Enclose grouping parentheses with parens node (#222)

Introduce a new kind `K"parens"` to represent grouping parentheses with
a tree node of their own. This makes it simple for tooling to process
and preserve parenthesized expressions without resorting to searching
through the attached syntax trivia.

An alternative considered here was to use `K"block"` with a single
child which would avoid introducing an extra kind of node. But in that
case we couldn't distinguish between a trivial block like `(a;)` vs bare
parentheses `(a)`. It also makes implementing `peek_behind` more
complicated.

Author: c42f

src/expr.jl

@@ -197,6 +197,9 @@ function _to_expr(node::SyntaxNode; iteration_spec=false, need_linenodes=true,
         end
     elseif headsym === :where
         reorder_parameters!(args, 2)
+    elseif headsym == :parens
+        # parens are used for grouping and don't appear in the Expr AST
+        return only(args)
     elseif headsym in (:try, :try_finally_catch)
         # Try children in source order:
         #   try_block catch_var catch_block else_block finally_block

src/parse_stream.jl

@@ -582,26 +582,25 @@ function first_child_position(stream::ParseStream, pos::ParseStreamPosition)
 end
 
 function peek_behind(stream::ParseStream; skip_trivia::Bool=true)
-    pos = position(stream)
-    if !skip_trivia || !token_is_last(stream, pos)
-        return peek_behind(stream, pos)
-    else
-        token_index = lastindex(stream.tokens)
-        range_index = lastindex(stream.ranges)
-        last_token_in_nonterminal = isempty(stream.ranges) ? 0 :
-                                    stream.ranges[range_index].last_token
-        while token_index > last_token_in_nonterminal
-            t = stream.tokens[token_index]
-            if !is_trivia(t) && kind(t) != K"TOMBSTONE"
-                break
-            end
-            token_index -= 1
-        end
-        if token_index > 0
-            return peek_behind(stream, ParseStreamPosition(token_index, range_index))
-        else
-            internal_error("Can't peek behind at start of stream")
+    token_index = lastindex(stream.tokens)
+    range_index = lastindex(stream.ranges)
+    while range_index >= firstindex(stream.ranges) &&
+            kind(stream.ranges[range_index]) == K"parens"
+        range_index -= 1
+    end
+    last_token_in_nonterminal = range_index == 0 ? 0 :
+                                stream.ranges[range_index].last_token
+    while token_index > last_token_in_nonterminal
+        t = stream.tokens[token_index]
+        if kind(t) != K"TOMBSTONE" && (!skip_trivia || !is_trivia(t))
+            break
         end
+        token_index -= 1
+    end
+    if token_index > 0
+        return peek_behind(stream, ParseStreamPosition(token_index, range_index))
+    else
+        internal_error("Can't peek behind at start of stream")
     end
 end
 

src/parser.jl

@@ -315,8 +315,8 @@ function was_eventually_call(ps::ParseState)
         b = peek_behind(stream, p)
         if b.kind == K"call"
             return true
-        elseif b.kind == K"where" || (b.kind == K"::" &&
-                                      has_flags(b.flags, INFIX_FLAG))
+        elseif b.kind == K"where" || b.kind == K"parens" ||
+                (b.kind == K"::" && has_flags(b.flags, INFIX_FLAG))
             p = first_child_position(ps, p)
         else
             return false
@@ -885,7 +885,7 @@ function parse_range(ps::ParseState)
             if had_newline
                 # Error message for people coming from python
                 # 1:\n2   ==> (call-i 1 : (error))
-                # (1:\n2) ==> (call-i 1 : 2)
+                # (1:\n2) ==> (parens (call-i 1 : 2))
                 emit_diagnostic(ps, whitespace=true,
                                 error="line break after `:` in range expression")
                 bump_invisible(ps, K"error")
@@ -1021,7 +1021,7 @@ function parse_unary_subtype(ps::ParseState)
         elseif k2 in KSet"{ ("
             # parse <:{T}(x::T) or <:(x::T) like other unary operators
             # <:{T}(x::T)  ==>  (call (curly <: T) (:: x T))
-            # <:(x::T)     ==>  (<:-pre (:: x T))
+            # <:(x::T)     ==>  (<:-pre (parens (:: x T)))
             parse_where(ps, parse_juxtapose)
         else
             # <: x          ==>  (<:-pre x)
@@ -1108,9 +1108,9 @@ end
 # Juxtoposition. Ugh! But so useful for units and Field identities like `im`
 #
 # 2x       ==>  (juxtapose 2 x)
-# 2(x)     ==>  (juxtapose 2 x)
-# (2)(3)x  ==>  (juxtapose 2 3 x)
-# (x-1)y   ==>  (juxtapose (call-i x - 1) y)
+# 2(x)     ==>  (juxtapose 2 (parens x))
+# (2)(3)x  ==>  (juxtapose (parens 2) (parens 3) x)
+# (x-1)y   ==>  (juxtapose (parens (call-i x - 1)) y)
 # x'y      ==>  (juxtapose (call-post x ') y)
 #
 # flisp: parse-juxtapose
@@ -1239,9 +1239,9 @@ function parse_unary(ps::ParseState)
 
