Fix <: and >: without LHS

This patch fixes formatting of <: and >: when used without LHS. This is
again an inconsistency compared to other operators.

TODO.md

@@ -0,0 +1,24 @@
+# TODOs, notes, and various thoughts
+
+## Inconsistencies
+
+- The `spaces_around_operators` rule have the following inconsistencies.
+
+   - `:`, `^`, and `::` instead fall under `no_spaces_around_colon_etc`:
+     ```julia
+     # current formatting      # "consistent" formatting
+     a:b                       a : b                            ✖
+     a^b                       a ^ b                            ✖
+     a::b                      a :: b                           ✖
+     ```
+
+   - `<:` and `<:` fall under `no_spaces_around_colon_etc` if they have no LHS:
+     ```julia
+     # current formatting      # "consistent" formatting
+     a <: b                    a <: b                           ✔
+     a >: b                    a >: b                           ✔
+     a{c <: b}                 a{c <: b}                        ✔
+     a{c >: b}                 a{c >: b}                        ✔
+     a{<:b}                    a{<: b}                          ✖
+     a{>:b}                    a{>: b}                          ✖
+     ```

src/chisels.jl

@@ -49,6 +49,11 @@ function first_leaf(node::JuliaSyntax.GreenNode)
     end
 end
 
+# Return number of non-whitespace children
+function n_children(node::JuliaSyntax.GreenNode)
+    return is_leaf(node) ? 0 : count(!JuliaSyntax.is_whitespace, verified_children(node))
+end
+
 # This function exist so that we can type-assert the return value to narrow it down from
 # `Union{Tuple{}, Vector{JuliaSyntax.GreenNode}}` to `Vector{JuliaSyntax.GreenNode}`. Must
 # only be called after verifying that the node has children.

src/runestone.jl

@@ -271,7 +271,7 @@ end
 function spaces_around_operators(ctx::Context, node::JuliaSyntax.GreenNode)
     if !(
         (is_infix_op_call(node) && !(JuliaSyntax.kind(infix_op_call_op(node)) in KSet": ^")) ||
-        (JuliaSyntax.kind(node) in KSet"<: >:" && !is_leaf(node)) ||
+        (JuliaSyntax.kind(node) in KSet"<: >:" && n_children(node) == 3) ||
         (JuliaSyntax.kind(node) === K"comparison" && !JuliaSyntax.is_trivia(node))
     )
         return nothing
@@ -308,9 +308,9 @@ function no_spaces_around_x(ctx::Context, node::JuliaSyntax.GreenNode, is_x::F)
 
     looking_for_x = false
 
-    # K"::" is a special case here since it can be used without an LHS in e.g. function
-    # definitions like `f(::Int) = ...`.
-    if JuliaSyntax.kind(node) === K"::"
+    # K"::", K"<:", and K">:" are special cases here since they can be used without an LHS
+    # in e.g. `f(::Int) = ...` and `Vector{<:Real}`.
+    if JuliaSyntax.kind(node) in KSet":: <: >:"
         looking_for_x = is_x(first_non_whitespace_child(node))::Bool
     end
 
@@ -354,11 +354,12 @@ end
 function no_spaces_around_colon_etc(ctx::Context, node::JuliaSyntax.GreenNode)
     if !(
         (is_infix_op_call(node) && JuliaSyntax.kind(infix_op_call_op(node)) in KSet": ^") ||
-        (JuliaSyntax.kind(node) === K"::" && !is_leaf(node))
+        (JuliaSyntax.kind(node) === K"::" && !is_leaf(node)) ||
+        (JuliaSyntax.kind(node) in KSet"<: >:" && n_children(node) == 2)
     )
         return nothing
     end
-    @assert JuliaSyntax.kind(node) in KSet"call ::"
-    is_x = x -> is_leaf(x) && JuliaSyntax.kind(x) in KSet": ^ ::"
+    @assert JuliaSyntax.kind(node) in KSet"call :: <: >:"
+    is_x = x -> is_leaf(x) && JuliaSyntax.kind(x) in KSet": ^ :: <: >:"
     return no_spaces_around_x(ctx, node, is_x)
 end

test/runtests.jl

@@ -187,17 +187,23 @@ end
 end
 
 @testset "whitespace around <: and >:, no whitespace around ::" begin
-    # K"::"
+    # K"::" with both LHS and RHS
     @test format_string("a::T") == "a::T"
     @test format_string("a::T::S") == "a::T::S"
     @test format_string("a  ::  T") == "a::T"
+    # K"::" with just RHS
     @test format_string("f(::T)::T = 1") == "f(::T)::T = 1"
     @test format_string("f(:: T) :: T = 1") == "f(::T)::T = 1"
-    # K"<:" and K">:"
+    # K"<:" and K">:" with both LHS and RHS
     @test format_string("a<:T") == "a <: T"
     @test format_string("a>:T") == "a >: T"
     @test format_string("a  <:   T") == "a <: T"
     @test format_string("a  >:   T") == "a >: T"
+    # K"<:" and K">:" with just RHS
+    @test format_string("V{<:T}") == "V{<:T}"
+    @test format_string("V{<: T}") == "V{<:T}"
+    @test format_string("V{>:T}") == "V{>:T}"
+    @test format_string("V{>: T}") == "V{>:T}"
     # K"comparison" for chains
     @test format_string("a<:T<:S") == "a <: T <: S"
     @test format_string("a>:T>:S") == "a >: T >: S"