---
tags: improving-overlay-err-msgs
---
# First round `ytt` overlay error message guide
The purpose of this doc is to enumerate the overlay error messages possibilities and the new desired output for each scenario.
## Overlay errors
### Type mismatch
#### Expected Map but was array
##### Current
```
Overlaying (in following order: overlay.yml):
Document on line overlay.yml:3:
Map item (key 'clients') on line overlay.yml:4:
Expected map, but was *yamlmeta.Array
```
##### New
```
ytt: Error: Overlaying (in order: overlay.yml):
Type mismatch:
overlay.yml:4 (map item, 'clients') expects a map
config.yml:2 (map item, 'clients') has an array.
overlay.yml:4
3: ---
4: clients:
5: client1:
config.yml:2
1: ---
2: clients:
3: - client1:
```
### Expects mismatch
#### Not Enough Documents
##### Current
```
Overlaying (in following order: overlay.yml):
Document on line overlay.yml:3:
Expected number of matched nodes to be 2, but was 1 (lines: config.yml:1)
```
##### New
```
ytt: Error: Overlaying (in order: overlay.yml):
Expected:
overlay.yml:3 (document, '---') to match 2 item in
config.yml:1 (document, '---') but matched 1.
overlay.yml:3
2: #@overlay/match by=overlay.all, expects=2
3: ---
config.yml:1
1: ---
```
#### Too Many Documents
##### Current
```
Overlaying (in following order: overlay.yml):
Document on line overlay.yml:3:
Expected number of matched nodes to be 0, but was 1 (lines: config.yml:1)
```
##### New
```
ytt: Error: Overlaying (in order: overlay.yml):
Expected:
overlay.yml:3 (document, '---') to match 0 item in
config.yml:1 (document, '---') but matched 1.
overlay.yml:3
2: #@overlay/match by=overlay.all, expects=0
3: ---
config.yml:1
1: ---
```
#### Not Enough Map Items
##### Current
```
Overlaying (in following order: overlay.yml):
Document on line overlay.yml:3:
Map item (key 'clients') on line overlay.yml:5:
Expected number of matched nodes to be 2, but was 1 (lines: config.yml:2)
```
##### New
```
ytt: Error: Overlaying (in order: overlay.yml):
Expected:
overlay.yml:5 (map item, 'clients') to match 2 item in
config.yml:2 (map in 'document') but matched 1.
overlay.yml:5
3: ---
4: #@overlay/match by=overlay.all, expects=2
5: clients: ~
config.yml:2
1: ---
2: clients:
```
#### Too Many Map Items
##### Current
```
Overlaying (in following order: overlay.yml):
Document on line overlay.yml:3:
Map item (key 'clients') on line overlay.yml:5:
Expected number of matched nodes to be 0, but was 1 (lines: config.yml:2)
```
##### New
```
ytt: Error: Overlaying (in order: overlay.yml):
Expected:
overlay.yml:5 (map item, 'clients') to match 0 item in
config.yml:2 (map in 'document') but matched 1.
overlay.yml:5
3: ---
4: #@overlay/match by=overlay.all, expects=0
5: clients: ~
config.yml:2
1: ---
2: clients:
```
#### Not Enough Array Items
##### Current
```
Overlaying (in following order: overlay.yml):
Document on line overlay.yml:3:
Map item (key 'clients') on line overlay.yml:4:
Array item on line overlay.yml:6:
Expected number of matched nodes to be 3, but was 2 (lines: config.yml:3, config.yml:5)
```
##### New
```
ytt: Error: Overlaying (in order: overlay.yml):
Expected:
overlay.yml:6 (array item, 'clients[0]') to match 3 item in
config.yml:3,5 (array item in 'clients[]') but matched 2.
overlay.yml:6
3: ---
4: clients:
5: #@overlay/match by=overlay.all,expects=3
6: -
config.yml:3,5
1: ---
2: clients:
3: - client1:
...
5: - client2:
```
#### Too Many Array Items
##### Current
```
Overlaying (in following order: overlay.yml):
Document on line overlay.yml:3:
Map item (key 'clients') on line overlay.yml:4:
Array item on line overlay.yml:6:
Expected number of matched nodes to be 1, but was 2 (lines: config.yml:3, config.yml:5)
```
##### New
```
ytt: Error: Overlaying (in order: overlay.yml):
Expected:
overlay.yml:6 (array item, 'clients[0]') to match 1 item in
config.yml:3,5 (array item in 'clients[]') but matched 2.
overlay.yml:6
3: ---
4: clients:
5: #@overlay/match by=overlay.all,expects=1
6: - client1: ~
config.yml:3,5
1: ---
2: clients:
3: - client1:
...
5: - client2:
```
<!---
#### Error message name template
##### Current
```
```
##### New
```
```
--->
## Use Cases
### Input
Input for all use-cases is the same:
`config.yml`
```yaml=
---
clients:
- client1:
secret: blah1
- client2:
secret: blah2
```
### Expected Map was Array
`overlay.yml`
```yaml=
#@ load("@ytt:overlay", "overlay")
#@overlay/match by=overlay.all
---
clients:
client1:
```
### Not Enough Documents
`overlay.yml`
```ymal=
#@ load("@ytt:overlay", "overlay")
#@overlay/match by=overlay.all, expects=2
---
```
### Too Many Documents
`overlay.yml`
```yaml=
#@ load("@ytt:overlay", "overlay")
#@overlay/match by=overlay.all, expects=0
---
```
### Not Enough Map Items
`overlay.yml`
```yaml=
#@ load("@ytt:overlay", "overlay")
#@overlay/match by=overlay.all
---
#@overlay/match by=overlay.all, expects=2
clients: ~
```
### Too Many Map Items
`overlay.yml`
```yaml=
#@ load("@ytt:overlay", "overlay")
#@overlay/match by=overlay.all
---
#@overlay/match by=overlay.all, expects=0
clients: ~
```
### Not Enough Array Items
`overlay.yml`
```yaml=
#@ load("@ytt:overlay", "overlay")
#@overlay/match by=overlay.all
---
clients:
#@overlay/match by=overlay.all,expects=3
-
```
### Too Many Array Items
`overlay.yml`
```yaml=
#@ load("@ytt:overlay", "overlay")
#@overlay/match by=overlay.all
---
clients:
#@overlay/match by=overlay.all,expects=1
- client1: ~
```
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