         mark_before_paren = position(ps)
         bump(ps, TRIVIA_FLAG) # (
-        initial_semi = peek(ps) == K";"
+        _is_paren_call = peek(ps, skip_newlines=true) in KSet"; )"
         opts = parse_brackets(ps, K")") do had_commas, had_splat, num_semis, num_subexprs
-            is_paren_call = had_commas || had_splat || initial_semi
+            is_paren_call = had_commas || had_splat || _is_paren_call
             return (needs_parameters=is_paren_call,
                     is_paren_call=is_paren_call,
                     is_block=!is_paren_call && num_semis > 0)
@@ -1263,6 +1263,7 @@ function parse_unary(ps::ParseState)
             # +(a...)   ==>  (call + (... a))
             # +(a;b,c)  ==>  (call + a (parameters b c))
             # +(;a)     ==>  (call + (parameters a))
+            # +()       ==>  (call +)
             # Prefix calls have higher precedence than ^
             # +(a,b)^2  ==>  (call-i (call + a b) ^ 2)
             # +(a,b)(x)^2  ==>  (call-i (call (call + a b) x) ^ 2)
@@ -1292,21 +1293,23 @@ function parse_unary(ps::ParseState)
             parse_factor_with_initial_ex(ps, mark)
         else
             # Unary function calls with brackets as grouping, not an arglist
-            # .+(a)    ==>  (dotcall-pre (. +) a)
+            # .+(a)    ==>  (dotcall-pre (. +) (parens a))
             if opts.is_block
                 # +(a;b)   ==>  (call-pre + (block-p a b))
                 emit(ps, mark_before_paren, K"block", PARENS_FLAG)
+            else
+                emit(ps, mark_before_paren, K"parens")
             end
             # Not a prefix operator call but a block; `=` is not `kw`
-            # +(a=1)  ==>  (call-pre + (= a 1))
+            # +(a=1)  ==>  (call-pre + (parens (= a 1)))
             # Unary operators have lower precedence than ^
-            # +(a)^2  ==>  (call-pre + (call-i a ^ 2))
-            # .+(a)^2  ==>  (dotcall-pre + (call-i a ^ 2))
-            # +(a)(x,y)^2  ==>  (call-pre + (call-i (call a x y) ^ 2))
+            # +(a)^2  ==>  (call-pre + (call-i (parens a) ^ 2))
+            # .+(a)^2  ==>  (dotcall-pre + (call-i (parens a) ^ 2))
+            # +(a)(x,y)^2  ==>  (call-pre + (call-i (call (parens a) x y) ^ 2))
             parse_call_chain(ps, mark_before_paren)
             parse_factor_with_initial_ex(ps, mark_before_paren)
             if is_type_operator(op_t)
-                # <:(a)  ==>  (<:-pre a)
+                # <:(a)  ==>  (<:-pre (parens a))
                 emit(ps, mark, op_k, PREFIX_OP_FLAG)
                 reset_node!(ps, op_pos, flags=TRIVIA_FLAG)
             else
@@ -1451,7 +1454,7 @@ function parse_identifier_or_interpolate(ps::ParseState)
     mark = position(ps)
     parse_unary_prefix(ps)
     b = peek_behind(ps)
-    # export (x::T) ==> (export (error (::-i x T)))
+    # export (x::T) ==> (export (error (parens (::-i x T))))
     # export outer  ==> (export outer)
     # export ($f)   ==> (export ($ f))
     ok = (b.is_leaf  && (b.kind == K"Identifier" || is_operator(b.kind))) ||
@@ -1491,13 +1494,13 @@ function parse_call_chain(ps::ParseState, mark, is_macrocall=false)
         k = kind(t)
         if !is_macrocall && ps.space_sensitive && preceding_whitespace(t) &&
                 k in KSet"( [ { \" \"\"\" ` ```"
-            # [f (x)]  ==>  (hcat f x)
+            # [f (x)]  ==>  (hcat f (parens x))
             # [f x]    ==>  (hcat f x)
             break
         elseif is_macrocall && (preceding_whitespace(t) || !(k in KSet"( [ { ' ."))
