Normative: Always report assignment failure to canonical numeric string properties of immutable-backed TypedArray instances

Note that this includes non-integer-index but still canonical numeric
properties such as "-0", "-1", "1.2", and String(2**53) =
"9007199254740992", but does not include non-canonical-numeric
properties such as "1.20", "1e3", and "0x20".

Ideally, TypedArrays would restrict special treatment of canonical
numeric string properties to the strict subset that are integer indices
(aligning with similar treatment in String), but that is out of scope
for this commit.

Author: gibson042

spec.emu

@@ -131,8 +131,9 @@ contributors: Mark S. Miller, Richard Gibson
           1. If _P_ is a String, then
             1. Let _numericIndex_ be CanonicalNumericIndexString(_P_).
             1. If _numericIndex_ is not *undefined*, then
+              1. <ins>NOTE: TypedArray instances restrict own and inherited canonical numeric string properties to integer indices valid for their backing buffers, but assignment failures for canonical numeric string properties are only reported when the buffer is immutable.</ins>
+              1. <ins>If IsImmutableBuffer(_O_.[[ViewedArrayBuffer]]) is *true*, return *false*.</ins>
               1. If SameValue(_O_, _Receiver_) is *true*, then
-                1. <ins>IsValidIntegerIndex(_O_, _numericIndex_) is *true* and IsImmutableBuffer(_O_.[[ViewedArrayBuffer]]) is *true*, return *false*.</ins>
                 1. Perform ? TypedArraySetElement(_O_, _numericIndex_, _V_).
                 1. Return *true*.
               1. If IsValidIntegerIndex(_O_, _numericIndex_) is *false*, return *true*.
@@ -151,9 +152,10 @@ contributors: Mark S. Miller, Richard Gibson
         <dl class="header">
         </dl>
         <emu-alg>
+          1. <ins>Assert: IsImmutableBuffer(_O_.[[ViewedArrayBuffer]]) is *false*.</ins>
           1. If _O_.[[ContentType]] is ~bigint~, let _numValue_ be ? ToBigInt(_value_).
           1. Otherwise, let _numValue_ be ? ToNumber(_value_).
-          1. If IsValidIntegerIndex(_O_, _index_) is *true* <ins>and IsImmutableBuffer(_O_.[[ViewedArrayBuffer]]) is *false*</ins>, then
+          1. If IsValidIntegerIndex(_O_, _index_) is *true*, then
             1. Let _offset_ be _O_.[[ByteOffset]].
             1. Let _elementSize_ be TypedArrayElementSize(_O_).
             1. Let _byteIndexInBuffer_ be (ℝ(_index_) × _elementSize_) + _offset_.
@@ -162,7 +164,7 @@ contributors: Mark S. Miller, Richard Gibson
           1. Return ~unused~.
         </emu-alg>
         <emu-note>
-          <p>This operation always appears to succeed, but it has no effect when attempting to write past the end of a TypedArray or to a TypedArray which is backed by a detached <ins>or immutable</ins> ArrayBuffer.</p>
+          <p>This operation always appears to succeed, but it has no effect when attempting to write past the end of a TypedArray or to a TypedArray which is backed by a detached ArrayBuffer.</p>
         </emu-note>
       </emu-clause>
     </emu-clause>