Fix missing message with type error (FS0001) (#17516)

Author: edgarfgp

docs/release-notes/.FSharp.Compiler.Service/9.0.100.md

@@ -6,6 +6,7 @@
 * C# protected property can be assigned in F# inherit constructor call. ([Issue #13299](https://github.com/dotnet/fsharp/issues/13299), [PR #17391](https://github.com/dotnet/fsharp/pull/17391))
 * MethodAccessException on equality comparison of a record with private fields. ([Issue #17447](https://github.com/dotnet/fsharp/issues/17447), [PR #17391](https://github.com/dotnet/fsharp/pull/17467))
 * Compiler fails to recognise namespace in FQN with enabled GraphBasedChecking. ([Issue #17508](https://github.com/dotnet/fsharp/issues/17508), [PR #17510](https://github.com/dotnet/fsharp/pull/17510))
+* Fix missing message for type error (FS0001). ([Issue #17373](https://github.com/dotnet/fsharp/issues/17373), [PR #17516](https://github.com/dotnet/fsharp/pull/17516))
 
 ### Added
 

src/Compiler/Driver/CompilerDiagnostics.fs

@@ -809,7 +809,7 @@ type Exception with
 
         | ErrorFromAddingTypeEquation(error = ConstraintSolverError _ as e) -> e.Output(os, suggestNames)
 
-        | ErrorFromAddingTypeEquation(_g, denv, ty1, ty2, ConstraintSolverTupleDiffLengths(_, contextInfo, tl1, tl2, _, _), m) ->
+        | ErrorFromAddingTypeEquation(_g, denv, ty1, ty2, ConstraintSolverTupleDiffLengths(_, contextInfo, tl1, tl2, m1, m2), m) ->
             let ty1, ty2, tpcs = NicePrint.minimalStringsOfTwoTypes denv ty1 ty2
             let messageArgs = tl1.Length, ty1, tl2.Length, ty2
 
@@ -826,6 +826,11 @@ type Exception with
                     else
                         os.AppendString(FSComp.SR.listElementHasWrongTypeTuple messageArgs)
                 | _ -> os.AppendString(ErrorFromAddingTypeEquationTuplesE().Format tl1.Length ty1 tl2.Length ty2 tpcs)
+            else
+                os.AppendString(ConstraintSolverTupleDiffLengthsE().Format tl1.Length tl2.Length)
+
+                if m1.StartLine <> m2.StartLine then
+                    os.AppendString(SeeAlsoE().Format(stringOfRange m1))
 
         | ErrorFromAddingTypeEquation(g, denv, ty1, ty2, e, _) ->
             if not (typeEquiv g ty1 ty2) then

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

@@ -351,3 +351,22 @@ let f4 =
             (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'    ")
         ]
 
+    [<Fact>]
+    let ``Error when tuples have differing lengths and we do not know the types.``() =
+        Fsx """
+let foo items =
+    for (a,b,c) in items do
+        printfn "%A" (a, c)
+
+[<EntryPoint>]
+let main args =
+    foo ({1..10} |> Seq.pairwise)
+    0
+        """
+        |> asExe
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 1, Line 8, Col 21, Line 8, Col 33, "The tuples have differing lengths of 3 and 2")
+        ]
+