Fix plpgsql's handling of -- comments following expressions.

Up to now, read_sql_construct() has collected all the source text from
the statement or expression's initial token up to the character just
before the "until" token.  It normally tries to strip trailing
whitespace from that, largely for neatness.  If there was a "-- text"
comment after the expression, this resulted in removing the newline
that terminates the comment, which creates a hazard if we try to paste
the collected text into a larger SQL construct without inserting a
newline after it.  In particular this caused our handling of CASE
constructs to fail if there's a comment after a WHEN expression.

Commit 4adead1d2 noticed a similar problem with cursor arguments,
and worked around it through the rather crude hack of suppressing
the whitespace-trimming behavior for those.  Rather than do that
and leave the hazard open for future hackers to trip over, let's
fix it properly.  pl_scanner.c already has enough infrastructure
to report the end location of the expression's last token, so
we can copy up to that location and never collect any trailing
whitespace or comment to begin with.

Erik Wienhold and Tom Lane, per report from Michal Bartak.
Back-patch to all supported branches.

Discussion: https://postgr.es/m/CAAVzF_FjRoi8fOVuLCZhQJx6HATQ7MKm=aFOHWZODFnLmjX-xA@mail.gmail.com

src/pl/plpgsql/src/expected/plpgsql_control.out

@@ -681,3 +681,20 @@ select case_test(13);
  other
 (1 row)
 
+-- test line comment between WHEN and THEN
+create or replace function case_comment(int) returns text as $$
+begin
+  case $1
+    when 1 -- comment before THEN
+      then return 'one';
+    else
+      return 'other';
+  end case;
+end;
+$$ language plpgsql immutable;
+select case_comment(1);
+ case_comment 
+--------------
+ one
+(1 row)
+

src/pl/plpgsql/src/pl_gram.y

@@ -69,7 +69,6 @@ static	PLpgSQL_expr	*read_sql_construct(int until,
 											RawParseMode parsemode,
 											bool isexpression,
 											bool valid_sql,
-											bool trim,
 											int *startloc,
 											int *endtoken);
 static	PLpgSQL_expr	*read_sql_expression(int until,
@@ -921,7 +920,7 @@ stmt_perform	: K_PERFORM
 						 */
 						new->expr = read_sql_construct(';', 0, 0, ";",
 													   RAW_PARSE_DEFAULT,
-													   false, false, true,
+													   false, false,
 													   &startloc, NULL);
 						/* overwrite "perform" ... */
 						memcpy(new->expr->query, " SELECT", 7);
@@ -1007,7 +1006,7 @@ stmt_assign		: T_DATUM
 						plpgsql_push_back_token(T_DATUM);
 						new->expr = read_sql_construct(';', 0, 0, ";",
 													   pmode,
-													   false, true, true,
+													   false, true,
 													   NULL, NULL);
 
 						$$ = (PLpgSQL_stmt *)new;
@@ -1496,7 +1495,6 @@ for_control		: for_variable K_IN
 													   RAW_PARSE_DEFAULT,
 													   true,
 													   false,
-													   true,
 													   &expr1loc,
 													   &tok);
 
@@ -1901,7 +1899,7 @@ stmt_raise		: K_RAISE
 									expr = read_sql_construct(',', ';', K_USING,
 															  ", or ; or USING",
 															  RAW_PARSE_PLPGSQL_EXPR,
-															  true, true, true,
+															  true, true,
 															  NULL, &tok);
 									new->params = lappend(new->params, expr);
 								}
@@ -2034,7 +2032,7 @@ stmt_dynexecute : K_EXECUTE
 						expr = read_sql_construct(K_INTO, K_USING, ';',
 												  "INTO or USING or ;",
 												  RAW_PARSE_PLPGSQL_EXPR,
-												  true, true, true,
+												  true, true,
 												  NULL, &endtoken);
 
 						new = palloc(sizeof(PLpgSQL_stmt_dynexecute));
@@ -2073,7 +2071,7 @@ stmt_dynexecute : K_EXECUTE
 									expr = read_sql_construct(',', ';', K_INTO,
 															  ", or ; or INTO",
 															  RAW_PARSE_PLPGSQL_EXPR,
-															  true, true, true,
+															  true, true,
 															  NULL, &endtoken);
 									new->params = lappend(new->params, expr);
 								} while (endtoken == ',');
@@ -2656,7 +2654,7 @@ read_sql_expression(int until, const char *expected)
 {
 	return read_sql_construct(until, 0, 0, expected,
 							  RAW_PARSE_PLPGSQL_EXPR,
-							  true, true, true, NULL, NULL);
+							  true, true, NULL, NULL);
 }
 
