Merge pull request #85 from nojaf/good-stuff

Add analyzers from FSharp.Formatting PR

Author: nojaf

CHANGELOG.md

@@ -1,5 +1,15 @@
 # Changelog
 
+## 0.10.0 - 2024-03-29
+
+### Added
+* HeadConsEmptyListPatternAnalyzer. [#85](https://github.com/ionide/ionide-analyzers/pull/85)
+* ListEqualsEmptyListAnalyzer. [#85](https://github.com/ionide/ionide-analyzers/pull/85)
+* ReturnStructPartialActivePatternAnalyzer [#85](https://github.com/ionide/ionide-analyzers/pull/85)
+* CombinePipedModuleFunctionsAnalyzer [#85](https://github.com/ionide/ionide-analyzers/pull/85)
+* EqualsNullAnalyzer [#85](https://github.com/ionide/ionide-analyzers/pull/85)
+* StructDiscriminatedUnionAnalyzer. [#85](https://github.com/ionide/ionide-analyzers/pull/85)
+
 ## 0.9.0 - 2024-02-15
 
 ### Changed

build.fsx

@@ -364,9 +364,11 @@ pipeline "NewAnalyzer" {
             let analyzerContent =
                 $"""module Ionide.Analyzers.%s{category}.%s{analyzerName}
 
+open System.Collections.Generic
 open FSharp.Compiler.Symbols
 open FSharp.Compiler.Text
 open FSharp.Compiler.Syntax
+open FSharp.Compiler.SyntaxTrivia
 open FSharp.Analyzers.SDK
 open FSharp.Analyzers.SDK.ASTCollecting
 open FSharp.Analyzers.SDK.TASTCollecting

docs/img/EqualsNullAnalyzer.gif

@@ -0,0 +1,30 @@
+---
+title: ListEqualsEmptyListAnalyzer
+category: performance
+categoryindex: 4
+index: 1
+---
+
+# ListEqualsEmptyListAnalyzer
+
+## Problem
+
+It is less performant to check if a list is empty by using the `=` operator.
+
+```fsharp
+let a = [ 1; 2; 3 ]
+// Analyzer will trigger
+let b = [] = a
+```
+
+## Fix
+
+```fsharp
+let b = List.isEmpty a // will check if there is no tail which is faster than the equality check.
+```
+
+## Code fix
+
+This analyzer has a code fix for Ionide:
+
+![Code fix for ListEqualsEmptyList](../img/ListEqualsEmptyListAnalyzer.gif)

docs/img/HeadConsEmptyListPatternAnalyzer.gif

@@ -0,0 +1,37 @@
+---
+title: ReturnStructPartialActivePatternAnalyzer
+category: performance
+categoryindex: 4
+index: 2
+---
+
+# ReturnStructPartialActivePatternAnalyzer
+
+## Problem
+
+Since F# 6.0 you can use [struct representations for partial active patterns](https://learn.microsoft.com/en-us/dotnet/fsharp/whats-new/fsharp-6#struct-representations-for-partial-active-patterns).  
+The net result is that allocations are reduced. Whether you really want this will depend on your own code.
+
+```fsharp
+// Analyzer will trigger.
+let (|Int|_|) str =
+   match System.Int32.TryParse(str) with
+   | true, int -> Some(int)
+   | _ -> None
+```
+
+## Fix
+
+```fsharp
+[<return: Struct>]
+let (|Int|_|) str =
+   match System.Int32.TryParse(str) with
+   | true, int -> ValueSome(int)
+   | _ -> ValueNone
+```
+
+## Code fix
+
+This analyzer has a code fix for Ionide:
+
+![code fix for ReturnStructPartialActivePattern](../img/ReturnStructPartialActivePatternAnalyzer.gif)

docs/img/ListEqualsEmptyListAnalyzer.gif

@@ -0,0 +1,27 @@
+---
+title: CombinePipedModuleFunctionsAnalyzer
+category: performance
+categoryindex: 4
+index: 3
+---
+
+# CombinePipedModuleFunctionsAnalyzer
+
+## Problem
+
+Subsequent collection functions like `List.filter` and `List.map` can sometimes be combined into `List.choose`.
+
+```fsharp
+let a b =
+    b
+    |> List.filter (fun x -> x < 20)
+    |> List.map (fun y -> y * 2)
+```
+
+## Fix
+
+```fsharp
+let a b =
+    b
+    |> List.choose (fun x -> if x < 20 then Some(x * 2) else None)
+```