declare-and-assign.sh

#!/bin/bash -ex
f() {
  local x=$(echo oh no; false)
  echo "f: $x"
}
g() {
  local y
  y=$(echo oh no; false)
  echo "g: $y"
}
f
g

output.txt

+ f
++ echo oh no
++ false
+ local 'x=oh no'
+ echo 'f: oh no'
f: oh no
+ g
+ local y
++ echo oh no
++ false
+ y='oh no'

shellcheck.txt

In declare-and-assign.sh line 3:
  local x=$(echo oh no; false)
        ^-- SC2155: Declare and assign separately to avoid masking return values.