Handle \c in the interactive SQL shell

go/cmd/dolt/commands/sql.go

@@ -719,6 +719,9 @@ func execShell(sqlCtx *sql.Context, qryist cli.Queryist, format engine.PrintResu
 	}
 
 	verticalOutputLineTerminators := []string{"\\g", "\\G"}
+	// clearStatementTerminator mirrors the MySQL client's `\c` escape: it discards the statement
+	// currently being entered (however many lines it spans) without executing it.
+	clearStatementTerminator := "\\c"
 	backSlashCommands := make([]string, 0, len(slashCmds))
 	for _, cmd := range slashCmds {
 		backSlashCommands = append(backSlashCommands, "\\"+cmd.Name())
@@ -730,7 +733,7 @@ func execShell(sqlCtx *sql.Context, qryist cli.Queryist, format engine.PrintResu
 			"quit", "exit", "quit()", "exit()",
 		},
 		LineTerminator:     ";",
-		SpecialTerminators: verticalOutputLineTerminators,
+		SpecialTerminators: append(append([]string{}, verticalOutputLineTerminators...), clearStatementTerminator),
 		BackSlashCmds:      backSlashCommands,
 	}
 
@@ -783,6 +786,16 @@ func execShell(sqlCtx *sql.Context, qryist cli.Queryist, format engine.PrintResu
 			return
 		}
 
+		// \c cancels the statement currently being entered, matching the MySQL client. The buffered
+		// input is discarded without being executed or recorded in history, and the shell resets to
+		// a fresh prompt.
+		if strings.HasSuffix(query, clearStatementTerminator) {
+			nextPrompt, multiPrompt := postCommandUpdate(sqlCtx, qryist)
+			shell.SetPrompt(nextPrompt)
+			shell.SetMultiPrompt(multiPrompt)
+			return
+		}
+
 		trackHistory(shell, query)
 
 		query = strings.TrimSuffix(query, shell.LineTerminator())

integration-tests/bats/sql-shell-clear-statement.expect

@@ -0,0 +1,26 @@
+#!/usr/bin/expect
+
+set timeout 5
+set env(NO_COLOR) 1
+
+source  "$env(BATS_CWD)/helper/common_expect_functions.tcl"
+
+spawn dolt sql
+
+# \c cancels the statement currently being entered, mirroring the MySQL client's \c escape.
+# The buffered statement should be discarded without being executed. If \c were left
+# unhandled, the shell would fold it into the next line typed, producing a syntax error near
+# the stray backslash instead of running "select 1;" on its own -- see the bats assertions in
+# sql-shell.bats for how this is verified against the full transcript.
+expect_with_defaults {dolt-repo-[0-9]+/main\*?> } { send "select * from nonexistent_table \\c\r" }
+
+# Give the shell a moment to process (or mis-process) the \c before sending the next
+# statement, rather than racing to match a pattern that could also appear in echoed input.
+sleep 1
+
+send "select 1;\r"
+sleep 1
+
+send "quit\r"
+
+expect eof

integration-tests/bats/sql-shell.bats

@@ -155,6 +155,23 @@ teardown() {
     [ "$status" -eq 0 ]
 }
 
+# Regression coverage for https://github.com/dolthub/dolt/issues/10867
+# bats test_tags=no_lambda
+@test "sql-shell: \\c cancels the statement currently being entered" {
+    skiponwindows "Need to install expect and make this script work on windows."
+    if [ "$SQL_ENGINE" = "remote-engine" ]; then
+      skip "Current test setup results in remote calls having a clean branch, where this expect script expects dirty."
+    fi
+    run $BATS_TEST_DIRNAME/sql-shell-clear-statement.expect
+    echo "$output"
+
+    [ "$status" -eq 0 ]
+    # \c must not have been folded into the next statement (a bug would surface as a syntax
+    # error near the stray backslash), and the next statement must have actually executed.
+    [[ ! "$output" =~ "syntax error" ]] || false
+    [[ "$output" =~ "1 row in set" ]] || false
+}
+
 # Regression coverage for https://github.com/dolthub/dolt/issues/11137
 # bats test_tags=no_lambda
 @test "sql-shell: status slash command works without --branch flag" {