Bug 1609264 - Don't populate _lastConsoleInputEvaluation when doing an eager evaluation. r=bhackett.

This was messing up with the $_ command.
A webconsole test case is added to ensure this
works as expected now.

Differential Revision: https://phabricator.services.mozilla.com/D59990

--HG--
extra : moz-landing-system : lando

devtools/client/webconsole/test/browser/browser_jsterm_eager_evaluation.js

@@ -25,6 +25,14 @@ add_task(async function() {
   await pushPref(EAGER_EVALUATION_PREF, true);
   const hud = await openNewTabAndConsole(TEST_URI);
 
+  // Do an evaluation to populate $_
+  await executeAndWaitForMessage(
+    hud,
+    "'result: ' + (x + y)",
+    "result: 7",
+    ".result"
+  );
+
   setInputValue(hud, "x + y");
   await waitForEagerEvaluationResult(hud, "7");
 
@@ -72,6 +80,13 @@ add_task(async function() {
 
   setInputValue(hud, "Math.round(3.2)");
   await waitForEagerEvaluationResult(hud, "3");
+
+  info("Check that $_ wasn't polluted by eager evaluations");
+  setInputValue(hud, "$_");
+  await waitForEagerEvaluationResult(hud, `"result: 7"`);
+
+  setInputValue(hud, "'> ' + $_");
+  await waitForEagerEvaluationResult(hud, `"> result: 7"`);
 });
 
 // Test that the currently selected autocomplete result is eagerly evaluated.

devtools/server/actors/webconsole.js

@@ -1298,16 +1298,20 @@ const WebConsoleActor = ActorClassWithSpec(webconsoleSpec, {
       }
     }
 
-    if (!awaitResult) {
-      this._lastConsoleInputEvaluation = result;
-    } else {
-      // If we evaluated a top-level await expression, we want to assign its result to the
-      // _lastConsoleInputEvaluation only when the promise resolves, and only if it
-      // resolves. If the promise rejects, we don't re-assign _lastConsoleInputEvaluation,
-      // it will keep its previous value.
-      awaitResult.then(res => {
-        this._lastConsoleInputEvaluation = this.makeDebuggeeValue(res);
-      });
+    // Don't update _lastConsoleInputEvaluation in eager evaluation, as it would interfere
+    // with the $_ command.
+    if (!request.eager) {
+      if (!awaitResult) {
+        this._lastConsoleInputEvaluation = result;
+      } else {
+        // If we evaluated a top-level await expression, we want to assign its result to the
+        // _lastConsoleInputEvaluation only when the promise resolves, and only if it
+        // resolves. If the promise rejects, we don't re-assign _lastConsoleInputEvaluation,
+        // it will keep its previous value.
+        awaitResult.then(res => {
+          this._lastConsoleInputEvaluation = this.makeDebuggeeValue(res);
+        });
+      }
     }
 
     return {