Make plpgsql's unreserved keywords more unreserved.

There were assorted places where unreserved keywords were not treated the
same as T_WORD (that is, a random unrecognized identifier).  Fix them.
It might not always be possible to allow this, but it is in all these
places, so I don't see any downside.

Per gripe from Jim Wilson.  Arguably this is a bug fix, but given the lack
of other complaints and the ease of working around it (just quote the
word), I won't risk back-patching.

src/pl/plpgsql/src/gram.y

@@ -642,6 +642,21 @@ decl_aliasitem	: T_WORD
 									 parser_errposition(@1)));
 						$$ = nsi;
 					}
+				| unreserved_keyword
+					{
+						PLpgSQL_nsitem *nsi;
+
+						nsi = plpgsql_ns_lookup(plpgsql_ns_top(), false,
+												$1, NULL, NULL,
+												NULL);
+						if (nsi == NULL)
+							ereport(ERROR,
+									(errcode(ERRCODE_UNDEFINED_OBJECT),
+									 errmsg("variable \"%s\" does not exist",
+											$1),
+									 parser_errposition(@1)));
+						$$ = nsi;
+					}
 				| T_CWORD
 					{
 						PLpgSQL_nsitem *nsi;
@@ -722,6 +737,11 @@ decl_collate	:
 						$$ = get_collation_oid(list_make1(makeString($2.ident)),
 											   false);
 					}
+				| K_COLLATE unreserved_keyword
+					{
+						$$ = get_collation_oid(list_make1(makeString(pstrdup($2))),
+											   false);
+					}
 				| K_COLLATE T_CWORD
 					{
 						$$ = get_collation_oid($2.idents, false);
@@ -1720,9 +1740,12 @@ stmt_raise		: K_RAISE
 								}
 								else
 								{
-									if (tok != T_WORD)
+									if (tok == T_WORD)
+										new->condname = yylval.word.ident;
+									else if (plpgsql_token_is_unreserved_keyword(tok))
+										new->condname = pstrdup(yylval.keyword);
+									else
 										yyerror("syntax error");
-									new->condname = yylval.word.ident;
 									plpgsql_recognize_err_condition(new->condname,
 																	false);
 								}
@@ -2185,12 +2208,16 @@ opt_exitcond	: ';'
 				;
 
 /*
- * need both options because scanner will have tried to resolve as variable
+ * need to allow DATUM because scanner will have tried to resolve as variable
  */
 any_identifier	: T_WORD
 					{
 						$$ = $1.ident;
 					}
+				| unreserved_keyword
+					{
+						$$ = pstrdup($1);
+					}
 				| T_DATUM
 					{
 						if ($1.ident == NULL) /* composite name not OK */
@@ -2513,6 +2540,30 @@ read_datatype(int tok)
 			}
 		}
 	}
+	else if (plpgsql_token_is_unreserved_keyword(tok))
+	{
+		char   *dtname = pstrdup(yylval.keyword);
+
+		tok = yylex();
+		if (tok == '%')
+		{
+			tok = yylex();
+			if (tok_is_keyword(tok, &yylval,
+							   K_TYPE, "type"))
+			{
+				result = plpgsql_parse_wordtype(dtname);
+				if (result)
+					return result;
+			}
+			else if (tok_is_keyword(tok, &yylval,
+									K_ROWTYPE, "rowtype"))
+			{
+				result = plpgsql_parse_wordrowtype(dtname);
+				if (result)
+					return result;
+			}
+		}
+	}
 	else if (tok == T_CWORD)
 	{
 		List   *dtnames = yylval.cword.idents;

src/pl/plpgsql/src/pl_scanner.c

@@ -410,6 +410,25 @@ plpgsql_push_back_token(int token)
 	push_back_token(token, &auxdata);
 }
 
+/*
+ * Tell whether a token is an unreserved keyword.
+ *
+ * (If it is, its lowercased form was returned as the token value, so we
+ * do not need to offer that data here.)
+ */
+bool
+plpgsql_token_is_unreserved_keyword(int token)
+{
+	int			i;
+
+	for (i = 0; i < num_unreserved_keywords; i++)
+	{
+		if (unreserved_keywords[i].value == token)
+			return true;
+	}
+	return false;
+}
+
 /*
  * Append the function text starting at startlocation and extending to
  * (not including) endlocation onto the existing contents of "buf".

src/pl/plpgsql/src/plpgsql.h

@@ -973,6 +973,7 @@ extern void plpgsql_dumptree(PLpgSQL_function *func);
 extern int	plpgsql_base_yylex(void);
 extern int	plpgsql_yylex(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,
 						   int startlocation, int endlocation);
 extern void plpgsql_peek2(int *tok1_p, int *tok2_p, int *tok1_loc,