Tail recursion warning and attribute, analysis after optimization (#15503)

* Add TailCall attribute
Move work of Avi Avni to current sources but use a field in cenv instead of a function parameter to pass around

* Adjust error number after merge

* add two test cases for type members

* Don't try to split empty CurriedArgInfos

* Add more member tests

* seems like we need to build up the env.mustTailCall set earlier in the traversal to have the content ready when checking members which call each other

* Fix an error from migrating the old PR to current sources.

* As cenv is mutated in loops, doing "with" copies isn't that great as the failing CI shows.
Making isTailCall also mutable is error prone as one has to switch back to orig values in many places.
So refactor to use a flag like Avi did.
This should fix the side effects (shown by the failing CI) and more tailrec specific tests

* update baselines for FSharp.Core to include TailCallAttribute

* warn for rec call in binding, still very WIP

* - improve check for problematic bindings to tailcall attributed functions
- add tests

* improve seq support

* add language version flag

* improve tests a bit

* add tests for async expressions

* add tests for module rec

* Improve handling of ModuleOrNamespaceContents.TMDefDo and extend testing

* suppress some invalid warnings by keeping track of ranges that are annotated with [<TailRec>]

* fix build

* use Stamp instead of LogicalName as the Map key

* fix error number after merge

* remove TailCall check code from PostInferenceChecks.fs

* Add new file TailCallChecks.fs to focus on tail call checks

* first steps to remove limits calculations

* remove last bits of limits

* don't bother with attribute checking here

* remove more unneeded code

* small optimization

* Adjust error number after main merge

* add TailCallChecks.fs to .fantomasignore

* remove last non-tailrec error reporting from dedicated file

* - add fsi file
- trim down some more

* simplify

* Remove resumable checks

* remove external handling

* remove isInAppExpr

* remove returnScope

* remove boundTyparNames

* remove argVals from env

* let's drop quote and reflect, too, for now

* remove usesQuotations

* get rid of range-based approach, collect TailRec-attributed bindings upfront and just traverse these

* fold instead of mutate

* format

* make tests more challenging

* do the TailCall checks during the main traversal

* WIP: move TailCallChecks into main3 after optimization

* format

* let TailCallChecks.fs be formatted

* bring over support for TyLambda bodies from other branch

* adjust expected errors

* fix the doubled error messages

* fix seq analysis

* cleanup

* cover some more rec constructs

* remove commented code from tests

* Rename the type "IsTailCall" to "TailCall"

* model boolean as dedicated type "TailCallReturnType"

* remove unused members of type "PermitByRefExpr"

* remove unused mustTailCallExprs from env

* add comment to explain origin of PermitByRefExpr

* First stab at support for continuation-passing-style

* - refactor approach for CPS support to be much simpler
- more CPS tests

* one env ought to be enough for everyone

* report time for "TailCall Checks"

* clean up unused function args

* improve some comments and names

* add API docs for TailCall attribute

* add xml comment for TailCallChecks.CheckImplFile

* Update src/FSharp.Core/prim-types.fsi

Co-authored-by: Petr <[email protected]>

* remove some superfluous stuff from CheckLambdas

* More detailed comment

* extend test with an inner class type

* optimize

* update xlf

* adjust error messages after xlf update

* revert white space changes that sneaked in during rebase

---------

Co-authored-by: Petr <[email protected]>

Author: dawedawe

src/Compiler/Checking/TailCallChecks.fs

@@ -0,0 +1,13 @@
+module internal FSharp.Compiler.TailCallChecks
+
+open FSharp.Compiler
+open FSharp.Compiler.TcGlobals
+open FSharp.Compiler.TypedTree
+
+/// Perform the TailCall analysis on the optimized TAST for a file.
+/// The TAST is traversed analogously to the PostInferenceChecks phase.
+/// For functions that are annotated with the [<TailCall>] attribute, a warning is emmitted if they are called in a
+/// non-tailrecursive manner in the recursive scope of the function.
+/// The ModuleOrNamespaceContents aren't mutated in any way by performing this check.
+val CheckImplFile:
+    g: TcGlobals * amap: Import.ImportMap * reportErrors: bool * implFileContents: ModuleOrNamespaceContents -> unit

src/Compiler/Checking/TailCallChecks.fsi

@@ -40,6 +40,7 @@ open FSharp.Compiler.CreateILModule
 open FSharp.Compiler.DependencyManager
 open FSharp.Compiler.Diagnostics
 open FSharp.Compiler.DiagnosticsLogger
+open FSharp.Compiler.Features
 open FSharp.Compiler.IlxGen
 open FSharp.Compiler.InfoReader
 open FSharp.Compiler.IO
@@ -878,6 +879,14 @@ let main3
 
         optimizedImpls, EncodeOptimizationData(tcGlobals, tcConfig, outfile, exportRemapping, (generatedCcu, optimizationData), false)
 
