Indentation of the then statement in case expressions

[f-tremblay]

Describe the bug
In case expressions, when there are long when statements, sqlfmt put the then statements at the same indentation as the when statements, which makes them harder to read.
If we look at the dbt style guide (e.g. here and here), the then is more indented.

To Reproduce

with
  source as (select * from {{ source("my_application", "users") }}),
  renamed as (
      select
          sum(
              case when order_status = 'complete' then order_total end
          ) as monthly_total,
          nullif(
              trim(
                  case
                      when regexp_count(nullif(full_name, ''), ' ') = 0
                      then nullif(full_name, '')
                      when regexp_count(nullif(full_name, ''), ' ') = 1
                      then split_part(nullif(full_name, ''), ' ', 1)
                      -- this user has more than two names!
                      else regexp_substr(nullif(full_name, ''), '.* .* ')
                  end
              )

              from source
          )
      select *
      from renamed

Expected behavior

with
  source as (select * from {{ source("my_application", "users") }}),
  renamed as (
      select
          sum(
              case when order_status = 'complete' then order_total end
          ) as monthly_total,
          nullif(
              trim(
                  case
                      when regexp_count(nullif(full_name, ''), ' ') = 0
                          then nullif(full_name, '')
                      when regexp_count(nullif(full_name, ''), ' ') = 1
                          then split_part(nullif(full_name, ''), ' ', 1)
                      -- this user has more than two names!
                      else regexp_substr(nullif(full_name, ''), '.* .* ')
                  end
              )

              from source
          )
      select *
      from renamed

Actual behavior
thenare not indented properly (see To Reproduce )

Additional context
What is the output of sqlfmt --version?
sqlfmt, version 0.13.0

[tconbeer]

@f-tremblay Thanks for the feedback. This is the intended behavior, so I've moved this to a discussion.

I think indented then (like join) has its merits, but I intentionally diverged from the dbt style guide for the following reasons:

1. Keeping when, then, and else at the same depth makes the code much simpler

2. There will always be collisions with then. If you indent then, it can blend in with complex conditionals:

   case
       when
           fooooooo.barrrrrrr = another_table.another_column
           and fooooooo.barrrrrrr = another_table.another_column2
           then  fooooooo.barrrrrrr + another_table.another_column
   ...

3. What about else? The code after else is analagous to what follows then, not when. So shouldn't else have the same indentation as then? That doesn't make sense if you indent then, since else will be nested under the final when. This is especially incongruous when the statements might wrap onto a single line (I wouldn't want when and then on a single line and else on a following line).

[f-tremblay]

Thanks @tconbeer for the explanations.

For the first point, were you talking about sqlfmt's code, or the user's SQL code?

[f-tremblay]

For the second point, I will use python as an example to share my thoughts.

if foooooo == 1 and baaaaar == 1:
    out = "foooooobaaaaar"
elif foooooo == 1:
    out = "foooooo"

and

case
    when foooooo = 1 and baaaaar = 1
        then "foooooobaaaaar"
    when foooooo = 1
        then "foooooo"
end as out,

are both easy to read.

However,

if foooooo == 1 and baaaaar == 1:
out = "foooooobaaaaar"
elif foooooo == 1:
out = "foooooo"

is incorrect, and

case
    when foooooo = 1 and baaaaar = 1
    then "foooooobaaaaar"
    when foooooo = 1
    then "foooooo"
end as out,

is painful to read.
(Since the words when and then are very similar, without proper indentation, it requires extra attention not to confuse them)

These principles still apply for more complex (i.e. longer) conditions:

if (
    foooooo == 1
    and baaaaar == 1
    and another_longer_condition == "a very very long string"
):
    out = "foooooobaaaaar"
elif foooooo == 1:
    out = "foooooo"

and

case
    when
        foooooo = 1
        and baaaaar = 1
        and another_longer_condition == "a very very long string"
        then "foooooobaaaaar"
    when foooooo = 1
        then "foooooo"
end as out,

are both easy to read.

However,

if (
    foooooo == 1
    and baaaaar == 1
    and another_longer_condition == "a very very long string"
):
out = "foooooobaaaaar"
elif foooooo == 1:
out = "foooooo"

is incorrect, and

case
    when
        foooooo = 1
        and baaaaar = 1
        and another_longer_condition == "a very very long string"
    then "foooooobaaaaar"
    when foooooo = 1
    then "foooooo"
end as out,

is very confusing

[f-tremblay]

For the last point, I will also use python:

if foooooo == 1 and baaaaar == 1:
    out = "foooooobaaaaar"
elif foooooo == 1:
    out = "foooooo"
else: out = ""

is easy to read, although

if foooooo == 1 and baaaaar == 1:
    out = "foooooobaaaaar"
elif foooooo == 1:
    out = "foooooo"
else: 
    out = ""

is preferable according to many (including black).
Similarly,

case
    when foooooo = 1 and baaaaar = 1
        then "foooooobaaaaar"
    when foooooo = 1
        then "foooooo"
    else ""
end as out,

is easy to read, although

case
    when foooooo = 1 and baaaaar = 1
        then "foooooobaaaaar"
    when foooooo = 1
        then "foooooo"
    else 
        ""
end as out,

would be equally readable.

However,

if foooooo == 1 and baaaaar == 1:
out = "foooooobaaaaar"
elif foooooo == 1:
out = "foooooo"
else:
out = ""

is incorrect, and

case
    when foooooo = 1 and baaaaar = 1
    then "foooooobaaaaar"
    when foooooo = 1
    then "foooooo"
    else ""
end as out,

is confusing.

It simply does not make sense to have then at the same indentation as when and else. when and else both indicate that there's a new "case" (the number of "cases" is the number of when +else keyword(s) in a case expression), while the then keyword is to separate the condition(s) from the result expression.