Parse arr[end] differently from arr[var"end"]

Author: mlechu

src/expr.jl

@@ -76,6 +76,10 @@ function _leaf_to_Expr(source, txtbuf, txtbuf_offset, head, srcrange, node)
         return k == K"error" ?
             Expr(:error) :
             Expr(:error, "$(_token_error_descriptions[k]): `$(source[srcrange])`")
+    elseif k == K"RefBegin"
+        return Expr(:begin)
+    elseif k == K"RefEnd"
+        return Expr(:end)
     else
         val = isnothing(node) ?
             parse_julia_literal(txtbuf, head, srcrange .+ txtbuf_offset) :

src/kinds.jl

@@ -198,6 +198,10 @@ register_kinds!(JuliaSyntax, 0, [
         # macro name may not appear as characters in the source: The `@` may be
         # detached from the macro name as in `@A.x` (ugh!!), or have a _str or _cmd
         # suffix appended.
+        "BEGIN_REF_IDENTIFIERS"
+            "RefBegin"
+            "RefEnd"
+        "BEGIN_REF_IDENTIFIERS"
         "BEGIN_MACRO_NAMES"
             "MacroName"
             "StringMacroName"

src/parser.jl

@@ -15,7 +15,7 @@ struct ParseState
     space_sensitive::Bool
     # Seeing `for` stops parsing macro arguments and makes a generator
     for_generator::Bool
-    # Treat 'end' like a normal symbol instead of a reserved word
+    # Treat begin/end like special symbols instead of reserved words
     end_symbol::Bool
     # Treat newline like ordinary whitespace instead of as a potential separator
     whitespace_newline::Bool
@@ -3627,6 +3627,14 @@ function parse_atom(ps::ParseState, check_identifiers=true, has_unary_prefix=fal
         elseif check_identifiers && is_closing_token(ps, leading_kind)
             # :(end)  ==>  (quote-: (error end))
             bump(ps, error="invalid identifier")
+        elseif ps.end_symbol && leading_kind in KSet"begin end"
+            # https://github.com/JuliaLang/julia/issues/57269
+            # Parse a[begin] differently from a[var"begin"]
+            if leading_kind == K"begin"
+                bump(ps, remap_kind=K"RefBegin")
+            elseif leading_kind == K"end"
+                bump(ps, remap_kind=K"RefEnd")
+            end
         else
             # Remap keywords to identifiers.
             # :end  ==>  (quote-: end)