AST: Rearrange do to sit inside call/macrocall

`do` syntax is represented in `Expr` with the `do` outside the call.
This makes some sense syntactically (do appears as "an operator" after
the function call).

However semantically this nesting is awkward because the lambda
represented by the do block is passed to the call. This same problem
occurs for the macro form `@f(x) do \n body end` where the macro
expander needs a special rule to expand nestings of the form
`Expr(:do, Expr(:macrocall ...), ...)`, rearranging the expression which
are passed to this macro call rather than passing the expressions up the
tree.

In this PR, we change the parsing of

    @f(x, y) do a, b\n body\n end
    f(x, y) do a, b\n body\n end

to tack the `do` onto the end of the call argument list:

    (macrocall @f x y (do (tuple a b) body))
    (call f x y (do (tuple a b) body))

This achieves the following desirable properties
1. Content of `do` is nested inside the call which improves the match
   between AST and semantics
2. Macro can be passed the syntax as-is rather than the macro expander
   rearranging syntax before passing it to the macro
3. In the future, a macro can detect when it's being passed do syntax
   rather than lambda syntax
4. `do` head is used uniformly for both call and macrocall
5. We preserve the source ordering properties we need for the green tree.

Author: c42f

src/expr.jl

@@ -184,6 +184,16 @@ function _fixup_Expr_children!(head, loc, args)
     return args
 end
 
+# Remove the `do` block from the final position in a function/macro call arg list
+function _extract_do_lambda!(args)
+    if length(args) > 1 && Meta.isexpr(args[end], :do_lambda)
+        do_ex = pop!(args)::Expr
+        return Expr(:->, do_ex.args...)
+    else
+        return nothing
+    end
+end
+
 # Convert internal node of the JuliaSyntax parse tree to an Expr
 function _internal_node_to_Expr(source, srcrange, head, childranges, childheads, args)
     k = kind(head)
@@ -217,8 +227,12 @@ function _internal_node_to_Expr(source, srcrange, head, childranges, childheads,
             end
         end
     elseif k == K"macrocall"
+        do_lambda = _extract_do_lambda!(args)
         _reorder_parameters!(args, 2)
         insert!(args, 2, loc)
+        if do_lambda isa Expr
+            return Expr(:do, Expr(headsym, args...), do_lambda)
+        end
     elseif k == K"block" || (k == K"toplevel" && !has_flags(head, TOPLEVEL_SEMICOLONS_FLAG))
         if isempty(args)
             push!(args, loc)
@@ -247,6 +261,7 @@ function _internal_node_to_Expr(source, srcrange, head, childranges, childheads,
             popfirst!(args)
             headsym = Symbol("'")
         end
+        do_lambda = _extract_do_lambda!(args)
         # Move parameters blocks to args[2]
         _reorder_parameters!(args, 2)
         if headsym === :dotcall
@@ -259,6 +274,9 @@ function _internal_node_to_Expr(source, srcrange, head, childranges, childheads,
                 args[1] = Symbol(".", args[1])
             end
         end
+        if do_lambda isa Expr
+            return Expr(:do, Expr(headsym, args...), do_lambda)
+        end
     elseif k == K"." && length(args) == 1 && is_operator(childheads[1])
         # Hack: Here we preserve the head of the operator to determine whether
         # we need to coalesce it with the dot into a single symbol later on.
@@ -396,8 +414,8 @@ function _internal_node_to_Expr(source, srcrange, head, childranges, childheads,
             return QuoteNode(a1)
         end
     elseif k == K"do"
-        @check length(args) == 3
-        return Expr(:do, args[1], Expr(:->, args[2], args[3]))
+        # Temporary head which is picked up by _extract_do_lambda
+        headsym = :do_lambda
     elseif k == K"let"
         a1 = args[1]
         if @isexpr(a1, :block)

src/parser.jl

@@ -1510,12 +1510,12 @@ function parse_call_chain(ps::ParseState, mark, is_macrocall=false)
             bump_disallowed_space(ps)
             bump(ps, TRIVIA_FLAG)
             parse_call_arglist(ps, K")")
-            emit(ps, mark, is_macrocall ? K"macrocall" : K"call",
-                 is_macrocall ? PARENS_FLAG : EMPTY_FLAGS)
             if peek(ps) == K"do"
-                # f(x) do y body end  ==>  (do (call f x) (tuple y) (block body))
-                parse_do(ps, mark)
+                # f(x) do y body end  ==>  (call f x (do (tuple y) (block body)))
+                parse_do(ps)
             end
+            emit(ps, mark, is_macrocall ? K"macrocall" : K"call",
+                 is_macrocall ? PARENS_FLAG : EMPTY_FLAGS)
             if is_macrocall
                 # @x(a, b)   ==>  (macrocall-p @x a b)
                 # A.@x(y)    ==>  (macrocall-p (. A (quote @x)) y)
@@ -2274,18 +2274,19 @@ function parse_catch(ps::ParseState)
 end
 
