add comment and tests

Author: aviatesk

base/views.jl

@@ -126,6 +126,9 @@ macro view(ex)
     Meta.isexpr(ex, :ref) || throw(ArgumentError(
         "Invalid use of @view macro: argument must be a reference expression A[...]."))
     ex = replace_ref_begin_end!(ex)
+    # NOTE We embed `view` as a function object itself directly into the AST.
+    #      By doing this, we prevent the creation of function definitions like
+    #      `view(A, idx) = xxx` in cases such as `@view(A[idx]) = xxx.`
     if Meta.isexpr(ex, :ref)
         ex = Expr(:call, view, ex.args...)
     elseif Meta.isexpr(ex, :let) && (arg2 = ex.args[2]; Meta.isexpr(arg2, :ref))

test/subarray.jl

@@ -937,3 +937,21 @@ end
     v = view(1:2, r)
     @test v == view(1:2, collect(r))
 end
+
+# https://github.com/JuliaLang/julia/pull/53064
+# `@view(A[idx]) = xxx` should raise syntax error always
+@test try
+    Core.eval(@__MODULE__, :(@view(A[idx]) = 2))
+    false
+catch err
+    err isa ErrorException && startswith(err.msg, "syntax:")
+end
+module Issue53064
+import Base: view
+end
+@test try
+    Core.eval(Issue53064, :(@view(A[idx]) = 2))
+    false
+catch err
+    err isa ErrorException && startswith(err.msg, "syntax:")
+end