 /* Convenience routine to read an expression with two possible terminators */
@@ -2666,7 +2664,7 @@ read_sql_expression2(int until, int until2, const char *expected,
 {
 	return read_sql_construct(until, until2, 0, expected,
 							  RAW_PARSE_PLPGSQL_EXPR,
-							  true, true, true, NULL, endtoken);
+							  true, true, NULL, endtoken);
 }
 
 /* Convenience routine to read a SQL statement that must end with ';' */
@@ -2675,7 +2673,7 @@ read_sql_stmt(void)
 {
 	return read_sql_construct(';', 0, 0, ";",
 							  RAW_PARSE_DEFAULT,
-							  false, true, true, NULL, NULL);
+							  false, true, NULL, NULL);
 }
 
 /*
@@ -2688,7 +2686,6 @@ read_sql_stmt(void)
  * parsemode:	raw_parser() mode to use
  * isexpression: whether to say we're reading an "expression" or a "statement"
  * valid_sql:   whether to check the syntax of the expr
- * trim:		trim trailing whitespace
  * startloc:	if not NULL, location of first token is stored at *startloc
  * endtoken:	if not NULL, ending token is stored at *endtoken
  *				(this is only interesting if until2 or until3 isn't zero)
@@ -2701,7 +2698,6 @@ read_sql_construct(int until,
 				   RawParseMode parsemode,
 				   bool isexpression,
 				   bool valid_sql,
-				   bool trim,
 				   int *startloc,
 				   int *endtoken)
 {
@@ -2709,6 +2705,7 @@ read_sql_construct(int until,
 	StringInfoData		ds;
 	IdentifierLookup	save_IdentifierLookup;
 	int					startlocation = -1;
+	int					endlocation = -1;
 	int					parenlevel = 0;
 	PLpgSQL_expr		*expr;
 
@@ -2759,6 +2756,8 @@ read_sql_construct(int until,
 								expected),
 						 parser_errposition(yylloc)));
 		}
+		/* Remember end+1 location of last accepted token */
+		endlocation = yylloc + plpgsql_token_length();
 	}
 
 	plpgsql_IdentifierLookup = save_IdentifierLookup;
@@ -2769,7 +2768,7 @@ read_sql_construct(int until,
 		*endtoken = tok;
 
 	/* give helpful complaint about empty input */
-	if (startlocation >= yylloc)
+	if (startlocation >= endlocation)
 	{
 		if (isexpression)
 			yyerror("missing expression");
@@ -2777,14 +2776,14 @@ read_sql_construct(int until,
 			yyerror("missing SQL statement");
 	}
 
-	plpgsql_append_source_text(&ds, startlocation, yylloc);
-
-	/* trim any trailing whitespace, for neatness */
-	if (trim)
-	{
-		while (ds.len > 0 && scanner_isspace(ds.data[ds.len - 1]))
-			ds.data[--ds.len] = '\0';
-	}
+	/*
+	 * We save only the text from startlocation to endlocation-1.  This
+	 * suppresses the "until" token as well as any whitespace or comments
+	 * following the last accepted token.  (We used to strip such trailing
+	 * whitespace by hand, but that causes problems if there's a "-- comment"
+	 * in front of said whitespace.)
+	 */
+	plpgsql_append_source_text(&ds, startlocation, endlocation);
 
 	expr = palloc0(sizeof(PLpgSQL_expr));
 	expr->query			= pstrdup(ds.data);
@@ -3923,16 +3922,12 @@ read_cursor_args(PLpgSQL_var *cursor, int until)
 		 * Read the value expression. To provide the user with meaningful
 		 * parse error positions, we check the syntax immediately, instead of
 		 * checking the final expression that may have the arguments
-		 * reordered. Trailing whitespace must not be trimmed, because
-		 * otherwise input of the form (param -- comment\n, param) would be
-		 * translated into a form where the second parameter is commented
-		 * out.
+		 * reordered.
 		 */
 		item = read_sql_construct(',', ')', 0,
 								  ",\" or \")",
 								  RAW_PARSE_PLPGSQL_EXPR,
 								  true, true,
-								  false, /* do not trim */
 								  NULL, &endtoken);
 