             # Macro calls with space-separated arguments
             # @foo a b    ==> (macrocall @foo a b)
-            # @foo (x)    ==> (macrocall @foo x)
+            # @foo (x)    ==> (macrocall @foo (parens x))
             # @foo (x,y)  ==> (macrocall @foo (tuple-p x y))
             # [@foo x]    ==> (vect (macrocall @foo x))
             # [@foo]      ==> (vect (macrocall @foo))
@@ -1537,8 +1540,8 @@ function parse_call_chain(ps::ParseState, mark, is_macrocall=false)
             # f(a,b)  ==>  (call f a b)
             # f(a=1; b=2) ==> (call f (= a 1) (parameters (= b 2)))
             # f(a; b; c)  ==> (call f a (parameters b) (parameters c))
-            # (a=1)()  ==>  (call (= a 1))
-            # f (a)  ==>  (call f (error-t) a b)
+            # (a=1)()  ==>  (call (parens (= a 1)))
+            # f (a)    ==>  (call f (error-t) a)
             bump_disallowed_space(ps)
             bump(ps, TRIVIA_FLAG)
             parse_call_arglist(ps, K")")
@@ -1580,7 +1583,8 @@ function parse_call_chain(ps::ParseState, mark, is_macrocall=false)
             else
                 # a[i]    ==>  (ref a i)
                 # a[i,j]  ==>  (ref a i j)
-                # (a=1)[] ==>  (ref (= a 1))
+                # (a=1)[] ==>  (ref (parens (= a 1)))
+                # a[end]  ==>  (ref a end)
                 # T[x   y]  ==>  (typed_hcat T x y)
                 # T[x ; y]  ==>  (typed_vcat T x y)
                 # T[a b; c d]  ==>  (typed_vcat T (row a b) (row c d))
@@ -1905,7 +1909,7 @@ function parse_resword(ps::ParseState)
         else
             # Function/macro definition with no methods
             # function f end       ==> (function f)
-            # (function f \n end)  ==> (function f)
+            # (function f \n end)  ==> (parens (function f))
             # function f \n\n end  ==> (function f)
             # function $f end      ==> (function ($ f))
             # macro f end          ==> (macro f)
@@ -2007,7 +2011,7 @@ function parse_resword(ps::ParseState)
         # export a, \n @b  ==>  (export a @b)
         # export +, ==     ==>  (export + ==)
         # export \n a      ==>  (export a)
-        # export \$a, \$(a*b) ==> (export (\$ a) (\$ (call-i a * b)))
+        # export \$a, \$(a*b) ==> (export (\$ a) (\$ (parens (call-i a * b))))
         bump(ps, TRIVIA_FLAG)
         parse_comma_separated(ps, parse_atsym)
         emit(ps, mark, K"export")
@@ -2105,10 +2109,10 @@ function parse_function_signature(ps::ParseState, is_function::Bool)
             emit(ps, mark, K"error", error="Invalid macro name")
         else
             # macro f()     end  ==>  (macro (call f) (block))
-            # macro (:)(ex) end  ==>  (macro (call : ex) (block))
-            # macro (type)(ex) end  ==>  (macro (call type ex) (block))
+            # macro (:)(ex) end  ==>  (macro (call (parens :) ex) (block))
+            # macro (type)(ex) end  ==>  (macro (call (parens type) ex) (block))
             # macro $f()    end  ==>  (macro (call ($ f)) (block))
-            # macro ($f)()  end  ==>  (macro (call ($ f)) (block))
+            # macro ($f)()  end  ==>  (macro (call (parens ($ f))) (block))
         end
     else
         if peek(ps) == K"("
@@ -2145,10 +2149,11 @@ function parse_function_signature(ps::ParseState, is_function::Bool)
                 # function ()(x) end  ==> (function (call (tuple-p) x) (block))
                 emit(ps, mark, K"tuple", PARENS_FLAG)
