Backport #100607 to 25.8.16: Re-add {database} macro support in clickhouse-client prompt

programs/client/Client.cpp

@@ -622,6 +622,18 @@ void Client::connect()
         boost::replace_all(prompt, "{" + key + "}", value);
 
     prompt = appendSmileyIfNeeded(prompt);
+
+    /// Sync the current database from the server after the handshake, but only when all
+    /// three conditions hold:
+    ///   - interactive: in batch mode the prompt is never displayed, so the extra
+    ///     round-trip to the server would add latency with no visible benefit;
+    ///   - no explicit --database flag: if the user passed --database, default_database
+    ///     is already set to the correct value and must not be overridden by whatever
+    ///     the server considers the current database;
+    ///   - {database} appears in the prompt string: querying the server is pointless
+    ///     when the macro is absent and the result would never be shown.
+    if (is_interactive && default_database.empty() && prompt.find("{database}") != String::npos)
+        syncDefaultDatabase();
 }
 
 // Prints changed settings to stderr. Useful for debugging fuzzing failures.

programs/client/clickhouse-client.xml

@@ -23,6 +23,7 @@
             {port}
             {user}
             {display_name}
+            {database}
 
         You can also use colored prompt, like in [1].
           [1]: https://misc.flogisoft.com/bash/tip_colors_and_formatting

src/Client/ClientBase.cpp

@@ -2916,7 +2916,9 @@ bool ClientBase::processQueryText(const String & text)
 
 String ClientBase::getPrompt() const
 {
-    return prompt;
+    String result = prompt;
+    boost::replace_all(result, "{database}", default_database.empty() ? "default" : default_database);
+    return result;
 }
 
 
@@ -3130,6 +3132,22 @@ std::string ClientBase::executeQueryForSingleString(const std::string & query)
     }
 }
 
+void ClientBase::syncDefaultDatabase()
+{
+    try
+    {
+        const auto db = executeQueryForSingleString("SELECT currentDatabase()");
+        if (!db.empty())
+            default_database = db;
+        else
+            LOG_WARNING(getLogger("ClientBase"), "syncDefaultDatabase: server returned empty result for SELECT currentDatabase()");
+    }
+    catch (...)
+    {
+        LOG_WARNING(getLogger("ClientBase"), "syncDefaultDatabase: failed to query current database from server: {}", getCurrentExceptionMessage(false));
+    }
+}
+
 bool ClientBase::checkAIProviderAcknowledgment()
 {
     // If API key came from environment and user hasn't acknowledged yet, ask for confirmation

src/Client/ClientBase.h

@@ -301,6 +301,11 @@ class ClientBase
 
     String appendSmileyIfNeeded(const String & prompt);
 
+    /// Query the server for the current database and update default_database.
+    /// Called after the connection handshake so that the prompt reflects the
+    /// server-side default when no --database flag was passed.
+    void syncDefaultDatabase();
+
     /// Should be one of the first, to be destroyed the last,
     /// since other members can use them.
     /// This holder may not be initialized in case if we run the client in the embedded mode (SSH).

tests/queries/0_stateless/04056_client_prompt_database.expect

@@ -0,0 +1,48 @@
+#!/usr/bin/expect -f
+
+# Test that {database} macro in the clickhouse-client prompt reflects the current database
+# and updates dynamically after USE statements.
+# https://github.com/ClickHouse/ClickHouse/issues/49118
+
+set basedir [file dirname $argv0]
+set basename [file tail $argv0]
+if {[info exists env(CLICKHOUSE_TMP)]} {
+    set CLICKHOUSE_TMP $env(CLICKHOUSE_TMP)
+} else {
+    set CLICKHOUSE_TMP "."
+}
+exp_internal -f $CLICKHOUSE_TMP/$basename.debuglog 0
+set history_file $CLICKHOUSE_TMP/$basename.history
+
+log_user 0
+set timeout 60
+match_max 100000
+
+expect_after {
+    # Do not ignore eof from expect
+    -i $any_spawn_id eof { exp_continue }
+    # A default timeout action is to do nothing, change it to fail
+    -i $any_spawn_id timeout { exit 1 }
+}
+
+# Test 1: {database} in prompt shows the database set via --database flag.
+# CLICKHOUSE_CLIENT_EXPECT_OPT includes --database=test (CLICKHOUSE_DATABASE).
+spawn bash -c "source $basedir/../shell_config.sh ; \$CLICKHOUSE_CLIENT_BINARY \$CLICKHOUSE_CLIENT_EXPECT_OPT --prompt '{database}' --history_file=$history_file"
+expect -re "\ntest :\\) $"
+
+# Test 2: {database} updates in the prompt after a USE statement.
+send -- "USE system;\r"
+expect "\nOk."
+expect -re "\nsystem :\\) $"
+
+send -- "\4"
+expect eof
+
+# Test 3: {database} shows the server's current database when --database flag is not passed.
+# syncDefaultDatabase() fires SELECT currentDatabase() after the handshake and writes
+# the result into default_database, so the prompt reflects the server-side default.
+spawn bash -c "source $basedir/../shell_config.sh ; opts=\$(echo \"\$CLICKHOUSE_CLIENT_EXPECT_OPT\" | sed 's/--database=\[^ \]*//g') ; \$CLICKHOUSE_CLIENT_BINARY \$opts --prompt '{database}' --history_file=$history_file"
+expect -re "\ndefault :\\) $"
+
+send -- "\4"
+expect eof

tests/queries/0_stateless/04057_local_prompt_database.expect

@@ -0,0 +1,40 @@
+#!/usr/bin/expect -f
+
+# Test that {database} macro in the clickhouse-local prompt reflects the current database
+# and updates dynamically after USE statements.
+# https://github.com/ClickHouse/ClickHouse/issues/49118
+
+set basedir [file dirname $argv0]
+set basename [file tail $argv0]
+if {[info exists env(CLICKHOUSE_TMP)]} {
+    set CLICKHOUSE_TMP $env(CLICKHOUSE_TMP)
+} else {
+    set CLICKHOUSE_TMP "."
+}
+exp_internal -f $CLICKHOUSE_TMP/$basename.debuglog 0
+set history_file $CLICKHOUSE_TMP/$basename.history
+
+log_user 0
+set timeout 60
+match_max 100000
+
+expect_after {
+    # Do not ignore eof from expect
+    -i $any_spawn_id eof { exp_continue }
+    # A default timeout action is to do nothing, change it to fail
+    -i $any_spawn_id timeout { exit 1 }
+}
+
+# Test 1: {database} in prompt shows "default" when --database flag is not passed.
+# default_database is empty in that case; getPrompt() falls back to the literal
+# string "default" so no server round-trip is needed.
+spawn bash -c "source $basedir/../shell_config.sh ; \$CLICKHOUSE_LOCAL --disable_suggestion --enable-progress-table-toggle=0 --prompt '{database}' --history_file=$history_file"
+expect -re "\ndefault :\\) $"
+
+# Test 2: {database} updates in the prompt after a USE statement.
+send -- "USE system;\r"
+expect "\nOk."
+expect -re "\nsystem :\\) $"
+
+send -- "\4"
+expect eof