs" />
+    <Compile Include="Rules\Conventions\FriendlyAsyncOverload.fs" />
     <Compile Include="Rules\Conventions\RaiseWithTooManyArguments\RaiseWithTooManyArgumentsHelper.fs" />
     <Compile Include="Rules\Conventions\RaiseWithTooManyArguments\FailwithWithSingleArgument.fs" />
     <Compile Include="Rules\Conventions\RaiseWithTooManyArguments\RaiseWithSingleArgument.fs" />

src/FSharpLint.Core/Rules/Conventions/FriendlyAsyncOverload.fs

@@ -0,0 +1,71 @@
+module FSharpLint.Rules.FriendlyAsyncOverload
+
+open FSharpLint.Framework
+open FSharpLint.Framework.Suggestion
+open FSharp.Compiler.Syntax
+open FSharp.Compiler.Text
+open FSharpLint.Framework.Ast
+open FSharpLint.Framework.Rules
+open System
+
+type NodeDetails = { Ident: string; Range: range }
+
+let rec private getIdentFromSynPat =
+    function
+    | SynPat.LongIdent (longDotId = longDotId) ->
+        longDotId
+        |> ExpressionUtilities.longIdentWithDotsToString
+        |> Some
+    | SynPat.Typed (pat, _, _) -> getIdentFromSynPat pat
+    | _ -> None
+
+let runner (args: AstNodeRuleParams) =
+    let hasAsync (syntaxArray: AbstractSyntaxArray.Node []) nodeIndex fnIdent =
+        let rec hasAsync index =
+            if index >= syntaxArray.Length then
+                None
+            else
+                let node = syntaxArray.[index].Actual
+                match node with
+                | AstNode.Binding (SynBinding (_, _, _, _, _attributes, _, _, pattern, _, _, range, _)) ->
+                    match getIdentFromSynPat pattern with
+                    | Some ident when ident = fnIdent + "Async" ->
+                        Some(
+                            { Ident = fnIdent
+                              Range = range }
+                        )
+                    | _ -> hasAsync (index + 1)
+                | _ -> hasAsync (index + 1)
+
+        hasAsync nodeIndex
+
+    match args.AstNode with
+    | AstNode.Binding (SynBinding (_, _, _, _, _, _, _, pattern, synInfo, _, range, _)) ->
+        match synInfo with
+        | Some (SynBindingReturnInfo ((SynType.App(SynType.LongIdent(LongIdentWithDots(ident,_)),_,_,_,_,_,_)),_,_)) ->
+            match ident with
+            | head::_ when head.idText = "Async" ->
+                let idents = getIdentFromSynPat pattern
+                match idents with
+                | Some ident when ident.EndsWith("Async") = false ->
+                    match hasAsync args.SyntaxArray args.NodeIndex ident with
+                    | Some nod -> Array.empty
+                    | None ->
+                        { Range = range
+                          Message = String.Format(Resources.GetString "RulesFriendlyAsyncOverload", ident)
+                          SuggestedFix = None
+                          TypeChecks = [] }
+                        |> Array.singleton
+                | _ -> Array.empty
+            | _ -> Array.empty
+        | _ -> Array.empty
+    | _ -> Array.empty
+
+
+let rule =
+    { Name = "FriendlyAsyncOverload"
+      Identifier = Identifiers.FriendlyAsyncOverload
+      RuleConfig =
+        { AstNodeRuleConfig.Runner = runner
+          Cleanup = ignore } }
+    |> AstNodeRule

src/FSharpLint.Core/Rules/Identifiers.fs

@@ -77,3 +77,4 @@ let GenericTypesNames = identifier 69
 let FavourTypedIgnore = identifier 70
 let CyclomaticComplexity = identifier 71
 let FailwithBadUsage = identifier 72
+let FriendlyAsyncOverload = identifier 77

src/FSharpLint.Core/Text.resx

@@ -327,4 +327,7 @@
   <data name="RulesFailwithBadUsage" xml:space="preserve">
     <value>Bad usage of failwith: {0}.</value>
   </data>
+  <data name="RulesFriendlyAsyncOverload" xml:space="preserve">
+    <value>Consider using a friendly async overload for {0}.</value>
+  </data>
 </root>

src/FSharpLint.Core/fsharplint.json

@@ -45,6 +45,7 @@
     "invalidArgWithTwoArguments": { "enabled": true },
     "failwithfWithArgumentsMatchingFormatString": { "enabled": true },
     "failwithBadUsage": { "enabled": true },
+    "friendlyAsyncOverload": { "enabled": true },
     "maxLinesInLambdaFunction": {
         "enabled": false,
         "config": {

tests/FSharpLint.Core.Tests/FSharpLint.Core.Tests.fsproj

@@ -35,6 +35,7 @@
     <Compile Include="Rules\Conventions\FunctionReimplementation.fs" />
     <Compile Include="Rules\Conventions\SourceLength.fs" />
     <Compile Include="Rules\Conventions\NoPartialFunctions.fs" />
+    <Compile Include="Rules\Conventions\FriendlyAsyncOverload.fs" />
     <Compile Include="Rules\Conventions\Naming\NamingHelpers.fs" />
     <Compile Include="Rules\Conventions\Naming\InterfaceNames.fs" />
     <Compile Include="Rules\Conventions\Naming\ExceptionNames.fs" />

tests/FSharpLint.Core.Tests/Rules/Conventions/FriendlyAsyncOverload.fs

@@ -0,0 +1,37 @@
+module FSharpLint.Core.Tests.Rules.Conventions.FriendlyAsyncOverload
+
+open NUnit.Framework
+open FSharpLint.Rules
+
+[<TestFixture>]
+type TestConventionsFriendlyAsyncOverload() =
+    inherit TestAstNodeRuleBase.TestAstNodeRuleBase(FriendlyAsyncOverload.rule)
+
+    [<Test>]
+    member this.``async function must suggest friendly implementation``() = 
+        this.Parse("""
+module Foo =
+    let Bar(): Async<unit> =
+        Async.Sleep 5""")
+
+        Assert.IsTrue(this.ErrorExistsAt(3, 8))
+
+    [<Test>]
+    member this.``async function with friendly implementation must not have errors``() =
+        this.Parse("""
+module Foo =
+let Bar(): Async<unit> =
+    Async.Sleep 5
+let BarAsync(): Task<unit> =
+    Bar() |> Async.StartAsTask""")
+
+        this.AssertNoWarnings()
+
+    [<Test>]
+    member this.``non async function must not create warnings``() =
+        this.Parse("""
+module Foo =
+    let Bar() =
+        ()""")
+
+        this.AssertNoWarnings()