std/strutils split return type differs when being set as a variable compared to used as an argument

Description

When trying to collect a table from parsing some string input with split from std/strutils, I encountered a compiler error I don't fully understand. Is this a bug or something I need help understanding about Nim?

I distilled my original code down to the following, which reproduces the issue:

import std/strutils
import std/sugar
import std/tables

type
    MyObject = object
        a: int
        b: seq[string]

let table = collect:
    for x in 0..1:
        {x: MyObject(a: 1, b: "".split(", "))}

Nim Version

active boot switches: -d:release

Current Output

nim c repo.nim
Hint: used config file '/Users/eric/.choosenim/toolchains/nim-1.6.14/config/nim.cfg' [Conf]
Hint: used config file '/Users/eric/.choosenim/toolchains/nim-1.6.14/config/config.nims' [Conf]
................................................................................
/Users/eric/repos/nim.git/repo.nim(10, 13) template/generic instantiation of `collect` from here
/Users/eric/repos/nim.git/repo.nim(12, 29) Error: type mismatch: got 'string' for 'split("", ", ", -1)' but expected 'seq[string]'

Expected Output

A successful compilation.

Possible Solution

No response

Additional Information

Further investigating, I found something else odd when moving call the split outside of the object creation:

import std/strutils
import std/sugar
import std/tables

type
    MyObject = object
        a: int
        b: seq[string]

let table = collect:
    for x in 0..1:
        let s = "".split(", ")
        {x: MyObject(a: 1, b: s)}

The compiler hints the variable s is unused and the program links.

[I] eric@phosphorus ~/r/nim.git (devel)> nvim repo.nim
[I] eric@phosphorus ~/r/nim.git (devel)> nim c repo.nim
Hint: used config file '/Users/eric/.choosenim/toolchains/nim-1.6.14/config/nim.cfg' [Conf]
Hint: used config file '/Users/eric/.choosenim/toolchains/nim-1.6.14/config/config.nims' [Conf]
................................................................................
/Users/eric/repos/nim.git/repo.nim(12, 13) Hint: 's' is declared but not used [XDeclaredButNotUsed]
/Users/eric/repos/nim.git/repo.nim(10, 5) Hint: 'table' is declared but not used [XDeclaredButNotUsed]
Hint:  [Link]
Hint: gc: refc; opt: none (DEBUG BUILD, `-d:release` generates faster code)
43570 lines; 1.157s; 60.762MiB peakmem; proj: /Users/eric/repos/nim.git/repo.nim; out: /Users/eric/repos/nim.git/repo [SuccessX]

To understand my original issue further, I created the following to understand what type Nim thinks the return value of split is:

import std/strutils

let x: seq[string] = "".split(", ")
echo x
echo type(x)

let y = "".split(", ")
echo y
echo type(y)

echo "".split(", ")
echo type("".split(", "))

To my surprise, in the last set of echos, it prints as a sequence of strings, but the type is string:

./repo 
@[""]
seq[string]
@[""]
seq[string]
@[""]
string

I am beyond my depth, and I don't know if this is a bug or a known behavior I don't understand. Thanks for looking into this in advance :).

nim-lang / Nim