Fix for offside errors on interpolated expressions

src/Compiler/SyntaxTree/LexFilter.fs

@@ -1563,9 +1563,11 @@ type LexFilterImpl (
             | INTERP_STRING_PART _ ->
                 pushCtxt tokenTup (CtxtParen (token, tokenTup.LexbufState.EndPos))
                 pushCtxtSeqBlock tokenTup NoAddBlockEnd
+            | INTERP_STRING_END _ -> ()
             | _ ->
                 // Queue a dummy token at this position to check if any closing rules apply
                 delayToken(pool.UseLocation(tokenTup, ODUMMY token))
+
             returnToken tokenLexbufState token
 
         // Balancing rule. Encountering a 'end' can balance with a 'with' but only when not offside

tests/FSharp.Compiler.ComponentTests/Language/InterpolatedStringsTests.fs

@@ -109,4 +109,23 @@ let s = $"...%-%...{0}"
         """
         |> compile
         |> shouldFail
-        |> withSingleDiagnostic (Warning 3376, Line 2, Col 9, Line 2, Col 24, "Bad format specifier: '%'")
+        |> withSingleDiagnostic (Warning 3376, Line 2, Col 9, Line 2, Col 24, "Bad format specifier: '%'")
+
+    [<Fact>]
+    let ``Interpolated expression can be offside`` () =
+        Fsx """
+let a() =
+    let b() =
+        $"
+{1}"
+    b()
+
+type Foo () =
+    member _.Bar () =
+        let x =
+            $"
+{2}"
+        x
+        """
+        |> compile
+        |> shouldSucceed

tests/service/data/SyntaxTree/String/InterpolatedStringOffsideInModule.fs

@@ -0,0 +1,4 @@
+module A =
+    let b =
+        $"
+{0}"

tests/service/data/SyntaxTree/String/InterpolatedStringOffsideInModule.fs.bsl

@@ -0,0 +1,34 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/String/InterpolatedStringOffsideInModule.fs", false,
+      QualifiedNameOfFile InterpolatedStringOffsideInModule, [], [],
+      [SynModuleOrNamespace
+         ([InterpolatedStringOffsideInModule], false, AnonModule,
+          [NestedModule
+             (SynComponentInfo
+                ([], None, [], [A],
+                 PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), false,
+                 None, (1,0--1,8)), false,
+              [Let
+                 (false,
+                  [SynBinding
+                     (None, Normal, false, false, [],
+                      PreXmlDoc ((2,4), FSharp.Compiler.Xml.XmlDocCollector),
+                      SynValData
+                        (None, SynValInfo ([], SynArgInfo ([], false, None)),
+                         None),
+                      Named (SynIdent (b, None), false, None, (2,8--2,9)), None,
+                      InterpolatedString
+                        ([String ("
+", (3,8--4,1));
+                          FillExpr (Const (Int32 0, (4,1--4,2)), None);
+                          String ("", (4,2--4,4))], Regular, (3,8--4,4)),
+                      (2,8--2,9), Yes (2,4--4,4),
+                      { LeadingKeyword = Let (2,4--2,7)
+                        InlineKeyword = None
+                        EqualsRange = Some (2,10--2,11) })], (2,4--4,4))], false,
+              (1,0--4,4), { ModuleKeyword = Some (1,0--1,6)
+                            EqualsRange = Some (1,9--1,10) })], PreXmlDocEmpty,
+          [], None, (1,0--4,4), { LeadingKeyword = None })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))

tests/service/data/SyntaxTree/String/InterpolatedStringOffsideInNestedLet.fs

@@ -0,0 +1,5 @@
+let a =
+    let b =
+        $"
+{0}"
+    b

tests/service/data/SyntaxTree/String/InterpolatedStringOffsideInNestedLet.fs.bsl

@@ -0,0 +1,40 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/String/InterpolatedStringOffsideInNestedLet.fs", false,
+      QualifiedNameOfFile InterpolatedStringOffsideInNestedLet, [], [],
+      [SynModuleOrNamespace
+         ([InterpolatedStringOffsideInNestedLet], false, AnonModule,
+          [Let
+             (false,
+              [SynBinding
+                 (None, Normal, false, false, [],
+                  PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector),
+                  SynValData
+                    (None, SynValInfo ([], SynArgInfo ([], false, None)), None),
+                  Named (SynIdent (a, None), false, None, (1,4--1,5)), None,
+                  LetOrUse
+                    (false, false,
+                     [SynBinding
+                        (None, Normal, false, false, [],
+                         PreXmlDoc ((2,4), FSharp.Compiler.Xml.XmlDocCollector),
+                         SynValData
+                           (None, SynValInfo ([], SynArgInfo ([], false, None)),
+                            None),
+                         Named (SynIdent (b, None), false, None, (2,8--2,9)),
+                         None,
+                         InterpolatedString
+                           ([String ("
+", (3,8--4,1));
+                             FillExpr (Const (Int32 0, (4,1--4,2)), None);
+                             String ("", (4,2--4,4))], Regular, (3,8--4,4)),
+                         (2,8--2,9), Yes (2,4--4,4),
+                         { LeadingKeyword = Let (2,4--2,7)
+                           InlineKeyword = None
+                           EqualsRange = Some (2,10--2,11) })], Ident b,
+                     (2,4--5,5), { InKeyword = None }), (1,4--1,5), NoneAtLet,
+                  { LeadingKeyword = Let (1,0--1,3)
+                    InlineKeyword = None
+                    EqualsRange = Some (1,6--1,7) })], (1,0--5,5))],
+          PreXmlDocEmpty, [], None, (1,0--5,5), { LeadingKeyword = None })],
+      (true, true), { ConditionalDirectives = []
+                      CodeComments = [] }, set []))