+    if tcGlobals.langVersion.SupportsFeature LanguageFeature.WarningWhenTailRecAttributeButNonTailRecUsage then
+        match optimizedImpls with
+        | CheckedAssemblyAfterOptimization checkedImplFileAfterOptimizations ->
+            ReportTime tcConfig ("TailCall Checks")
+
+            for f in checkedImplFileAfterOptimizations do
+                TailCallChecks.CheckImplFile(tcGlobals, tcImports.GetImportMap(), true, f.ImplFile.Contents)
+
     let refAssemblySignatureHash =
         match tcConfig.emitMetadataAssembly with
         | MetadataAssemblyGeneration.None -> None

src/Compiler/Driver/fsc.fs

@@ -1576,6 +1576,7 @@ featureExtendedStringInterpolation,"Extended string interpolation similar to C#
 featureWarningWhenMultipleRecdTypeChoice,"Raises warnings when multiple record type matches were found during name resolution because of overlapping field names."
 featureImprovedImpliedArgumentNames,"Improved implied argument names"
 featureStrictIndentation,"Raises errors on incorrect indentation, allows better recovery and analysis during editing"
+featureChkNotTailRecursive,"Raises warnings if a member or function has the 'TailCall' attribute, but is not being used in a tail recursive way."
 3353,fsiInvalidDirective,"Invalid directive '#%s %s'"
 3354,tcNotAFunctionButIndexerNamedIndexingNotYetEnabled,"This value supports indexing, e.g. '%s.[index]'. The syntax '%s[index]' requires /langversion:preview. See https://aka.ms/fsharp-index-notation."
 3354,tcNotAFunctionButIndexerIndexingNotYetEnabled,"This expression supports indexing, e.g. 'expr.[index]'. The syntax 'expr[index]' requires /langversion:preview. See https://aka.ms/fsharp-index-notation."
@@ -1700,4 +1701,5 @@ featureInformationalObjInferenceDiagnostic,"Diagnostic 3559 (warn when obj infer
 3566,tcMultipleRecdTypeChoice,"Multiple type matches were found:\n%s\nThe type '%s' was used. Due to the overlapping field names\n%s\nconsider using type annotations or change the order of open statements."
 3567,parsMissingMemberBody,"Expecting member body"
 3568,parsMissingKeyword,"Missing keyword '%s'"
+3569,chkNotTailRecursive,"The member or function '%s' has the 'TailCallAttribute' attribute, but is not being used in a tail recursive way."
 3577,tcOverrideUsesMultipleArgumentsInsteadOfTuple,"This override takes a tuple instead of multiple arguments. Try to add an additional layer of parentheses at the method definition (e.g. 'member _.Foo((x, y))'), or remove parentheses at the abstract method declaration (e.g. 'abstract member Foo: 'a * 'b -> 'c')."

src/Compiler/FSComp.txt

@@ -337,6 +337,8 @@
     <Compile Include="Checking\QuotationTranslator.fs" />
     <Compile Include="Checking\PostInferenceChecks.fsi" />
     <Compile Include="Checking\PostInferenceChecks.fs" />
+    <Compile Include="Checking\TailCallChecks.fsi" />
+    <Compile Include="Checking\TailCallChecks.fs" />
     <Compile Include="Checking\CheckBasics.fsi" />
     <Compile Include="Checking\CheckBasics.fs" />
     <Compile Include="Checking\CheckRecordSyntaxHelpers.fsi" />

src/Compiler/FSharp.Compiler.Service.fsproj

@@ -71,6 +71,7 @@ type LanguageFeature =
     | WarningWhenMultipleRecdTypeChoice
     | ImprovedImpliedArgumentNames
     | DiagnosticForObjInference
+    | WarningWhenTailRecAttributeButNonTailRecUsage
 
 /// LanguageVersion management
 type LanguageVersion(versionText) =
@@ -165,6 +166,7 @@ type LanguageVersion(versionText) =
                 LanguageFeature.ImprovedImpliedArgumentNames, previewVersion
                 LanguageFeature.DiagnosticForObjInference, previewVersion
                 LanguageFeature.StrictIndentation, previewVersion
+                LanguageFeature.WarningWhenTailRecAttributeButNonTailRecUsage, previewVersion
 
             ]
 
@@ -291,6 +293,7 @@ type LanguageVersion(versionText) =
         | LanguageFeature.ImprovedImpliedArgumentNames -> FSComp.SR.featureImprovedImpliedArgumentNames ()
         | LanguageFeature.DiagnosticForObjInference -> FSComp.SR.featureInformationalObjInferenceDiagnostic ()
         | LanguageFeature.StrictIndentation -> FSComp.SR.featureStrictIndentation ()
+        | LanguageFeature.WarningWhenTailRecAttributeButNonTailRecUsage -> FSComp.SR.featureChkNotTailRecursive ()
 
     /// Get a version string associated with the given feature.
     static member GetFeatureVersionString feature =

src/Compiler/Facilities/LanguageFeatures.fs

@@ -61,6 +61,7 @@ type LanguageFeature =
     | WarningWhenMultipleRecdTypeChoice
     | ImprovedImpliedArgumentNames
     | DiagnosticForObjInference
+    | WarningWhenTailRecAttributeButNonTailRecUsage
 
 /// LanguageVersion management
 type LanguageVersion =

src/Compiler/Facilities/LanguageFeatures.fsi

@@ -1509,6 +1509,7 @@ type TcGlobals(
   member val attrib_CompilerFeatureRequiredAttribute       = findSysAttrib "System.Runtime.CompilerServices.CompilerFeatureRequiredAttribute"
   member val attrib_SetsRequiredMembersAttribute           = findSysAttrib "System.Diagnostics.CodeAnalysis.SetsRequiredMembersAttribute"
   member val attrib_RequiredMemberAttribute                = findSysAttrib "System.Runtime.CompilerServices.RequiredMemberAttribute"
+  member val attrib_TailCallAttribute                      = mk_MFCore_attrib "TailCallAttribute"
 
   member g.improveType tcref tinst = improveTy tcref tinst