Adjust behavior of single-user -j mode for better initdb error reporting.

Previously, -j caused the entire input file to be read in and executed as
a single command string.  That's undesirable, not least because any error
causes the entire file to be regurgitated as the "failing query".  Some
experimentation suggests a better rule: end the command string when we see
a semicolon immediately followed by two newlines, ie, an empty line after
a query.  This serves nicely to break up the existing examples such as
information_schema.sql and system_views.sql.  A limitation is that it's
no longer possible to write such a sequence within a string literal or
multiline comment in a file meant to be read with -j; but there are no
instances of such a problem within the data currently used by initdb.
(If someone does make such a mistake in future, it'll be obvious because
they'll get an unterminated-literal or unterminated-comment syntax error.)
Other than that, there shouldn't be any negative consequences; you're not
forced to end statements that way, it's just a better idea in most cases.

In passing, remove src/include/tcop/tcopdebug.h, which is dead code
because it's not included anywhere, and hasn't been for more than
ten years.  One of the debug-support symbols it purported to describe
has been unreferenced for at least the same amount of time, and the
other is removed by this commit on the grounds that it was useless:
forcing -j mode all the time would have broken initdb.  The lack of
complaints about that, or about the missing inclusion, shows that
no one has tried to use TCOP_DONTUSENEWLINE in many years.

1 files changed, 35 insertions, 46 deletions

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 1dc2eb0fcca..4ae25487ef4 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -157,18 +157,8 @@ static CachedPlanSource *unnamed_stmt_psrc = NULL;
 
 /* assorted command-line switches */
 static const char *userDoption = NULL;	/* -D switch */
-
 static bool EchoQuery = false;	/* -E switch */
-
-/*
- * people who want to use EOF should #define DONTUSENEWLINE in
- * tcop/tcopdebug.h
- */
-#ifndef TCOP_DONTUSENEWLINE
-static int	UseNewLine = 1;		/* Use newlines query delimiters (the default) */
-#else
-static int	UseNewLine = 0;		/* Use EOF as query delimiters */
-#endif   /* TCOP_DONTUSENEWLINE */
+static bool UseSemiNewlineNewline = false;		/* -j switch */
 
 /* whether or not, and why, we were canceled by conflict with recovery */
 static bool RecoveryConflictPending = false;
@@ -219,8 +209,6 @@ static int
 InteractiveBackend(StringInfo inBuf)
 {
 	int			c;				/* character read from getc() */
-	bool		end = false;	/* end-of-input flag */
-	bool		backslashSeen = false;	/* have we seen a \ ? */
 
 	/*
 	 * display a prompt and obtain input from the user
@@ -230,55 +218,56 @@ InteractiveBackend(StringInfo inBuf)
 
 	resetStringInfo(inBuf);
 
-	if (UseNewLine)
+	/*
+	 * Read characters until EOF or the appropriate delimiter is seen.
+	 */
+	while ((c = interactive_getc()) != EOF)
 	{
-		/*
-		 * if we are using \n as a delimiter, then read characters until the
-		 * \n.
-		 */
-		while ((c = interactive_getc()) != EOF)
+		if (c == '\n')
 		{
-			if (c == '\n')
+			if (UseSemiNewlineNewline)
 			{
-				if (backslashSeen)
+				/*
+				 * In -j mode, semicolon followed by two newlines ends the
+				 * command; otherwise treat newline as regular character.
+				 */
+				if (inBuf->len > 1 &&
+					inBuf->data[inBuf->len - 1] == '\n' &&
+					inBuf->data[inBuf->len - 2] == ';')
+				{
+					/* might as well drop the second newline */
+					break;
+				}
+			}
+			else
+			{
+				/*
+				 * In plain mode, newline ends the command unless preceded by
+				 * backslash.
+				 */
+				if (inBuf->len > 0 &&
+					inBuf->data[inBuf->len - 1] == '\\')
 				{
 					/* discard backslash from inBuf */
 					inBuf->data[--inBuf->len] = '\0';
-					backslashSeen = false;
+					/* discard newline too */
 					continue;
 				}
 				else
 				{
-					/* keep the newline character */
+					/* keep the newline character, but end the command */
 					appendStringInfoChar(inBuf, '\n');
 					break;
 				}
 			}
-			else if (c == '\\')
-				backslashSeen = true;
-			else
-				backslashSeen = false;
-
-			appendStringInfoChar(inBuf, (char) c);
 		}
 
-		if (c == EOF)
-			end = true;
-	}
-	else
-	{
-		/*
-		 * otherwise read characters until EOF.
-		 */
-		while ((c = interactive_getc()) != EOF)
-			appendStringInfoChar(inBuf, (char) c);
-
-		/* No input before EOF signal means time to quit. */
-		if (inBuf->len == 0)
-			end = true;
+		/* Not newline, or newline treated as regular character */
+		appendStringInfoChar(inBuf, (char) c);
 	}
 
-	if (end)
+	/* No input before EOF signal means time to quit. */
+	if (c == EOF && inBuf->len == 0)
 		return EOF;
 
 	/*
@@ -3391,7 +3380,7 @@ process_postgres_switches(int argc, char *argv[], GucContext ctx,
 
 			case 'j':
 				if (secure)
-					UseNewLine = 0;
+					UseSemiNewlineNewline = true;
 				break;
 
 			case 'k':
@@ -3901,7 +3890,7 @@ PostgresMain(int argc, char *argv[],
 		if (pq_is_reading_msg())
 			ereport(FATAL,
 					(errcode(ERRCODE_PROTOCOL_VIOLATION),
-			errmsg("terminating connection because protocol synchronization was lost")));
+					 errmsg("terminating connection because protocol synchronization was lost")));
 
 		/* Now we can allow interrupts again */
 		RESUME_INTERRUPTS();