im pretty sure this will not work because it doesnt have a key so resource should fail
could we maybe move this logic to aci_tenants.tf and pass the values there?

This was tested using static routes and they were pushed properly into APIC because key are defined using 0.0.0.0/0 as next hop.

Data model:

apic:
  tenants:
    - name: ABC
      l3outs:
        - name: L3OUT1
          vrf: VRF1
          domain: ROUTED1
          nodes:
            - node_id: 1001
              router_id: 5.5.5.5
              static_routes:
                - prefix: 2.2.2.0/24
                  next_hops:
                    - ip: 6.6.6.6
                - prefix: 1.1.1.1/32
                - prefix: 1.1.1.2/32

Terraform plan:

Terraform will perform the following actions:

  # module.aci.module.aci_l3out_node_profile_auto["ABC/L3OUT1"].aci_rest_managed.ipNexthopP["1001/1.1.1.1/32/0.0.0.0/0"] will be created
  + resource "aci_rest_managed" "ipNexthopP" {
      + annotation  = "orchestrator:terraform"
      + class_name  = "ipNexthopP"
      + content     = {
          + "descr"  = null
          + "nhAddr" = "0.0.0.0/0"
          + "pref"   = "unspecified"
          + "type"   = "none"
        }
      + dn          = "uni/tn-ABC/out-L3OUT1/lnodep-L3OUT1/rsnodeL3OutAtt-[topology/pod-1/node-1001]/rt-[1.1.1.1/32]/nh-[0.0.0.0/0]"
      + escape_html = true
      + id          = (known after apply)
    }

  # module.aci.module.aci_l3out_node_profile_auto["ABC/L3OUT1"].aci_rest_managed.ipNexthopP["1001/1.1.1.2/32/0.0.0.0/0"] will be created
  + resource "aci_rest_managed" "ipNexthopP" {
      + annotation  = "orchestrator:terraform"
      + class_name  = "ipNexthopP"
      + content     = {
          + "descr"  = null
          + "nhAddr" = "0.0.0.0/0"
          + "pref"   = "unspecified"
          + "type"   = "none"
        }
      + dn          = "uni/tn-ABC/out-L3OUT1/lnodep-L3OUT1/rsnodeL3OutAtt-[topology/pod-1/node-1001]/rt-[1.1.1.2/32]/nh-[0.0.0.0/0]"
      + escape_html = true
      + id          = (known after apply)
    }

Terraform apply:

Please note 0.0.0.0/0 as next hop cannot be set manually, so this creates a unique key for routes without next hop defined.

code from PR works and key value will be set up correctly:

    for node in var.nodes : [
      for sr in coalesce(node.static_routes, []) : [
        for nh in length(coalesce(sr.next_hops, [])) > 0 ? coalesce(sr.next_hops, []) : [{ ip = "0.0.0.0/0", type = "none", description = null, preference = 0, ip_sla_policy = null, track_list = null }] : {
          key = "${node.node_id}/${sr.prefix}/${nh.ip}"

we get key based on node, static route and IP. we add missing IP in "new code".
However, I am not a big fan of adding config to an resource in main.tf. Cannot we manage it on locals level just with 0.0.0.0/0 as default value in next_hops loop?

ok, i looked in the wrong line, however still i don't like having this in the module, where we can pass this data more safely from tenants.tf file

Consider that this special 0.0.0.0/0 next hop does NOT use the default values set in default file. Putting this in tenant.tf will require not only the attribute value definitions, but also conditionals to check if next_hop is 0.0.0.0/0 so that default values are not applied but hard coded.

Please confirm your preference to this approach.

make a conditional in tenants.tf to check if next hop exists, if it does pass the old code with default values, if it doesnt exist, pass these hardcoded values
to reiterate - do not do that in the main.tf

code from PR works and key value will be set up correctly:

    for node in var.nodes : [
      for sr in coalesce(node.static_routes, []) : [
        for nh in length(coalesce(sr.next_hops, [])) > 0 ? coalesce(sr.next_hops, []) : [{ ip = "0.0.0.0/0", type = "none", description = null, preference = 0, ip_sla_policy = null, track_list = null }] : {
          key = "${node.node_id}/${sr.prefix}/${nh.ip}"

we get key based on node, static route and IP. we add missing IP in "new code".
However, I am not a big fan of adding config to an resource in main.tf. Cannot we manage it on locals level just with 0.0.0.0/0 as default value in next_hops loop?

make a conditional in tenants.tf to check if next hop exists, if it does pass the old code with default values, if it doesnt exist, pass these hardcoded values
to reiterate - do not do that in the main.tf