[FEATURE] Support for indentation in 'of/else/else if' etc.

[haxscramper]

Implements nim-lang/RFCs#420

[Araq]

Needs a gramar update too. For this, patch some #| comment in parser.nim and then run nim c-r compiler/parser.nim.

[Araq]

There seems to be some nimble important_packages hiccups.

[haxscramper]

CI passed earlier with the same implementation, and it is very unlikely that grammar comment modification affected semcheck for a package (code fails with type mismatch error).

Does this mean I need to figure out what is wrong, or PR will still be accepted?

[Araq]

It means we'll close and reopen the PR this weekend until it's green.

[ringabout]

CI passed earlier with the same implementation

CI is broken which doesn't run at all but is green until this PR: #18811 (make sure you already fetch the latest commit)

[ringabout]

I don't think closing and reopening this PR helps. As I said before, the PR may break some packages (CI may be green wrongly before). So make sure the PR already bases on the latest commit. If it were, maybe you need to figure out why the cligen library is broken.

[haxscramper]

Separately executing testament for package batch 1_3, running inim tests (cligen is shown in CI, but inim test fails) with new compiler showed no issues.

[ringabout]

it is very unlikely that grammar comment modification affected semcheck for a package

IMO your PR can affect code like this

readStmt = if typeMapping.hasKey(node.protoType): quote do: `stream`.`protoRead`()
  else: quote do: `stream`.`protoRead`(`stream`.protoReadInt64()) #TODO: This is not implemented on the writer level

see protobuf failure

home/runner/work/Nim/Nim/pkgstemp/protobuf/src/protobuf.nim(786, 79) Error: attempting to call routine: 'protoRead'
    found 'protoRead' [let declared in /home/runner/work/Nim/Nim/pkgstemp/protobuf/src/protobuf.nim(785, 11)]

[haxscramper]

Closing because it seems like it is impossible to implement cleanly, considering all of these ridiculous edge cases that I didn't even know were valid. Basically allowing any kind of flexibility with block arguments would create 'danging else' kind of situation, turning implementation in a completely broken piece of garbage, and it is not worth it.

  readStmt = if 1: quote do: 3 # ok now
    else: quote do: 2

  readStmt = if 1: quote: 3 # ok now
    else: quote: 2

  match: # Supported now
    myOf: 12
  of:
    discard

  match 1: # supported now, would be ambigous to implement
    match 2:
    of 1: discard # For inner one, indented against 'match 2'
    of 1: discard # Meant to be added to outer, or inner?
  of 1: discard # Added to outer one

The same goes for match arg\nof - very ambiguous, current grammar is overly flexible, someone probably already depends on all edge cases that exist, and breaking their code for minor consistency improvements does not make any sense.

[haxscramper]

And this is off-topic, but what is the point of having CI that randomly allows passing invalid code in the first run? If I initially updated grammar, it could potentially be merged, because the implementation looks so "harmless" and "simple" and no sane person could make up code like this for unit tests.

[ringabout]

It was a mistake in testament logics and has been fixed.

see #18805

Because it didn't raise when a package name was wrong. The error was swallowed silently.

https://github.com/nim-lang/Nim/pull/18806/files