             else
-                # function (A).f() end  ==> (function (call (. A (quote f))) (block))
-                # function (:)() end    ==> (function (call :) (block))
-                # function (x::T)() end ==> (function (call (::-i x T)) (block))
-                # function (::T)() end  ==> (function (call (::-pre T)) (block))
+                # function (A).f() end  ==> (function (call (. (parens A) (quote f))) (block))
+                # function (:)() end    ==> (function (call (parens :)) (block))
+                # function (x::T)() end ==> (function (call (parens (::-i x T))) (block))
+                # function (::T)() end  ==> (function (call (parens (::-pre T))) (block))
+                emit(ps, mark, K"parens", PARENS_FLAG)
             end
         else
             parse_unary_prefix(ps)
@@ -2163,8 +2168,7 @@ function parse_function_signature(ps::ParseState, is_function::Bool)
                 # function type() end  ==>  (function (call type) (block))
                 # function \n f() end  ==>  (function (call f) (block))
                 # function $f() end    ==>  (function (call ($ f)) (block))
-                # function (:)() end  ==>  (function (call :) (block))
-                # function (::Type{T})(x) end ==> (function (call (::-pre (curly Type T)) x) (block))
+                # function (::Type{T})(x) end ==> (function (call (parens (::-pre (curly Type T))) x) (block))
             end
         end
     end
@@ -2205,8 +2209,8 @@ function parse_function_signature(ps::ParseState, is_function::Bool)
     # function (f() where T) end         ==> (function (where (call f) T) (block))
     # function (f()) where T end         ==> (function (where (call f) T) (block))
     # function (f() where T) where U end ==> (function (where (where (call f) T) U) (block))
-    # function (f()::S) end              ==> (function (::-i (call f) S) (block))
-    # function ((f()::S) where T) end    ==> (function (where (::-i (call f) S) T) (block))
+    # function (f()::S) end              ==> (function (parens (::-i (call f) S)) (block))
+    # function ((f()::S) where T) end    ==> (function (where (parens (::-i (call f) S)) T) (block))
     #
     # TODO: Warn for use of parens? The precedence of `::` and
     # `where` don't work inside parens so this is a bit of a syntax
@@ -2401,7 +2405,7 @@ function parse_atsym(ps::ParseState)
     else
         # export a  ==>  (export a)
         # export \n a  ==>  (export a)
-        # export $a, $(a*b)  ==>  (export ($ a) ($ (call * a b)))
+        # export $a, $(a*b)  ==>  (export ($ a) (parens ($ (call * a b))))
         parse_identifier_or_interpolate(ps)
     end
 end
@@ -2706,7 +2710,7 @@ end
 function parse_generator(ps::ParseState, mark, flatten=false)
     t = peek_token(ps)
     if !preceding_whitespace(t)
-        # [(x)for x in xs]  ==>  (comprehension (generator x (error) (= x xs)))
+        # [(x)for x in xs]  ==>  (comprehension (generator (parens x) (error) (= x xs)))
         bump_invisible(ps, K"error", TRIVIA_FLAG,
                        error="Expected space before `for` in generator")
     end
@@ -2715,21 +2719,21 @@ function parse_generator(ps::ParseState, mark, flatten=false)
     filter_mark = position(ps)
     parse_comma_separated(ps, parse_iteration_spec)
     if peek(ps) == K"if"
-        # (a for x in xs if cond) ==> (generator a (filter (= x xs) cond))
+        # (a for x in xs if cond) ==> (parens (generator a (filter (= x xs) cond)))
