Fix CI cancellation issues

Author: TheAngryByrd

build/build.fs

@@ -13,11 +13,30 @@ open System.IO
 open Fake.BuildServer
 open FsToolkit.Build
 
+let environVarAsBoolOrDefault varName defaultValue =
+    let truthyConsts = [
+        "1"
+        "Y"
+        "YES"
+        "T"
+        "TRUE"
+    ]
+
+    try
+        let envvar = (Environment.environVar varName).ToUpper()
+
+        truthyConsts
+        |> List.exists ((=) envvar)
+    with _ ->
+        defaultValue
+
 let project = "FsToolkit.ErrorHandling"
 
 let summary =
     "FsToolkit.ErrorHandling is a utility library to work with the Result type in F#, and allows you to do clear, simple and powerful error handling."
 
+let isCI = lazy (environVarAsBoolOrDefault "CI" false)
+
 let isRelease (targets: Target list) =
     targets
     |> Seq.map (fun t -> t.Name)
@@ -93,6 +112,18 @@ let failOnBadExitAndPrint (p: ProcessResult) =
 
         failwithf "failed with exitcode %d" p.ExitCode
 
+// github actions are terrible and will cancel runner operations if using too much CPU
+// https://github.com/actions/runner-images/discussions/7188#discussioncomment-6672934
+let maxCpuCount = lazy (if isCI.Value then Some(Some 2) else None)
+
+/// MaxCpu not used on unix https://github.com/fsprojects/FAKE/blob/82e38df01e4b31e5daa3623abff57e6462430395/src/app/Fake.DotNet.MSBuild/MSBuild.fs#L858-L861
+let maxCpuMsBuild =
+    lazy
+        (match maxCpuCount.Value with
+         | None -> ""
+         | Some None -> "/m"
+         | Some(Some x) -> $"/m:%d{x}")
+
 module dotnet =
     let watch cmdParam program args =
         DotNet.exec cmdParam (sprintf "watch %s" program) args
@@ -144,10 +175,16 @@ let clean _ =
 
 
 let build ctx =
-    let setParams (defaults: DotNet.BuildOptions) = {
-        defaults with
+
+    let args = [ maxCpuMsBuild.Value ]
+
+    let setParams (c: DotNet.BuildOptions) = {
+        c with
             NoRestore = true
             Configuration = (configuration ctx.Context.AllExecutingTargets)
+            Common =
+                c.Common
+                |> DotNet.Options.withAdditionalArgs args
     }
 
     DotNet.build setParams solutionFile
@@ -166,7 +203,10 @@ let npmRestore _ = Npm.install id
 
 let dotnetTest ctx =
 
-    let args = [ "--no-build" ]
+    let args = [
+        "--no-build"
+        maxCpuMsBuild.Value
+    ]
 
     DotNet.test
         (fun c ->