Allow closing '>' of multiline nested type arguments to align with the opener (#15171)

docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

@@ -3,6 +3,7 @@
 * Semantic classification no longer marks recursive object self-references (`as this`, `let rec` self-refs) as mutable. ([Issue #5229](https://github.com/dotnet/fsharp/issues/5229))
 * Fix `MethodAccessException` under `--realsig+` when a closure (inner `let rec`, `task`/`async` state machine, or quotation splice) inside a member defined in an intrinsic type augmentation (`type C with member ...`) accesses a `private` member of `C`. The synthesized closure is now nested inside the declaring type instead of beside it in the module class. ([Issue #19933](https://github.com/dotnet/fsharp/issues/19933), [PR #19955](https://github.com/dotnet/fsharp/pull/19955))
 * Preserve source range for type errors on empty-bodied computation expressions (e.g. `foo {}`) in pipelines, function arguments, and type-annotated contexts, instead of reporting `unknown(1,1)`. ([Issue #19550](https://github.com/dotnet/fsharp/issues/19550), [PR #19849](https://github.com/dotnet/fsharp/pull/19849))
+* Fix multiline nested type arguments failing to parse when the closing `>` aligns with the opening type name's column. ([Issue #15171](https://github.com/dotnet/fsharp/issues/15171))
 * Tooltip "Full name" now shows demangled companion module names (e.g. `MyType.func` instead of `MyTypeModule.func`). ([Issue #17335](https://github.com/dotnet/fsharp/issues/17335), [PR #19867](https://github.com/dotnet/fsharp/pull/19867))
 * Fix internal error (FS0193) when calling an indexed property setter with a named argument that matches an indexer parameter. ([Issue #16034](https://github.com/dotnet/fsharp/issues/16034), [PR #19851](https://github.com/dotnet/fsharp/pull/19851))
 * Fix missing FS1182 ("unused binding") warning for unused `let` function bindings inside class types. ([Issue #13849](https://github.com/dotnet/fsharp/issues/13849), [PR #19805](https://github.com/dotnet/fsharp/pull/19805))

src/Compiler/SyntaxTree/LexFilter.fs

@@ -383,6 +383,11 @@ let rec isSeqBlockElementContinuator token =
     //              Shortcut.CtrlO)
     | END | AND | WITH | THEN | RPAREN | RBRACE _ | BAR_RBRACE | RBRACK | BAR_RBRACK | RQUOTE _ -> true
 
+    // A closing '>' of a (possibly multiline) type-argument list is a closing bracket, like ')' or ']'
+    // above: it may align with the first column of a sequence block without starting a new element.
+    // See dotnet/fsharp#15171.
+    | GREATER true -> true
+
     // The following arise during reprocessing of the inserted tokens when we hit a DONE
     | ORIGHT_BLOCK_END _ | OBLOCKEND _ | ODECLEND (_, _) -> true
     | ODUMMY token -> isSeqBlockElementContinuator token

tests/FSharp.Compiler.ComponentTests/Conformance/LexicalFiltering/OffsideExceptions/MultilineNestedTypeArguments.fs

@@ -0,0 +1,17 @@
+// #Regression #Conformance #LexFilter #Exceptions
+// https://github.com/dotnet/fsharp/issues/15171
+// The closing '>' of a nested, multiline type-argument list may align with the column of the
+// opening type name (here the inner 'Foo'); it must not be treated as a new sequence-block item.
+
+open System
+
+type Bar = class end
+type Foo<'a> = class end
+
+type Terminal =
+    abstract onKey:
+        IEvent<
+            Foo<
+                Bar * int
+            >
+        > with get, set

tests/FSharp.Compiler.ComponentTests/Conformance/LexicalFiltering/OffsideExceptions/OffsideExceptions.fs

@@ -9,12 +9,23 @@ open FSharp.Test.Compiler.Assertions.StructuredResultsAsserts
 
 module OffsideExceptions =
 
+    // https://github.com/dotnet/fsharp/issues/15171
+    // The closing '>' of a nested multiline type-argument list may align with the opening type name.
+    [<Theory; FileInlineData("MultilineNestedTypeArguments.fs")>]
+    let MultilineNestedTypeArguments compilation =
+        compilation
+        |> getCompilation
+        |> asFsx
+        |> typecheck
+        |> shouldSucceed
+        |> ignore
+
     // This test was automatically generated (moved from FSharpQA suite - Conformance/LexicalFiltering/Basic/OffsideExceptions)
     //<Expects status="success"></Expects>
     [<Theory; FileInlineData("InfixTokenPlusOne.fs")>]
     let InfixTokenPlusOne compilation =
         compilation
-        |> getCompilation 
+        |> getCompilation
         |> asFsx
         |> typecheck
         |> shouldSucceed

tests/service/data/SyntaxTree/SynType/SynTypeAppNestedMultilineClosingGreaterAligned.fs

@@ -0,0 +1,7 @@
+type T =
+    abstract M:
+        A<
+            B<
+                int
+            >
+        >

tests/service/data/SyntaxTree/SynType/SynTypeAppNestedMultilineClosingGreaterAligned.fs.bsl

@@ -0,0 +1,49 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/SynType/SynTypeAppNestedMultilineClosingGreaterAligned.fs", false,
+      QualifiedNameOfFile SynTypeAppNestedMultilineClosingGreaterAligned, [],
+      [SynModuleOrNamespace
+         ([SynTypeAppNestedMultilineClosingGreaterAligned], false, AnonModule,
+          [Types
+             ([SynTypeDefn
+                 (SynComponentInfo
+                    ([], None, [], [T],
+                     PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector),
+                     false, None, (1,5--1,6)),
+                  ObjectModel
+                    (Unspecified,
+                     [AbstractSlot
+                        (SynValSig
+                           ([], SynIdent (M, None),
+                            SynValTyparDecls (None, true),
+                            App
+                              (LongIdent (SynLongIdent ([A], [], [None])),
+                               Some (3,9--3,10),
+                               [App
+                                  (LongIdent (SynLongIdent ([B], [], [None])),
+                                   Some (4,13--4,14),
+                                   [LongIdent (SynLongIdent ([int], [], [None]))],
+                                   [], Some (6,12--6,13), false, (4,12--6,13))],
+                               [], Some (7,8--7,9), false, (3,8--7,9)),
+                            SynValInfo ([], SynArgInfo ([], false, None)), false,
+                            false,
+                            PreXmlDoc ((2,4), FSharp.Compiler.Xml.XmlDocCollector),
+                            Single None, None, (2,4--7,9),
+                            { LeadingKeyword = Abstract (2,4--2,12)
+                              InlineKeyword = None
+                              WithKeyword = None
+                              EqualsRange = None }),
+                         { IsInstance = true
+                           IsDispatchSlot = true
+                           IsOverrideOrExplicitImpl = false
+                           IsFinal = false
+                           GetterOrSetterIsCompilerGenerated = false
+                           MemberKind = PropertyGet }, (2,4--7,9),
+                         { GetSetKeywords = None })], (2,4--7,9)), [], None,
+                  (1,5--7,9), { LeadingKeyword = Type (1,0--1,4)
+                                EqualsRange = Some (1,7--1,8)
+                                WithKeyword = None })], (1,0--7,9))],
+          PreXmlDocEmpty, [], None, (1,0--8,0), { LeadingKeyword = None })],
+      (true, true), { ConditionalDirectives = []
+                      WarnDirectives = []
+                      CodeComments = [] }, set []))