 		argv[argpos] = item->query;

src/pl/plpgsql/src/pl_scanner.c

@@ -184,6 +184,8 @@ plpgsql_yylex(void)
 							tok1 = T_DATUM;
 						else
 							tok1 = T_CWORD;
+						/* Adjust token length to include A.B.C */
+						aux1.leng = aux5.lloc - aux1.lloc + aux5.leng;
 					}
 					else
 					{
@@ -197,6 +199,8 @@ plpgsql_yylex(void)
 							tok1 = T_DATUM;
 						else
 							tok1 = T_CWORD;
+						/* Adjust token length to include A.B */
+						aux1.leng = aux3.lloc - aux1.lloc + aux3.leng;
 					}
 				}
 				else
@@ -210,6 +214,8 @@ plpgsql_yylex(void)
 						tok1 = T_DATUM;
 					else
 						tok1 = T_CWORD;
+					/* Adjust token length to include A.B */
+					aux1.leng = aux3.lloc - aux1.lloc + aux3.leng;
 				}
 			}
 			else
@@ -298,6 +304,17 @@ plpgsql_yylex(void)
 	return tok1;
 }
 
+/*
+ * Return the length of the token last returned by plpgsql_yylex().
+ *
+ * In the case of compound tokens, the length includes all the parts.
+ */
+int
+plpgsql_token_length(void)
+{
+	return plpgsql_yyleng;
+}
+
 /*
  * Internal yylex function.  This wraps the core lexer and adds one feature:
  * a token pushback stack.  We also make a couple of trivial single-token

src/pl/plpgsql/src/plpgsql.h

@@ -1302,6 +1302,7 @@ extern void plpgsql_dumptree(PLpgSQL_function *func);
  */
 extern int	plpgsql_base_yylex(void);
 extern int	plpgsql_yylex(void);
+extern int	plpgsql_token_length(void);
 extern void plpgsql_push_back_token(int token);
 extern bool plpgsql_token_is_unreserved_keyword(int token);
 extern void plpgsql_append_source_text(StringInfo buf,

src/pl/plpgsql/src/sql/plpgsql_control.sql

@@ -486,3 +486,17 @@ select case_test(1);
 select case_test(2);
 select case_test(12);
 select case_test(13);
+
+-- test line comment between WHEN and THEN
+create or replace function case_comment(int) returns text as $$
+begin
+  case $1
+    when 1 -- comment before THEN
+      then return 'one';
+    else
+      return 'other';
+  end case;
+end;
+$$ language plpgsql immutable;
+
+select case_comment(1);

src/test/regress/expected/plpgsql.out

@@ -2363,11 +2363,9 @@ select namedparmcursor_test7();
 ERROR:  division by zero
 CONTEXT:  SQL expression "42/0 AS p1, 77 AS p2"
 PL/pgSQL function namedparmcursor_test7() line 6 at OPEN
--- check that line comments work correctly within the argument list (there
--- is some special handling of this case in the code: the newline after the
--- comment must be preserved when the argument-evaluating query is
--- constructed, otherwise the comment effectively comments out the next
--- argument, too)
+-- check that line comments work correctly within the argument list
+-- (this used to require a special hack in the code; it no longer does,
+-- but let's keep the test anyway)
 create function namedparmcursor_test8() returns int4 as $$
 declare
   c1 cursor (p1 int, p2 int) for

src/test/regress/sql/plpgsql.sql

@@ -2023,11 +2023,9 @@ begin
 end $$ language plpgsql;
 select namedparmcursor_test7();
 
--- check that line comments work correctly within the argument list (there
--- is some special handling of this case in the code: the newline after the
--- comment must be preserved when the argument-evaluating query is
--- constructed, otherwise the comment effectively comments out the next
--- argument, too)
+-- check that line comments work correctly within the argument list
+-- (this used to require a special hack in the code; it no longer does,
+-- but let's keep the test anyway)
 create function namedparmcursor_test8() returns int4 as $$
 declare
   c1 cursor (p1 int, p2 int) for