 # flisp: parse-do
-function parse_do(ps::ParseState, mark)
+function parse_do(ps::ParseState)
+    mark = position(ps)
     bump(ps, TRIVIA_FLAG) # do
     ps = normal_context(ps)
     m = position(ps)
     if peek(ps) in KSet"NewlineWs ;"
-        # f() do\nend        ==>  (do (call f) (tuple) (block))
-        # f() do ; body end  ==>  (do (call f) (tuple) (block body))
+        # f() do\nend        ==>  (call f (do (tuple) (block)))
+        # f() do ; body end  ==>  (call f (do (tuple) (block body)))
         # this trivia needs to go into the tuple due to the way position()
         # works.
         bump(ps, TRIVIA_FLAG)
     else
-        # f() do x, y\n body end  ==>  (do (call f) (tuple x y) (block body))
+        # f() do x, y\n body end  ==>  (call f (do (tuple x y) (block body)))
         parse_comma_separated(ps, parse_range)
     end
     emit(ps, m, K"tuple")

test/expr.jl

@@ -299,11 +299,39 @@
 
     @testset "do block conversion" begin
         @test parsestmt("f(x) do y\n body end") ==
-            Expr(:do, Expr(:call, :f, :x),
+            Expr(:do,
+                 Expr(:call, :f, :x),
                  Expr(:->, Expr(:tuple, :y),
                       Expr(:block,
                            LineNumberNode(2),
                            :body)))
+
+        @test parsestmt("@f(x) do y body end") ==
+            Expr(:do,
+                 Expr(:macrocall, Symbol("@f"), LineNumberNode(1), :x),
+                 Expr(:->, Expr(:tuple, :y),
+                      Expr(:block,
+                           LineNumberNode(1),
+                           :body)))
+
+        @test parsestmt("f(x; a=1) do y body end") ==
+            Expr(:do,
+                 Expr(:call, :f, Expr(:parameters, Expr(:kw, :a, 1)), :x),
+                 Expr(:->, Expr(:tuple, :y),
+                      Expr(:block,
+                           LineNumberNode(1),
+                           :body)))
+
+        # Test calls with do inside them
+        @test parsestmt("g(f(x) do y\n body end)") ==
+            Expr(:call,
+                 :g,
+                 Expr(:do,
+                      Expr(:call, :f, :x),
+                      Expr(:->, Expr(:tuple, :y),
+                           Expr(:block,
+                                LineNumberNode(2),
+                                :body))))
     end
 
     @testset "= to Expr(:kw) conversion" begin

test/parser.jl

@@ -355,10 +355,11 @@ tests = [
         "A.@x(y)"    =>  "(macrocall-p (. A (quote @x)) y)"
         "A.@x(y).z"  =>  "(. (macrocall-p (. A (quote @x)) y) (quote z))"
         # do
-        "f() do\nend"         =>  "(do (call f) (tuple) (block))"
-        "f() do ; body end"   =>  "(do (call f) (tuple) (block body))"
-        "f() do x, y\n body end"  =>  "(do (call f) (tuple x y) (block body))"
-        "f(x) do y body end"  =>  "(do (call f x) (tuple y) (block body))"
+        "f() do\nend"         =>  "(call f (do (tuple) (block)))"
+        "f() do ; body end"   =>  "(call f (do (tuple) (block body)))"
+        "f() do x, y\n body end"  =>  "(call f (do (tuple x y) (block body)))"
+        "f(x) do y body end"  =>  "(call f x (do (tuple y) (block body)))"
+        "@f(x) do y body end" =>  "(macrocall-p @f x (do (tuple y) (block body)))"
 
         # square brackets
         "@S[a,b]"  => "(macrocall @S (vect a b))"