Incorrect UnusedImport warning in presence of import foo as bar

[tersec]

When module bar imports and exports module foo (here, sequtils) using import ... as ... and module baz imports bar to get access to foo, either one or two UnusedImport warning is emitted, depending on Nim version.

Example

test.nim:

import sequtils as su2
export su2

test2.nim:

import "."/test
echo repeat("b", 3)

Current Output

$ ~/Nim/bin/nim c -r test2.nim
Hint: used config file 'Nim/config/nim.cfg' [Conf]
Hint: used config file 'Nim/config/config.nims' [Conf]
.......
test.nim(1, 17) Warning: imported and not used: 'sequtils' [UnusedImport]
test2.nim(1, 11) Warning: imported and not used: 'test' [UnusedImport]
CC: stdlib_assertions.nim
CC: stdlib_io.nim
CC: stdlib_system.nim
CC: test2.nim
Hint:  [Link]
Hint: 25592 lines; 0.530s; 31.934MiB peakmem; Debug build; proj: test2.nim; out: test2 [SuccessX]
Hint: test2  [Exec]
@["b", "b", "b"]
user@tertiva:~$ ~/Nim/bin/nim --version
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2021-03-25
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 8573160a44439ffe3fbbdd354188db9c976a2081
active boot switches: -d:release

Older versions also display variations of this behavior.
1.4.2:

$ nim c -r test2.nim
Hint: used config file '/etc/nim/nim.cfg' [Conf]
Hint: used config file '/etc/nim/config.nims' [Conf]
.......
test.nim(1, 17) Warning: imported and not used: 'sequtils' [UnusedImport]
CC: stdlib_assertions.nim
CC: stdlib_dollars.nim
CC: stdlib_io.nim
CC: stdlib_system.nim
CC: stdlib_sequtils.nim
CC: test2.nim
Hint:  [Link]
Hint: 25242 lines; 0.542s; 25.52MiB peakmem; Debug build; proj: test2.nim; out: test2 [SuccessX]
Hint: test2  [Exec]
@["b", "b", "b"]
$ nim --version
Nim Compiler Version 1.4.2 [Linux: amd64]
Compiled at 2020-12-02
Copyright (c) 2006-2020 by Andreas Rumpf

active boot switches: -d:release

1.2.6:

$ Nim1.2.6/bin/nim c -r test2.nim
Hint: used config file 'Nim1.2.6/config/nim.cfg' [Conf]
Hint: used config file 'Nim1.2.6/config/config.nims' [Conf]
Hint: system [Processing]
Hint: widestrs [Processing]
Hint: io [Processing]
Hint: test2 [Processing]
Hint: test [Processing]
Hint: sequtils [Processing]
Hint: macros [Processing]
/home/user/test.nim(1, 17) Warning: imported and not used: 'sequtils' [UnusedImport]
CC: stdlib_assertions.nim
CC: stdlib_dollars.nim
CC: stdlib_io.nim
CC: stdlib_system.nim
CC: stdlib_sequtils.nim
CC: test2.nim
Hint:  [Link]
Hint: 25264 LOC; 0.532 sec; 30.262MiB peakmem; Debug build; proj: test2.nim; out: test2 [SuccessX]
Hint: test2  [Exec]
@["b", "b", "b"]
$ Nim1.2.6/bin/nim --version
Nim Compiler Version 1.2.6 [Linux: amd64]
Compiled at 2021-03-24
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: f05ba3c667157f46f141ff700121c7aff86cf07a
active boot switches: -d:release

1.0.4:

$ nim c -r test2.nim
Hint: used config file '/etc/nim/nim.cfg' [Conf]
Hint: used config file '/etc/nim/config.nims' [Conf]
Hint: system [Processing]
Hint: widestrs [Processing]
Hint: io [Processing]
Hint: test2 [Processing]
Hint: test [Processing]
Hint: sequtils [Processing]
Hint: macros [Processing]
test.nim(1, 17) Warning: imported and not used: 'sequtils' [UnusedImport]
CC: stdlib_assertions.nim
CC: stdlib_dollars.nim
CC: stdlib_io.nim
CC: stdlib_system.nim
CC: stdlib_sequtils.nim
CC: test2.nim
Hint:  [Link]
Hint: operation successful (25045 lines compiled; 0.523 sec total; 29.773MiB peakmem; Debug Build) [SuccessX]
Hint: test2  [Exec]
@["b", "b", "b"]
$ nim --version
Nim Compiler Version 1.0.4 [Linux: amd64]
Compiled at 2020-02-04
Copyright (c) 2006-2019 by Andreas Rumpf

active boot switches: -d:release

Expected Output

No incorrect UnusedImport warning(s).

Additional Information

#17510 is related, but only appears after Nim 1.4.2 and doesn't need import foo as bar / export bar, just import foo / export foo.