Add LanguageFeature

Author: edgarfgp

src/Compiler/Checking/Expressions/CheckComputationExpressions.fs

@@ -1793,6 +1793,9 @@ let rec TryTranslateComputationExpression
                 let supportsUseBangBindingValueDiscard =
                     ceenv.cenv.g.langVersion.SupportsFeature LanguageFeature.UseBangBindingValueDiscard
 
+                let supportsTypedLetOrUseBang =
+                    ceenv.cenv.g.langVersion.SupportsFeature LanguageFeature.UseBangBindingValueDiscard
+
                 //   use! x = ...
                 //   use! (x) = ...
                 //   use! (__) = ...
@@ -1802,7 +1805,7 @@ let rec TryTranslateComputationExpression
                     match pat with
                     | SynPat.Named(ident = SynIdent(id, _); isThisVal = false) -> id, pat
                     | SynPat.LongIdent(longDotId = SynLongIdent(id = [ id ])) -> id, pat
-                    | SynPat.Typed(pat = pat) -> extractIdentifierFromPattern pat
+                    | SynPat.Typed(pat = pat) when supportsTypedLetOrUseBang -> extractIdentifierFromPattern pat
                     | SynPat.Wild(m) when supportsUseBangBindingValueDiscard ->
                         // To properly call the Using(disposable) CE member, we need to convert the wildcard to a SynPat.Named
                         let tmpIdent = mkSynId m "_"

src/Compiler/FSComp.txt

@@ -1800,6 +1800,7 @@ featureSupportValueOptionsAsOptionalParameters,"Support ValueOption as valid typ
 featureSupportWarnWhenUnitPassedToObjArg,"Warn when unit is passed to a member accepting `obj` argument, e.g. `Method(o:obj)` will warn if called via `Method()`."
 featureUseBangBindingValueDiscard,"Allows use! _ = ... in computation expressions"
 featureScopedNowarn,"Support for scoped enabling / disabling of warnings by #warn and #nowarn directives, also inside modules"
+featureAllowTypedLetOrUseBang,"Allow typed let! and use! bindings in computation expressions"
 3874,lexWarnDirectiveMustBeFirst,"#nowarn/#warnon directives must appear as the first non-whitespace characters on a line"
 3875,lexWarnDirectiveMustHaveArgs,"Warn directives must have warning number(s) as argument(s)"
 3876,lexWarnDirectivesMustMatch,"There is another %s for this warning already in line %d."

src/Compiler/Facilities/LanguageFeatures.fs

@@ -101,6 +101,7 @@ type LanguageFeature =
     | WarnWhenUnitPassedToObjArg
     | UseBangBindingValueDiscard
     | ScopedNowarn
+    | AllowTypedLetOrUseBang
 
 /// LanguageVersion management
 type LanguageVersion(versionText) =
@@ -233,6 +234,7 @@ type LanguageVersion(versionText) =
                 LanguageFeature.WarnWhenUnitPassedToObjArg, previewVersion
                 LanguageFeature.UseBangBindingValueDiscard, previewVersion
                 LanguageFeature.ScopedNowarn, previewVersion
+                LanguageFeature.AllowTypedLetOrUseBang, previewVersion
             ]
 
     static let defaultLanguageVersion = LanguageVersion("default")
@@ -397,6 +399,7 @@ type LanguageVersion(versionText) =
         | LanguageFeature.WarnWhenUnitPassedToObjArg -> FSComp.SR.featureSupportWarnWhenUnitPassedToObjArg ()
         | LanguageFeature.UseBangBindingValueDiscard -> FSComp.SR.featureUseBangBindingValueDiscard ()
         | LanguageFeature.ScopedNowarn -> FSComp.SR.featureScopedNowarn ()
+        | LanguageFeature.AllowTypedLetOrUseBang -> FSComp.SR.featureAllowTypedLetOrUseBang ()
 
     /// Get a version string associated with the given feature.
     static member GetFeatureVersionString feature =

src/Compiler/Facilities/LanguageFeatures.fsi

@@ -92,6 +92,7 @@ type LanguageFeature =
     | WarnWhenUnitPassedToObjArg
     | UseBangBindingValueDiscard
     | ScopedNowarn
+    | AllowTypedLetOrUseBang
 
 /// LanguageVersion management
 type LanguageVersion =