Replace all calls to db_set_active, which is deprecated.

#2 looks good.
another instance of "db_set_active()" is present in following File: Kindly add this to #2 as well.
core/lib/Drupal/Core/Database/Install/Tasks.php:159

Thanks!

call to db_set_active in core/lib/Drupal/Core/Database/Install/Tasks.php:159 also changed with new syntax.

Minor Code standards issue. Else it looks good.

index 40a589c..7628a40 100644
--- a/core/lib/Drupal/Core/Database/Driver/mysql/Install/Tasks.php

--- a/core/lib/Drupal/Core/Database/Driver/mysql/Install/Tasks.php
+++ b/core/lib/Drupal/Core/Database/Driver/mysql/Install/Tasks.php

+++ b/core/lib/Drupal/Core/Database/Driver/mysql/Install/Tasks.php
@@ -59,7 +59,7 @@ public function minimumVersion() {

@@ -59,7 +59,7 @@ public function minimumVersion() {
   protected function connect() {
     try {
       // This doesn't actually test the connection.
-      db_set_active();
+       \Drupal\Core\Database\Database::setActiveConnection();
       // Now actually do a check.

--- a/core/lib/Drupal/Core/Database/Driver/pgsql/Install/Tasks.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Install/Tasks.php

+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Install/Tasks.php
@@ -58,7 +58,7 @@ public function minimumVersion() {

@@ -58,7 +58,7 @@ public function minimumVersion() {
   protected function connect() {
     try {
       // This doesn't actually test the connection.
-      db_set_active();
+       \Drupal\Core\Database\Database::setActiveConnection();
       // Now actually do a check.

+++ b/core/lib/Drupal/Core/Database/Driver/sqlite/Install/Tasks.php
@@ -54,7 +54,7 @@ public function getFormOptions(array $database) {

@@ -54,7 +54,7 @@ public function getFormOptions(array $database) {
   protected function connect() {
     try {
       // This doesn't actually test the connection.
-      db_set_active();
+       \Drupal\Core\Database\Database::setActiveConnection();
       // Now actually do a check.

Minor correction :
\Drupal\Core... lines are having an extra space before the code.

Kindly correct these as well. Thanks !!

Line spaces corrected.

Patch #10 Looks good.
Thanks !

The meta issue reads: "...replace all usages of the function (except tests for the function itself)...". LoggingTest is the only test calling db_set_active(), it's not exactly specifically testing the global function but as it's the only test, I'm not sure what we want.

In my opinion we should replace LoggingTest instance also.
Replace full namespace call, as namespace is already in use statement.

Patch #15 still applying. Tested on 8.6.x.
Looks good

This patch should add an @trigger_error() to db_set_active() so people can discover they need to replace the calls. See https://www.drupal.org/core/deprecation
This will also prove we've replaced all the usages in core.

fixed as per #19

+++ b/core/includes/database.inc
@@ -335,6 +335,10 @@ function db_transaction($name = NULL, array $options = []) {
+  @trigger_error('db_set_active() is deprecated in Drupal 8.0.x and will be
+  removed before Drupal 9.0.0. Use
+  \Drupal\Core\Database\Database::setActiveConnection() instead.
+  https://www.drupal.org/project/drupal/issues/2848812.', E_USER_DEPRECATED);

The message should all be on one line otherwise it won't flow right when displayed in logs etc...

Also it would nice to add a test of the db_set_active() function to \Drupal\KernelTests\Core\Database\RegressionTest(). You'll need to add @group legacy and @expectedDeprecation deprecation message to the new test.

change recored - https://www.drupal.org/node/2944084
fixed as per #21

1. +++ b/core/includes/database.inc
   @@ -335,6 +335,7 @@ function db_transaction($name = NULL, array $options = []) {
   +  @trigger_error('db_set_active() is deprecated in Drupal 8.0.x and will be removed before Drupal 9.0.0. Use \Drupal\Core\Database\Database::setActiveConnection() instead.https://www.drupal.org/node/2944084.', E_USER_DEPRECATED);
   

   This should end with ... instead. See https://www.drupal.org/node/2944084.

2. +++ b/core/tests/Drupal/KernelTests/Core/Database/RegressionTest.php
   @@ -57,4 +57,16 @@ public function testDBIndexExists() {
   +    $this->assertSame(TRUE, db_set_active(), 'Returns true for active connection.');
   +    $this->assertSame(FALSE, db_set_active(), 'Returns false for non-active connection.');
   

   The docs are

      * @return string|null
      *   The previous database connection key.
      */
     final public static function setActiveConnection($key = 'default') {
   

   So I can't see how this works.

improved the test

+++ b/core/tests/Drupal/KernelTests/Core/Database/LoggingTest.php
@@ -113,11 +113,11 @@ public function testEnableMultiConnectionLogging() {
     $queries1 = Database::getLog('testing1');

+++ b/core/tests/Drupal/KernelTests/Core/Database/RegressionTest.php
@@ -57,4 +59,16 @@ public function testDBIndexExists() {
+    $this->assertTrue(db_set_active($get_active_db), 'Database connection is active');

This method returns the key. Let's assert against that rather than truthiness.

Addressed the #25 comment on updated patch & also added an interdiff.

Looks good for me

Committed/pushed to 8.6.x, thanks!

Great!!. I hope other issues like these will be pushed as well.

#31 +1
There are alot issues like this (db_* replacements) that should be synchronized after each commit.
So If some of the other issues are RTBC it would be great to review and commit to saving the time to track changes at the related issues.
Anyway, thanks)