Compat for odd Exprs in long form anonymous functions (#6)

The following construct is parsed oddly by the reference parser with the
tuple omitted from the argument list. Add a compatibility hack for that
during Expr conversion.

    function (xs...)
        body
    end

With this we now have compatible parsing for all of the stdlib for Julia
1.6 and 1.7, so turn on this test by default in those cases.

Author: c42f

README.md

@@ -546,6 +546,10 @@ parsing `key=val` pairs inside parentheses.
   or (b) all lines should be dedented only one character, as that's the
   matching prefix.
 
+* Parsing of anonymous function arguments is somewhat inconsistent.
+  `function (xs...) \n body end` parses the argument list as `(... xs)`, whereas
+  `function (x) \n body end` parses the argument list as `(tuple x)`.
+
 # Comparisons to other packages
 
 ### Official Julia compiler

src/syntax_tree.jl

@@ -415,6 +415,16 @@ function _to_expr(node::SyntaxNode, iteration_spec=false)
             # Add block for source locations
             args[2] = Expr(:block, loc, args[2])
         end
+    elseif headsym == :function
+        if length(args) > 1 && Meta.isexpr(args[1], :tuple)
+            # Convert to weird Expr forms for long-form anonymous functions.
+            #
+            # (function (tuple (... xs)) body) ==> (function (... xs) body)
+            if length(args[1].args) == 1 && Meta.isexpr(args[1].args[1], :...)
+                # function (xs...) \n body end
+                args[1] = args[1].args[1]
+            end
+        end
     end
     if headsym == :inert || (headsym == :quote && length(args) == 1 &&
                  !(a1 = only(args); a1 isa Expr || a1 isa QuoteNode ||

test/parse_packages.jl

@@ -20,8 +20,9 @@ base_tests_path = joinpath(Sys.BINDIR, Base.DATAROOTDIR, "julia", "test")
 end
 
 end
-if haskey(ENV, "PARSE_STDLIB")
-# TODO: Turn on by default
+
+if VERSION < v"1.8-DEV" || haskey(ENV, "PARSE_STDLIB")
+# TODO: Fix on 1.8
 
 @testset "Parse Julia stdlib at $(Sys.STDLIB)" begin
     for stdlib in readdir(Sys.STDLIB)

test/syntax_tree.jl

@@ -24,4 +24,11 @@
                  Expr(:(=), Expr(:call, :f), :xs),
                  Expr(:block))
     end
+
+    @testset "Long form anonymous functions" begin
+        @test parseall(Expr, "function (xs...)\nbody end", rule=:statement) ==
+            Expr(:function,
+                 Expr(:..., :xs),
+                 Expr(:block, :body))
+    end
 end