Issue description

When using the |> operator on a partially applied function, the compiler will show a red squiggle on the RHS rather than the LHS.

Choose one or more from the following categories of impact

• Unexpected nullness warning (false positive in nullness checking, code uses --checknulls and langversion:preview).
• Missing nullness warning in a case which can produce nulls (false negative, code uses --checknulls and langversion:preview).
• Breaking change related to older null constructs in code not using the checknulls switch.
• Breaking change related to generic code and explicit type constraints (null, not null).
• Type inference issue (i.e. code worked without type annotations before, and applying the --checknulls enforces type annotations).
• C#/F# interop issue related to nullness metadata.
• Other (none of the categories above apply).

Operating System

Windows (Default)

What .NET runtime/SDK kind are you seeing the issue on

.NET SDK (.NET Core, .NET 5+)

.NET Runtime/SDK version

No response

Reproducible code snippet and actual behavior

Wrong (current behaviour):

let foo a b = "hello" + a + b
let bar : string | null = "test"
let result = bar |> foo "mr" // red squiggly shows incorrectly on 'foo mr'

Possible workarounds

Don't use |>

let foo a b = "hello" + a + b
let bar : string | null = "test"
let result = foo "mr" bar // red squiggly shows correctly on 'bar`