Terraform is unable to apply the ... operator - terraform

Question

(I use terraform 0.12.20)
I have the following snippet in my code:
locals {
x = merge(values({
for location in local.locations: location => {
for apsvc_name in var.apsvc_names: "${location}-${apsvc_name}" => {
location = location
apsvc_name = apsvc_name
}
}
})...)
The x local is then output. Applying the configuration results in:
Error: Invalid expanding argument value
on ..\..\hosting-modules\web\app_hosting.tf line 35, in locals:
35: x = merge(values({
36: for location in local.locations: location => {
37: for apsvc_name in var.apsvc_names: "${location}-${apsvc_name}" => {
38: location = location
39: apsvc_name = apsvc_name
40: }
41: }
42: })...)
The expanding argument (indicated by ...) must be of a tuple, list, or set
type.
Now if I strip the call to merge(...) and assign the result of values to x, the result is output just fine:
x = [
{
"centralus-backoffice" = {
"apsvc_name" = "backoffice"
"location" = "centralus"
}
"centralus-gateway" = {
"apsvc_name" = "gateway"
"location" = "centralus"
}
"centralus-javascriptclient" = {
"apsvc_name" = "javascriptclient"
"location" = "centralus"
}
},
{
"eastus2-backoffice" = {
"apsvc_name" = "backoffice"
"location" = "eastus2"
}
"eastus2-gateway" = {
"apsvc_name" = "gateway"
"location" = "eastus2"
}
"eastus2-javascriptclient" = {
"apsvc_name" = "javascriptclient"
"location" = "eastus2"
}
},
]
And it is clearly a list, so it should qualify for ... just fine.
What am I missing?
EDIT 1
Replacing locations with a compile time list works:
locals {
locations = ["abc", "xyz"]
x = merge(values({
for location in local.locations: location => {
for apsvc_name in var.apsvc_names: "${location}-${apsvc_name}" => {
location = location
apsvc_name = apsvc_name
}
}
})...)
}
Which results in:
Outputs:
x = {
"abc-backoffice" = {
"apsvc_name" = "backoffice"
"location" = "abc"
}
"abc-gateway" = {
"apsvc_name" = "gateway"
"location" = "abc"
}
"abc-javascriptclient" = {
"apsvc_name" = "javascriptclient"
"location" = "abc"
}
"xyz-backoffice" = {
"apsvc_name" = "backoffice"
"location" = "xyz"
}
"xyz-gateway" = {
"apsvc_name" = "gateway"
"location" = "xyz"
}
"xyz-javascriptclient" = {
"apsvc_name" = "javascriptclient"
"location" = "xyz"
}
}
But replace "abc" with a variable value and it stops working:
locals {
locations = [var.primary_location, "xyz"]
x = merge(values({
for location in local.locations: location => {
for apsvc_name in var.apsvc_names: "${location}-${apsvc_name}" => {
location = location
apsvc_name = apsvc_name
}
}
})...)
}
And bang:
Error: Invalid expanding argument value
on ..\..\hosting-modules\web\app_hosting.tf line 5, in locals:
5: x = merge(values({
6: for location in local.locations: location => {
7: for apsvc_name in var.apsvc_names: "${location}-${apsvc_name}" => {
8: location = location
9: apsvc_name = apsvc_name
10: }
11: }
12: })...)
|----------------
| local.locations is tuple with 2 elements
The expanding argument (indicated by ...) must be of a tuple, list, or set
type.
EDIT 2
So, the code that should work (I improved it - values is not needed):
merge([
for location in local.locations: {
for apsvc_name in var.apsvc_names: "${location}-${apsvc_name}" => {
location = location
apsvc_name = apsvc_name
}
}
]...)
does not work for mysterious reasons. I ended up with the following workaround:
_y1 = [
for location in local.locations: {
for apsvc_name in var.apsvc_names: "${location}-${apsvc_name}" => {
location = location
apsvc_name = apsvc_name
}
}
]
_y2 = flatten([for m in local._y1: [for k,v in m: {
key = k
value = v
}]])
x = zipmap(local._y2.*.key, local._y2.*.value)
That one does work.
EDIT 3
https://github.com/hashicorp/terraform/issues/24033