From f6a5f87128bcd8932e610fa6484b7889d1607d5c Mon Sep 17 00:00:00 2001
From: Shuhei Kadowaki <aviatesk@gmail.com>
Date: Fri, 26 Jan 2024 16:24:13 +0900
Subject: [PATCH 1/2] remove unnecessary `true &&` part from `at-view` macro

The modification that expands `@view A[i]` to `true && view(A, i)`
appears to go back as far as #20247. However, I'm not entirely sure why
this is necessary. Considering that just expanding it to `view(A, i)`
still seems to pass the base test suite, I wonder if it might be
just better to get rid of that part.
---
 base/views.jl | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/base/views.jl b/base/views.jl
index d83005c86f46c..0792c10088302 100644
--- a/base/views.jl
+++ b/base/views.jl
@@ -123,20 +123,18 @@ julia> A
 ```
 """
 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)
     if Meta.isexpr(ex, :ref)
-        ex = replace_ref_begin_end!(ex)
-        if Meta.isexpr(ex, :ref)
-            ex = Expr(:call, view, ex.args...)
-        else # ex replaced by let ...; foo[...]; end
-            if !(Meta.isexpr(ex, :let) && Meta.isexpr(ex.args[2], :ref))
-                error("invalid expression")
-            end
-            ex.args[2] = Expr(:call, view, ex.args[2].args...)
-        end
-        Expr(:&&, true, esc(ex))
+        ex = Expr(:call, view, ex.args...)
+    elseif Meta.isexpr(ex, :let) && (arg2 = ex.args[2]; Meta.isexpr(arg2, :ref))
+        # ex replaced by let ...; foo[...]; end
+        ex.args[2] = Expr(:call, view, arg2.args...)
     else
-        throw(ArgumentError("Invalid use of @view macro: argument must be a reference expression A[...]."))
+        error("invalid expression")
     end
+    return esc(ex)
 end
 
 ############################################################################

From 63ee5209162f0567beb7ca548fa2785a2d02bba0 Mon Sep 17 00:00:00 2001
From: Shuhei Kadowaki <aviatesk@gmail.com>
Date: Sat, 27 Jan 2024 13:13:51 +0900
Subject: [PATCH 2/2] add comment and tests

---
 base/views.jl    |  3 +++
 test/subarray.jl | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/base/views.jl b/base/views.jl
index 0792c10088302..6898abdda1471 100644
--- a/base/views.jl
+++ b/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))
diff --git a/test/subarray.jl b/test/subarray.jl
index ad68496e38245..40877d842df76 100644
--- a/test/subarray.jl
+++ b/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