Fix inference for same (but distinct) record types in seq CE (#16040)

* Try TcExprFlex

Seems like it could be done better, right now there are two type
checking passes for same expression

* Fix tests

This should be okay, because in both cases, the error message basically
says the same thing.

* Add a unit test

src/Compiler/Checking/CheckComputationExpressions.fs

@@ -2210,14 +2210,15 @@ let TcSequenceExpression (cenv: cenv) env tpenv comp (overallTy: OverallTy) m =
 
             let env = { env with eContextInfo = ContextInfo.SequenceExpression genOuterTy }
 
-            if enableImplicitYield then 
+            if enableImplicitYield then
                 let hasTypeUnit, expr, tpenv = TryTcStmt cenv env tpenv comp
                 if hasTypeUnit then 
                     Choice2Of2 expr, tpenv
                 else
                     let genResultTy = NewInferenceType g
                     let mExpr = expr.Range
                     UnifyTypes cenv env mExpr genOuterTy (mkSeqTy cenv.g genResultTy)
+                    let expr, tpenv = TcExprFlex cenv flex true genResultTy env tpenv comp
                     let exprTy = tyOfExpr cenv.g expr
                     AddCxTypeMustSubsumeType env.eContextInfo env.DisplayEnv cenv.css mExpr NoTrace genResultTy exprTy
                     let resExpr = mkCallSeqSingleton cenv.g mExpr genResultTy (mkCoerceExpr(expr, genResultTy, mExpr, exprTy))

tests/FSharp.Compiler.ComponentTests/ErrorMessages/TypeMismatchTests.fs

@@ -345,9 +345,9 @@ let f4 =
         |> typecheck
         |> shouldFail
         |> withDiagnostics [
-            (Error 193,   Line 6,  Col 9,  Line 6,  Col 16, "Type constraint mismatch. The type \n    'string'    \nis not compatible with type\n    'int'    \n")
-            (Error 193,   Line 12, Col 13, Line 12, Col 16, "Type constraint mismatch. The type \n    'string'    \nis not compatible with type\n    'int'    \n")
+            (Error 1,   Line 6,  Col 9,  Line 6,  Col 16, "This expression was expected to have type\n    'int'    \nbut here has type\n    'string'    ")
+            (Error 1,   Line 12, Col 13, Line 12, Col 16, "This expression was expected to have type\n    'int'    \nbut here has type\n    'string'    ")
             (Error 193,   Line 21, Col 9,  Line 21, Col 24, "Type constraint mismatch. The type \n    'int list'    \nis not compatible with type\n    'string seq'    \n")
-            (Error 193,   Line 28, Col 9,  Line 28, Col 12, "Type constraint mismatch. The type \n    'float'    \nis not compatible with type\n    'int64'    \n")
+            (Error 1,   Line 28, Col 9,  Line 28, Col 12, "This expression was expected to have type\n    'int64'    \nbut here has type\n    'float'    ")
         ]
 

tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj

@@ -226,6 +226,7 @@
     <Compile Include="Interop\StaticsInInterfaces.fs" />
     <Compile Include="Interop\VisibilityTests.fs" />
     <Compile Include="Scripting\Interactive.fs" />
+    <Compile Include="TypeChecks\SeqTypeCheckTests.fs" />
     <Compile Include="TypeChecks\CheckDeclarationsTests.fs" />
     <Compile Include="TypeChecks\Graph\Utils.fs" />
     <Compile Include="TypeChecks\Graph\QueryTrieTests.fs" />

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

@@ -414,8 +414,8 @@ let typedSeq =
     |> withLangVersion80
     |> typecheck
     |> shouldFail
-    |> withErrorCode 193
-    |> withDiagnosticMessageMatches "Type constraint mismatch"
+    |> withErrorCode 1
+    |> withDiagnosticMessageMatches "This expression was expected to have type"
 
 
 [<Literal>]

tests/FSharp.Compiler.ComponentTests/TypeChecks/SeqTypeCheckTests.fs

@@ -0,0 +1,17 @@
+module TypeChecks.SeqTypeCheckTests
+
+open Xunit
+open FSharp.Test.Compiler
+
+[<Fact>]
+let ``Seq expr with impicit yield type checks correctly when two identical record types are present`` () =
+    FSharp """
+module SeqInference
+
+type A = { X: int }
+type B = { X: int }
+
+let l: A list = [ if true then { X = 42 } ]
+"""
+    |> typecheck
+    |> shouldSucceed

tests/fsharp/typecheck/sigs/neg24.bsl

@@ -21,11 +21,15 @@ neg24.fs(302,33,302,34): typecheck error FS0001: All elements of a list must be
 
 neg24.fs(302,36,302,37): typecheck error FS0001: All elements of a list must be implicitly convertible to the type of the first element, which here is 'unit'. This element has type 'int'.
 
-neg24.fs(305,24,305,25): typecheck error FS0193: Type constraint mismatch. The type 
-    'int'    
-is not compatible with type
+neg24.fs(305,24,305,25): typecheck error FS0001: This expression was expected to have type
     'unit'    
+but here has type
+    'int'    
 
+neg24.fs(305,31,305,32): typecheck error FS0001: This expression was expected to have type
+    'unit'    
+but here has type
+    'int'    
 
 neg24.fs(308,30,308,31): typecheck error FS0020: The result of this expression has type 'int' and is implicitly ignored. Consider using 'ignore' to discard this value explicitly, e.g. 'expr |> ignore', or 'let' to bind the result to a name, e.g. 'let result = expr'.
 

tests/fsharp/typecheck/sigs/version47/neg24.bsl

@@ -21,11 +21,15 @@ neg24.fs(302,33,302,34): typecheck error FS0001: All elements of a list must be
 
 neg24.fs(302,36,302,37): typecheck error FS0001: All elements of a list must be implicitly convertible to the type of the first element, which here is 'unit'. This element has type 'int'.
 
-neg24.fs(305,24,305,25): typecheck error FS0193: Type constraint mismatch. The type 
-    'int'    
-is not compatible with type
+neg24.fs(305,24,305,25): typecheck error FS0001: This expression was expected to have type
     'unit'    
+but here has type
+    'int'    
 
+neg24.fs(305,31,305,32): typecheck error FS0001: This expression was expected to have type
+    'unit'    
+but here has type
+    'int'    
 
 neg24.fs(308,30,308,31): typecheck error FS0020: The result of this expression has type 'int' and is implicitly ignored. Consider using 'ignore' to discard this value explicitly, e.g. 'expr |> ignore', or 'let' to bind the result to a name, e.g. 'let result = expr'.