Normative: Define module root level context (#98)

Co-authored-by: Andreu Botella <abotella@igalia.com>

Author: legendecas

spec.html

@@ -305,6 +305,60 @@ <h1>Runtime Semantics: Evaluation</h1>
   </emu-clause>
 </emu-clause>
 
+<emu-clause id="sec-ecmascript-language-scripts-and-modules">
+  <h1>ECMAScript Language: Scripts and Modules</h1>
+
+  <emu-clause id="sec-modules">
+    <h1>Modules</h1>
+
+    <emu-clause id="sec-module-semantics">
+      <h1>Module Semantics</h1>
+
+      <emu-clause id="sec-source-text-module-records">
+        <h1>Source Text Module Records</h1>
+        <emu-clause id="sec-source-text-module-record-execute-module" type="concrete method">
+          <h1>
+            ExecuteModule (
+              optional _capability_: a PromiseCapability Record,
+            ): either a normal completion containing ~unused~ or a throw completion
+          </h1>
+          <dl class="header">
+            <dt>for</dt>
+            <dd>a Source Text Module Record _module_</dd>
+          </dl>
+
+          <emu-alg>
+            1. Let _moduleContext_ be a new ECMAScript code execution context.
+            1. Set the Function of _moduleContext_ to *null*.
+            1. Set the Realm of _moduleContext_ to _module_.[[Realm]].
+            1. Set the ScriptOrModule of _moduleContext_ to _module_.
+            1. Assert: _module_ has been linked and declarations in its module environment have been instantiated.
+            1. Set the VariableEnvironment of _moduleContext_ to _module_.[[Environment]].
+            1. Set the LexicalEnvironment of _moduleContext_ to _module_.[[Environment]].
+            1. Suspend the running execution context.
+            1. <ins>Let _moduleContextMapping_ be a new empty list.</ins>
+            1. <ins>Let _previousContextMapping_ be AsyncContextSwap(_moduleContextMapping_).</ins>
+            1. If _module_.[[HasTLA]] is *false*, then
+              1. Assert: _capability_ is not present.
+              1. Push _moduleContext_ onto the execution context stack; _moduleContext_ is now the running execution context.
+              1. Let _result_ be Completion(Evaluation of _module_.[[ECMAScriptCode]]).
+              1. Suspend _moduleContext_ and remove it from the execution context stack.
+              1. Resume the context that is now on the top of the execution context stack as the running execution context.
+              1. <ins>AsyncContextSwap(_previousContextMapping_).</ins>
+              1. If _result_ is an abrupt completion, then
+                1. Return ? _result_.
+            1. Else,
+              1. Assert: _capability_ is a PromiseCapability Record.
+              1. Perform AsyncBlockStart(_capability_, _module_.[[ECMAScriptCode]], _moduleContext_).
+              1. <ins>AsyncContextSwap(_previousContextMapping_).</ins>
+            1. Return ~unused~.
+          </emu-alg>
+        </emu-clause>
+      </emu-clause>
+    </emu-clause>
+  </emu-clause>
+</emu-clause>
+
 <emu-clause id="sec-control-abstraction-objects">
   <h1>Control Abstraction Objects</h1>