Fix #2957, make empty selections report an error

Previously they were creating empty data: URLs and causing server rejection

addon/webextension/background/senderror.js

@@ -37,6 +37,9 @@ this.senderror = (function() {
     MY_SHOTS: {
       title: browser.i18n.getMessage("selfScreenshotErrorTitle")
     },
+    EMPTY_SELECTION: {
+      title: browser.i18n.getMessage("emptySelectionErrorTitle")
+    },
     generic: {
       title: browser.i18n.getMessage("genericErrorTitle"),
       info: browser.i18n.getMessage("genericErrorDetails"),
@@ -112,7 +115,9 @@ this.senderror = (function() {
     if (!errorObj.noPopup) {
       exports.showError(errorObj);
     }
-    exports.reportError(errorObj);
+    if (!errorObj.noReport) {
+      exports.reportError(errorObj);
+    }
   });
 
   return exports;

addon/webextension/selector/shooter.js

@@ -67,6 +67,14 @@ this.shooter = (function() { // eslint-disable-line no-unused-vars
     // isSaving indicates we're aleady in the middle of saving
     // we use a timeout so in the case of a failure the button will
     // still start working again
+    if (Math.floor(selectedPos.left) == Math.floor(selectedPos.right) ||
+        Math.floor(selectedPos.top) == Math.floor(selectedPos.bottom)) {
+        let exc = new Error("Empty selection");
+        exc.popupMessage = "EMPTY_SELECTION";
+        exc.noReport = true;
+        catcher.unhandled(exc);
+        return;
+    }
     const uicontrol = global.uicontrol;
     let deactivateAfterFinish = true;
     if (isSaving) {

docs/error-handling.md

@@ -105,3 +105,5 @@ Note that any information will be serialized as JSON.  Specifically `undefined`
 If you add `exc.popupMessage = "Something happened"` then that detail will be added.  Be careful about localization here.
 
 Add `exc.noPopup = true` if you don't want the user notified about the error (but the error will still be sent to Sentry).
+
+Add `exc.noReport = true` if you don't want the error reported to Sentry.

locales/en-US/webextension.properties

@@ -27,6 +27,8 @@ loginErrorDetails = We couldn’t save your shot because there is a problem with
 unshootablePageErrorTitle = We can’t screenshot this page.
 unshootablePageErrorDetails = This isn’t a standard Web page, so you can’t take a screenshot of it.
 selfScreenshotErrorTitle = You can’t take a shot of a Firefox Screenshots page!
+# Fired when someone makes a zero-width or zero-height selection
+emptySelectionErrorTitle = Your selection is too small
 genericErrorTitle = Whoa! Firefox Screenshots went haywire.
 genericErrorDetails = We’re not sure what just happened. Care to try again or take a shot of a different page?
 # Section for onboarding strings