Add new rule FavourConsistentThis (#518)

Fixes #511

Author: su8898

docs/content/how-tos/rule-configuration.md

@@ -113,4 +113,5 @@ The following rules can be specified for linting.
 - [FavourTypedIgnore (FL0070)](rules/FL0070.html)
 - [CyclomaticComplexity (FL0071)](rules/FL0071.html)
 - [FailwithBadUsage (FL0072)](rules/FL0072.html)
-- [FavourReRaise (FL0073)](rules/FL0073.html)
+- [FavourReRaise (FL0073)](rules/FL0073.html)
+- [FavourConsistentThis (FL0074)](rules/FL0074.html)

docs/content/how-tos/rules/FL0074.md

@@ -0,0 +1,33 @@
+---
+title: FL0074
+category: how-to
+hide_menu: true
+---
+
+# FavourConsistentThis (FL0074)
+
+*Introduced in `0.21.1`*
+
+## Cause
+
+Rule to detect inconsistent symbol used for the instance identifier (e.g. `this`).
+
+## Rationale
+
+Using the same symbol for the instance identifier (e.g. `this`, or `self`, or `instance`) aids readability.
+
+## How To Fix
+
+Replace all occurrences of the instance symbol used with the one configured in the rule settings (e.g. if using both `self` and `this` in the same codebase, decide which one to keep, and then only use one of them, not both).
+
+## Rule Settings
+
+    {
+        "favourConsistentThis": {
+            "enabled": false,
+            "config": {
+                "symbol": "this"
+            }
+        }
+    }
+

src/FSharpLint.Core/FSharpLint.Core.fsproj

@@ -48,6 +48,7 @@
     <Compile Include="Rules\Conventions\NoPartialFunctions.fs" />
     <Compile Include="Rules\Conventions\CyclomaticComplexity.fs" />
     <Compile Include="Rules\Conventions\FavourReRaise.fs" />
+    <Compile Include="Rules\Conventions\FavourConsistentThis.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/FavourConsistentThis.fs

@@ -0,0 +1,38 @@
+module FSharpLint.Rules.FavourConsistentThis
+
+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
+
+/// Configuration of the favour consistent 'this' (FL0074) rule.
+[<RequireQualifiedAccess>]
+type Config = { Symbol: string }
+
+let runner (config: Config) args =
+    let symbol = config.Symbol
+    match args.AstNode with
+    | AstNode.Binding(SynBinding(_, _, _, _, _, _, _, pattern, _, _, range, _)) ->
+        match pattern with
+        | SynPat.LongIdent(LongIdentWithDots(identifiers, _),_, _, _, _, _) ->
+            match identifiers with
+            | head::_ when head.idText <> config.Symbol -> 
+               let error =
+                   { Range = range
+                     Message = String.Format(Resources.GetString "RulesFavourConsistentThis", config.Symbol)
+                     SuggestedFix = None
+                     TypeChecks = List.Empty }
+                   |> Array.singleton
+               error
+            | _ -> Array.empty
+        | _ -> Array.empty
+    | _ -> Array.empty
+
+let rule config =
+    { Name = "FavourConsistentThis"
+      Identifier = Identifiers.FavourConsistentThis
+      RuleConfig = { AstNodeRuleConfig.Runner = runner config; Cleanup = ignore } }
+    |> AstNodeRule

src/FSharpLint.Core/Rules/Identifiers.fs

@@ -78,3 +78,4 @@ let FavourTypedIgnore = identifier 70
 let CyclomaticComplexity = identifier 71
 let FailwithBadUsage = identifier 72
 let FavourReRaise = identifier 73
+let FavourConsistentThis = identifier 74

src/FSharpLint.Core/Text.resx

@@ -330,4 +330,7 @@
   <data name="RulesFavourReRaise" xml:space="preserve">
     <value>Rather use reraise() instead of using raise with the same captured exception.</value>
   </data>
+  <data name="RulesFavourConsistentThis" xml:space="preserve">
+    <value>Prefer using '{0}' consistently.</value>
+  </data>
 </root>

src/FSharpLint.Core/fsharplint.json

@@ -266,6 +266,12 @@
     "tupleOfWildcards": { "enabled": true },
     "favourTypedIgnore": { "enabled": false },
     "favourReRaise": { "enabled": true },
+    "favourConsistentThis": {
+        "enabled": false,
+        "config": {
+            "symbol": "this"
+        }
+    },
     "indentation": {
         "enabled": false
     },

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

@@ -36,6 +36,7 @@
     <Compile Include="Rules\Conventions\SourceLength.fs" />
     <Compile Include="Rules\Conventions\NoPartialFunctions.fs" />
     <Compile Include="Rules\Conventions\FavourReRaise.fs" />
+    <Compile Include="Rules\Conventions\FavourConsistentThis.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/FavourConsistentThis.fs

@@ -0,0 +1,59 @@
+module FSharpLint.Core.Tests.Rules.Conventions.FavourConsistentThis
+
+open NUnit.Framework
+open FSharpLint.Rules
+open System
+
+[<TestFixture>]
+type TestConventionsFavourConsistentThis() =
+    inherit TestAstNodeRuleBase.TestAstNodeRuleBase(FavourConsistentThis.rule { Symbol = "this" })
+
+    [<Test>]
+    member this.ConsistentThisShouldNotProduceError() =
+        this.Parse """
+type Foo =
+    { Bar : Baz }
+    member this.FooBar = 
+        ()
+    member this.FooBarBaz x =
+        failwith "foobarbaz" """
+
+        Assert.IsTrue this.NoErrorsExist
+
+    [<Test>]
+    member this.InConsistentSelfShouldProduceError() =
+        this.Parse """
+type Foo =
+    { Bar : Baz }
+    member self.FooBar = 
+        ()
+    member this.FooBarBaz x =
+        failwith "foobarbaz" """
+
+        Assert.IsTrue this.ErrorsExist
+        Assert.IsTrue(this.ErrorExistsAt(4, 11))
+
+    [<Test>]
+    member this.InConsistentSelfShouldProduceError_2() =
+        this.Parse """
+type Foo =
+    { Bar : Baz }
+    member this.FooBar = 
+        ()
+    member self.FooBarBaz x =
+        failwith "foobarbaz" """
+
+        Assert.IsTrue this.ErrorsExist
+        Assert.IsTrue(this.ErrorExistsAt(6, 11))
+
+    [<Test>]
+    member this.InConsistentSelfShouldProduceError_3() =
+        this.Parse """
+type CustomerName(firstName, middleInitial, lastName) =
+    member this.FirstName = firstName
+    member self.MiddleInitial = middleInitial
+    member this.LastName = lastName """
+
+        Assert.IsTrue this.ErrorsExist
+        Assert.IsTrue(this.ErrorExistsAt(4, 11))
+