Allow any of ≔ ⩴ ≕ as identifiers (#478)

These assignment-precedence operators shouldn't be special syntax and
should instead be usable as normal identifiers just like `~`.

Also add more test cases for the true syntactic operators.

Fixes #405

Author: c42f

src/kinds.jl

@@ -298,6 +298,7 @@ register_kinds!(JuliaSyntax, 0, [
 
     # Level 1
     "BEGIN_ASSIGNMENTS"
+        "BEGIN_SYNTACTIC_ASSIGNMENTS"
         "="
         "+="
         "-="   # Also used for "−="
@@ -314,9 +315,10 @@ register_kinds!(JuliaSyntax, 0, [
         "\\="
         "&="
         ":="
-        "~"
         "\$="
         "⊻="
+        "END_SYNTACTIC_ASSIGNMENTS"
+        "~"
         "≔"
         "⩴"
         "≕"
@@ -1227,6 +1229,7 @@ is_prec_pipe_lt(x)     = kind(x) == K"<|"
 is_prec_pipe_gt(x)     = kind(x) == K"|>"
 is_syntax_kind(x)      = K"BEGIN_SYNTAX_KINDS"<= kind(x) <= K"END_SYNTAX_KINDS"
 is_macro_name(x)       = K"BEGIN_MACRO_NAMES" <= kind(x) <= K"END_MACRO_NAMES"
+is_syntactic_assignment(x) = K"BEGIN_SYNTACTIC_ASSIGNMENTS" <= kind(x) <= K"END_SYNTACTIC_ASSIGNMENTS"
 
 function is_number(x)
     kind(x) in (K"Integer", K"BinInt", K"HexInt", K"OctInt", K"Float", K"Float32")

src/parser.jl

@@ -279,7 +279,7 @@ function is_syntactic_operator(k)
     # TODO: Do we need to disallow dotted and suffixed forms here?
     # The lexer itself usually disallows such tokens, so it's not clear whether
     # we need to handle them. (Though note `.->` is a token...)
-    return k in KSet"&& || . ... ->" || (is_prec_assignment(k) && k != K"~")
+    return k in KSet"&& || . ... ->" || is_syntactic_assignment(k)
 end
 
 function is_syntactic_unary_op(k)
@@ -617,7 +617,8 @@ function parse_assignment_with_initial_ex(ps::ParseState, mark, down::T) where {
             # [a ~b]  ==>  (hcat a (call-pre ~ b))
             return
         end
-        # ~ is the only non-syntactic assignment-precedence operator.
+        # ~ is currently the only assignment-precedence operator which is parsed as a call.
+        # TODO: Make the other non-syntactic assignments such as `≔ ⩴ ≕` into calls as well?
         # a ~ b      ==>  (call-i a ~ b)
         # a .~ b     ==>  (dotcall-i a ~ b)
         # [a ~ b c]  ==>  (hcat (call-i a ~ b) c)

test/parser.jl

@@ -763,12 +763,36 @@ tests = [
         """var"x"1"""   =>  "(var x (error-t))"
         """var"x"y"""   =>  "(var x (error-t))"
         # Standalone syntactic operators are errors
-        "+="  =>  "(error +=)"
         "?"   =>  "(error ?)"
+        "&&"  =>  "(error &&)"
+        "||"  =>  "(error ||)"
+        "."   =>  "(error .)"
+        "..." =>  "(error ...)"
+        "+="  =>  "(error +=)"
+        "-="  =>  "(error -=)"
+        "*="  =>  "(error *=)"
+        "/="  =>  "(error /=)"
+        "//=" =>  "(error //=)"
+        "|="  =>  "(error |=)"
+        "^="  =>  "(error ^=)"
+        "÷="  =>  "(error ÷=)"
+        "%="  =>  "(error %=)"
+        "<<=" =>  "(error <<=)"
+        ">>=" =>  "(error >>=)"
+        ">>>="=>  "(error >>>=)"
+        "\\=" =>  "(error \\=)"
+        "&="  =>  "(error &=)"
+        ":="  =>  "(error :=)"
+        "\$=" =>  "(error \$=)"
+        "⊻="  =>  "(error ⊻=)"
         ".+=" =>  "(error (. +=))"
         # Normal operators
         "+"  =>  "+"
+        # Assignment-precedence operators which can be used as identifiers
         "~"  =>  "~"
+        "≔"  =>  "≔"
+        "⩴"  =>  "⩴"
+        "≕"  =>  "≕"
         # Quoted syntactic operators allowed
         ":+="  =>  "(quote-: +=)"
         ":.="  =>  "(quote-: (. =))"
@@ -777,7 +801,7 @@ tests = [
         ":end" => "(quote-: end)"
         ":(end)" => "(quote-: (parens (error-t)))"
         ":<:"  => "(quote-: <:)"
-        # unexpect =
+        # unexpected =
         "="    => "(error =)"
         # parse_cat
         "[]"        =>  "(vect)"