         bump(ps, TRIVIA_FLAG)
         parse_cond(ps)
         emit(ps, filter_mark, K"filter")
     end
     t = peek_token(ps)
     if kind(t) == K"for"
-        # (xy for x in xs for y in ys)  ==> (flatten xy (= x xs) (= y ys))
-        # (xy for x in xs for y in ys for z in zs)  ==> (flatten xy (= x xs) (= y ys) (= z zs))
+        # (xy for x in xs for y in ys)  ==> (parens (flatten xy (= x xs) (= y ys)))
+        # (xy for x in xs for y in ys for z in zs)  ==> (parens (flatten xy (= x xs) (= y ys) (= z zs)))
         parse_generator(ps, mark, true)
         if !flatten
             emit(ps, mark, K"flatten")
         end
     elseif !flatten
-        # (x for a in as)  ==>  (generator x (= a as))
+        # (x for a in as)  ==>  (parens (generator x (= a as)))
         emit(ps, mark, K"generator")
     end
 end
@@ -3071,10 +3075,11 @@ function parse_paren(ps::ParseState, check_identifiers=true)
             emit(ps, mark, K"block", PARENS_FLAG)
         else
             # Parentheses used for grouping
-            # (a * b)     ==>  (call-i * a b)
-            # (a=1)       ==>  (= a 1)
-            # (x)         ==>  x
-            # (a...)      ==>  (... a)
+            # (a * b)     ==>  (parens (call-i * a b))
+            # (a=1)       ==>  (parens (= a 1))
+            # (x)         ==>  (parens x)
+            # (a...)      ==>  (parens (... a))
+            emit(ps, mark, K"parens")
         end
     end
 end
@@ -3144,8 +3149,8 @@ function parse_brackets(after_parse::Function,
                 continue
             elseif k == K"for"
                 # Generator syntax
-                # (x for a in as)       ==>  (generator x (= a as))
-                # (x \n\n for a in as)  ==>  (generator x (= a as))
+                # (x for a in as)       ==>  (parens (generator x (= a as)))
+                # (x \n\n for a in as)  ==>  (parens (generator x (= a as)))
                 parse_generator(ps, mark)
             else
                 # Error - recovery done when consuming closing_kind
@@ -3203,8 +3208,8 @@ function parse_string(ps::ParseState, raw::Bool)
             bump(ps, TRIVIA_FLAG)
             k = peek(ps)
             if k == K"("
-                # "a $(x + y) b"  ==>  (string "a " (call-i x + y) " b")
-                # "hi$("ho")"     ==>  (string "hi" (string "ho"))
+                # "a $(x + y) b"  ==>  (string "a " (parens (call-i x + y)) " b")
+                # "hi$("ho")"     ==>  (string "hi" (parens (string "ho")))
                 parse_atom(ps)
             elseif k == K"var"
                 # var identifiers disabled in strings
@@ -3346,7 +3351,7 @@ function parse_string(ps::ParseState, raw::Bool)
     end
     # String interpolations
     # "$x$y$z"  ==> (string x y z)
-    # "$(x)"    ==> (string x)
+    # "$(x)"    ==> (string (parens x))
     # "$x"      ==> (string x)
     # """$x"""  ==> (string-s x)
     #
@@ -3440,7 +3445,7 @@ function parse_atom(ps::ParseState, check_identifiers=true)
             # Being inside quote makes keywords into identifiers at the
             # first level of nesting
             # :end ==> (quote end)
-            # :(end) ==> (quote (error (end)))
+            # :(end) ==> (quote (parens (error-t)))
             # Being inside quote makes end non-special again (issue #27690)
             # a[:(end)]  ==>  (ref a (quote (error-t end)))
             parse_atom(ParseState(ps, end_symbol=false), false)