Disallow more than three consecutive newlines (2 empty lines)

README.md

@@ -164,6 +164,7 @@ julia-master --project -m Runic --check --diff "${files[@]}"
 
 This is a list of things that Runic currently is doing:
 
+ - [Line width limit](#line-width-limit)
  - [Indentation](#indentation)
  - [Spaces around operators, assignment, etc](#spaces-around-operators-assignment-etc)
  - [Spaces around keywords](#spaces-around-keywords)
@@ -172,7 +173,7 @@ This is a list of things that Runic currently is doing:
  - [Literal floating point numbers](#literal-floating-point-numbers)
  - [Literal hex and oct numbers](#literal-hex-and-oct-numbers)
  - [Parentheses around operator calls in colon](#parentheses-around-operator-calls-in-colon)
- - [`in` instead of `∈` and `=`]()#in-instead-of--and-
+ - [`in` instead of `∈` and `=`](#in-instead-of--and-)
  - [Braces around right hand side of `where`](#braces-around-right-hand-side-of-where)
  - [Trailing whitespace](#trailing-whitespace)
 
@@ -256,6 +257,26 @@ x = a + b *
     d
 ```
 
+### Vertical spacing
+
+Runic removes empty vertical spacing so that there are at maximum two empty lines between
+expressions. Examples:
+```diff
+-function f()
+-     x = 1
+-
+-
+-
+-    return x
+-end
++function f()
++     x = 1
++
++
++    return x
++end
+```
+
 ### Spaces around operators, assignment, etc
 
 Runic formats spaces around infix operators, assignments, comparison chains, and type

src/Runic.jl

@@ -299,6 +299,7 @@ function format_node!(ctx::Context, node::Node)::Union{Node, Nothing, NullNode}
     ctx.call_depth += 1
     @return_something insert_delete_mark_newlines(ctx, node)
     @return_something trim_trailing_whitespace(ctx, node)
+    @return_something max_three_consecutive_newlines(ctx, node)
     @return_something format_hex_literals(ctx, node)
     @return_something format_oct_literals(ctx, node)
     @return_something format_float_literals(ctx, node)

src/runestone.jl

@@ -1312,6 +1312,31 @@ function parens_around_op_calls_in_colon(ctx::Context, node::Node)
     end
 end
 
+
+# Remove more than two newlines in a row
+function max_three_consecutive_newlines(ctx::Context, node::Node)
+    is_leaf(node) && return nothing
+    kids = verified_kids(node)
+    idx = findfirst(x -> kind(x) === K"NewlineWs", kids)
+    while idx !== nothing
+        if idx + 3 <= length(kids) &&
+                (kind(kids[idx + 1]) == kind(kids[idx + 2]) == kind(kids[idx + 3]) == K"NewlineWs")
+            kids′ = Vector{Node}(undef, length(kids) - 1)
+            for (i, kid) in pairs(kids)
+                if i == idx
+                    replace_bytes!(ctx, "", span(kids[idx]))
+                else
+                    accept_node!(ctx, kid)
+                    kids′[i < idx ? i : (i - 1)] = kid
+                end
+            end
+            return make_node(node, kids′)
+        end
+        idx = findnext(x -> kind(x) === K"NewlineWs", kids, idx + 1)
+    end
+    return nothing
+end
+
 # This function materialized all indentations marked by `insert_delete_mark_newlines`.
 function four_space_indent(ctx::Context, node::Node)
     kind(node) === K"NewlineWs" || return nothing

test/runtests.jl

@@ -722,3 +722,16 @@ end
             "$(o)\n    a, # a\n    b,\n$(c)"
     end
 end
+
+@testset "max three consecutive newlines" begin
+    f, g = "f() = 1", "g() = 2"
+    for n in 1:5
+        nl = "\n"
+        m = min(n, 3)
+        @test format_string(f * nl^n * g) == f * nl^m * g
+        @test format_string("module A" * nl^n * "end") == "module A" * nl^m * "end"
+        @test format_string("function f()" * nl^n * "end") == "function f()" * nl^m * "end"
+        @test format_string("function f()" * nl^2 * "x = 1" * nl^n * "end") ==
+            "function f()" * nl^2 * "    x = 1" * nl^m * "end"
+    end
+end