Allow K"error" when parsing to SyntaxTree (JuliaLang#60327)

I had assumed a valid parse since parse errors would detonate in lowering
anyway, but that was wrong: JETLS uses `ignore_errors=true` in parsing to
SyntaxTree. I plan to make some larger changes where I'll make sure
`RawGreenNode->SyntaxTree` is more thoroughly tested, but this is a
quick fix to get JETLS working.

Author: mlechu

JuliaLowering/src/syntax_graph.jl

@@ -877,12 +877,10 @@ function _green_to_ast(parent::Kind, ex::SyntaxTree; eq_to_kw=false)
         makenode(graph, ex, ex, _map_green_to_ast(k, children(ex); eq_to_kw))
     elseif k === K"parens"
         cs = _map_green_to_ast(parent, children(ex); eq_to_kw)
-        @assert length(cs) === 1
-        cs[1]
+        length(cs) === 1 ? cs[1] : makenode(graph, ex, ex, cs)
     elseif k in KSet"var char"
         cs = _map_green_to_ast(parent, children(ex))
-        @assert length(cs) === 1
-        cs[1]
+        length(cs) === 1 ? cs[1] : makenode(graph, ex, ex, cs)
     elseif k === K"=" && eq_to_kw
         setattr!(makenode(graph, ex, ex, _map_green_to_ast(k, children(ex))),
                  :kind, K"kw")
@@ -894,8 +892,11 @@ function _green_to_ast(parent::Kind, ex::SyntaxTree; eq_to_kw=false)
         # M.@x parses to (. M (macro_name x))
         # @M.x parses to (macro_name (. M x))
         # We want (. M @x) (both identifiers) in either case
-        @assert numchildren(ex) === 2 && kind(ex[1]) === K"@"
-        id = ex[2]
+        cs = _map_green_to_ast(k, children(ex))
+        if length(cs) !== 1 || !(kind(cs[1]) in KSet". Identifier")
+            return makenode(graph, ex, ex, cs)
+        end
+        id = cs[1]
         mname_raw = (kind(id) === K"." ? id[2] : id).name_val
         mac_id = setattr!(makeleaf(graph, ex, K"Identifier"), :name_val,
                           lower_identifier_name(mname_raw, K"macro_name"))

JuliaLowering/test/syntax_graph.jl

@@ -45,6 +45,13 @@ end
     @test Expr(parsestmt(SyntaxTree, "begin a + b ; c end", filename="none")) ==
         Meta.parse("begin a + b ; c end")
 
+    # Parsing to SyntaxTree: errors should fall through
+    @test parsestmt(SyntaxTree, "@"; ignore_errors=true) isa SyntaxTree
+    @test parsestmt(SyntaxTree, "@@@"; ignore_errors=true) isa SyntaxTree
+    @test parsestmt(SyntaxTree, "(a b c)"; ignore_errors=true) isa SyntaxTree
+    @test parsestmt(SyntaxTree, "'a b c'"; ignore_errors=true) isa SyntaxTree
+
+    # @SyntaxTree
     tree1 = JuliaLowering.@SyntaxTree :(some_unique_identifier)
     @test tree1 isa SyntaxTree
     @test kind(tree1) == K"Identifier"