Keep track of previous/next sibling

Sometimes there is a need to check the kind (possibly more) of previous
and next siblings in order to decide on formatting. This patch keeps
track of this in the Context.

This is used for replacing trailing whitespace from consecutive
NewlineWs nodes since sometimes the whitespace is after the LF.

src/Runic.jl

@@ -23,6 +23,11 @@ mutable struct Context
     # User settings
     verbose::Bool
     debug::Bool
+    # Current state
+    # node::Union{JuliaSyntax.GreenNode, Nothing}
+    prev_sibling::Union{JuliaSyntax.GreenNode, Nothing}
+    next_sibling::Union{JuliaSyntax.GreenNode, Nothing}
+    # parent::Union{JuliaSyntax.GreenNode, Nothing}
 end
 
 function Context(src_str; debug::Bool = false, verbose::Bool = debug)
@@ -30,7 +35,15 @@ function Context(src_str; debug::Bool = false, verbose::Bool = debug)
     src_tree = JuliaSyntax.parseall(JuliaSyntax.GreenNode, src_str; ignore_warnings=true)
     fmt_io = IOBuffer()
     fmt_tree = nothing
-    return Context(src_str, src_tree, src_io, fmt_io, fmt_tree, verbose, debug)
+    return Context(
+        src_str, src_tree, src_io, fmt_io, fmt_tree, verbose, debug,
+        nothing, nothing,
+    )
+end
+
+function next_sibling_kind(ctx::Context)::Union{JuliaSyntax.Kind, Nothing}
+    next = ctx.next_sibling
+    return next === nothing ? nothing : JuliaSyntax.kind(next)
 end
 
 # Read the bytes of the current node from the output io
@@ -66,16 +79,24 @@ function format_node_with_children!(ctx::Context, node::JuliaSyntax.GreenNode)
     if !JuliaSyntax.haschildren(node)
         return node
     end
+    # Keep track of the siblings on this stack
+    prev_sibling = ctx.prev_sibling
+    next_sibling = ctx.next_sibling
+    ctx.prev_sibling = nothing
+    ctx.next_sibling = nothing
     # @assert JuliaSyntax.haschildren(node)
     span_sum = 0
     original_bytes = node_bytes(ctx, node) # TODO: Read into reusable buffer
     children = JuliaSyntax.children(node)
     # The new node parts
     head′ = JuliaSyntax.head(node)
-    children′ = ()
+    children′ = children # This aliases until the need to copy below
     # Keep track of changes; if no child changes the original node can be returned
     any_child_changed = false
     for (i, child) in pairs(children)
+        # Set the siblings: previous from children′, next from children
+        ctx.prev_sibling = get(children′, i - 1, nothing)
+        ctx.next_sibling = get(children, i + 1, nothing)
         child′ = child
         span_sum += JuliaSyntax.span(child)
         this_child_changed = false
@@ -86,6 +107,8 @@ function format_node_with_children!(ctx::Context, node::JuliaSyntax.GreenNode)
             child′′ = format_node!(ctx, child′)
             if child′′ === nullnode
                 this_child_changed = true
+                # TODO: When this is fixed the sibling setting above needs to handle this
+                # too
                 error("TODO: handle removed children")
             elseif child′′ === child′
                 child′ = child′′
@@ -113,13 +136,17 @@ function format_node_with_children!(ctx::Context, node::JuliaSyntax.GreenNode)
         end
         any_child_changed |= this_child_changed
         if any_child_changed
-            # Promote children from tuple to array and copy older siblings into it
+            # De-alias the children if needed
-            if children′ === ()
+            if children′ === children
                 children′ = eltype(children)[children[j] for j in 1:(i-1)]
             end
             push!(children′, child′)
         end
     end
+    # Reset the siblings
+    ctx.prev_sibling = prev_sibling
+    ctx.next_sibling = next_sibling
+    # Return a new node if any of the children changed
     if any_child_changed
         span′ = mapreduce(JuliaSyntax.span, +, children′; init=0)
         return JuliaSyntax.GreenNode(head′, span′, children′)
@@ -137,6 +164,12 @@ function format_node!(ctx::Context, node::JuliaSyntax.GreenNode)
         @assert !JuliaSyntax.haschildren(node)
         str = String(node_bytes(ctx, node))
         str′ = replace(str, r"\h*(\r\n|\r|\n)" => '\n')
+        # If the next sibling is also a NewlineWs we can trim trailing
+        # whitespace from this node too
+        next_kind = next_sibling_kind(ctx)
+        if next_kind === K"NewlineWs"
+            str′ = replace(str′, r"(\r\n|\r|\n)\h*" => '\n')
+        end
         if str != str′
             # Write new bytes and reset the stream
             nb = write_and_reset(ctx, str′)
@@ -393,7 +426,7 @@ function format_tree!(ctx::Context)
     # Reset IOs so that the offsets are correct
     seek(ctx.src_io, src_pos)
     seek(ctx.fmt_io, fmt_pos)
-    # Keep track of the depth to break out of infinite loops
+    # Set the root to the current node
     root′ = root
     itr = 0
     while true

test/runtests.jl

@@ -10,7 +10,7 @@ using Test:
     println(io, "  ") # Trailing space on consecutive lines
     println(io, "  ")
     str = String(take!(io))
-    @test_broken format_string(str) == "a = 1\nb = 2\n\n\n"
+    @test format_string(str) == "a = 1\nb = 2\n\n\n"
 end
 
 @testset "Hex/oct/bin literal integers" begin