if-statement optional braces when single statement

TODO.md

@@ -242,8 +242,16 @@
     c :: b + 3     # c is constrained to `i32`
     ```
 
-16. for if statements, allow `if (cond) one-line statement` or `if some_func(some_arg) one-line statement` (instead of forcing either `if (cond) { block }` or `if cond { block }`)
+16. for if statements, allow `if (cond) one-line statement` or `if some_func(some_arg) one-line statement` (instead of forcing either `if (cond) { block }` or `if cond { block }`) (implemented)
   - if statements without a bracketed body must wrap the condition in parentheses UNLESS it's a function call
+  - brace-less single-statement bodies apply to the then-body, the `else`-body, and the
+    unwrap/guard forms (`if v |x| stmt`); each branch is independent, so braced and
+    brace-less branches mix freely
+  - the parenthesize-or-call rule constrains only the then-branch condition; `else` and the
+    unwrap `|...|` already delimit, so they need no parentheses
+  - the brace-less statement may sit on the line after the condition
+  - parser-only change (`parse_branch_body` in `compiler/parser/parser.odin`): a brace-less
+    body is just a 1-element statement slice, so the checker and codegen are unchanged
 
 17. add slice-by-range
   - allow the use of a range in slice expressions: