WIP patch for allowing COLLATE in plpgsql variable declarations

The attached code patch (seems to work, but no regression tests or doc
fixes yet) allows plpgsql variable declarations like

    declare
      x text collate "en_US";

Such a collation spec overrides the default variable collation that is
otherwise inherited from the function's input collation.  I believe
this is essentially what we agreed to do a couple weeks ago.
Comments, objections?

            regards, tom lane

diff --git a/src/pl/plpgsql/src/gram.y b/src/pl/plpgsql/src/gram.y
index fbd441a1bc986835d9dc8729ff61ab61ee4d06d4..4e2b7058f0c471182b8276a101e33fa96ed01bdb 100644
*** a/src/pl/plpgsql/src/gram.y
--- b/src/pl/plpgsql/src/gram.y
***************
*** 21,26 ****
--- 21,27 ----
  #include "parser/parse_type.h"
  #include "parser/scanner.h"
  #include "parser/scansup.h"
+ #include "utils/builtins.h"


  /* Location tracking support --- simpler than bison's default */
*************** static    List            *read_raise_options(void);
*** 122,127 ****
--- 123,129 ----
          PLcword                    cword;
          PLwdatum                wdatum;
          bool                    boolean;
+         Oid                        oid;
          struct
          {
              char *name;
*************** static    List            *read_raise_options(void);
*** 167,172 ****
--- 169,175 ----
  %type <boolean>    decl_const decl_notnull exit_type
  %type <expr>    decl_defval decl_cursor_query
  %type <dtype>    decl_datatype
+ %type <oid>        decl_collate
  %type <datum>    decl_cursor_args
  %type <list>    decl_cursor_arglist
  %type <nsitem>    decl_aliasitem
*************** static    List            *read_raise_options(void);
*** 245,250 ****
--- 248,254 ----
  %token <keyword>    K_BY
  %token <keyword>    K_CASE
  %token <keyword>    K_CLOSE
+ %token <keyword>    K_COLLATE
  %token <keyword>    K_CONSTANT
  %token <keyword>    K_CONTINUE
  %token <keyword>    K_CURSOR
*************** decl_stmt        : decl_statement
*** 428,437 ****
                      }
                  ;

! decl_statement    : decl_varname decl_const decl_datatype decl_notnull decl_defval
                      {
                          PLpgSQL_variable    *var;

                          var = plpgsql_build_variable($1.name, $1.lineno,
                                                       $3, true);
                          if ($2)
--- 432,458 ----
                      }
                  ;

! decl_statement    : decl_varname decl_const decl_datatype decl_collate decl_notnull decl_defval
                      {
                          PLpgSQL_variable    *var;

+                         /*
+                          * If a collation is supplied, insert it into the
+                          * datatype.  We assume decl_datatype always returns
+                          * a freshly built struct not shared with other
+                          * variables.
+                          */
+                         if (OidIsValid($4))
+                         {
+                             if (!OidIsValid($3->collation))
+                                 ereport(ERROR,
+                                         (errcode(ERRCODE_DATATYPE_MISMATCH),
+                                          errmsg("collations are not supported by type %s",
+                                                 format_type_be($3->typoid)),
+                                          parser_errposition(@4)));
+                             $3->collation = $4;
+                         }
+
                          var = plpgsql_build_variable($1.name, $1.lineno,
                                                       $3, true);
                          if ($2)
*************** decl_statement    : decl_varname decl_const
*** 444,453 ****
                                           errmsg("row or record variable cannot be CONSTANT"),
                                           parser_errposition(@2)));
                          }
!                         if ($4)
                          {
                              if (var->dtype == PLPGSQL_DTYPE_VAR)
!                                 ((PLpgSQL_var *) var)->notnull = $4;
                              else
                                  ereport(ERROR,
                                          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
--- 465,474 ----
                                           errmsg("row or record variable cannot be CONSTANT"),
                                           parser_errposition(@2)));
                          }
!                         if ($5)
                          {
                              if (var->dtype == PLPGSQL_DTYPE_VAR)
!                                 ((PLpgSQL_var *) var)->notnull = $5;
                              else
                                  ereport(ERROR,
                                          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
*************** decl_statement    : decl_varname decl_const
*** 455,464 ****
                                           parser_errposition(@4)));

                          }
!                         if ($5 != NULL)
                          {
                              if (var->dtype == PLPGSQL_DTYPE_VAR)
!                                 ((PLpgSQL_var *) var)->default_val = $5;
                              else
                                  ereport(ERROR,
                                          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
--- 476,485 ----
                                           parser_errposition(@4)));

                          }
!                         if ($6 != NULL)
                          {
                              if (var->dtype == PLPGSQL_DTYPE_VAR)
!                                 ((PLpgSQL_var *) var)->default_val = $6;
                              else
                                  ereport(ERROR,
                                          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
*************** decl_datatype    :
*** 685,690 ****
--- 706,724 ----
                      }
                  ;

+ decl_collate    :
+                     { $$ = InvalidOid; }
+                 | K_COLLATE T_WORD
+                     {
+                         $$ = get_collation_oid(list_make1(makeString($2.ident)),
+                                                false);
+                     }
+                 | K_COLLATE T_CWORD
+                     {
+                         $$ = get_collation_oid($2.idents, false);
+                     }
+                 ;
+
  decl_notnull    :
                      { $$ = false; }
                  | K_NOT K_NULL
*************** read_datatype(int tok)
*** 2432,2438 ****
                  yyerror("incomplete data type declaration");
          }
          /* Possible followers for datatype in a declaration */
!         if (tok == K_NOT || tok == '=' || tok == COLON_EQUALS || tok == K_DEFAULT)
              break;
          /* Possible followers for datatype in a cursor_arg list */
          if ((tok == ',' || tok == ')') && parenlevel == 0)
--- 2466,2473 ----
                  yyerror("incomplete data type declaration");
          }
          /* Possible followers for datatype in a declaration */
!         if (tok == K_COLLATE || tok == K_NOT ||
!             tok == '=' || tok == COLON_EQUALS || tok == K_DEFAULT)
              break;
          /* Possible followers for datatype in a cursor_arg list */
          if ((tok == ',' || tok == ')') && parenlevel == 0)
diff --git a/src/pl/plpgsql/src/pl_scanner.c b/src/pl/plpgsql/src/pl_scanner.c
index e8a2628f2f1dfbdd6ba466d7216c3a2ee0906d19..e1c0b625954a6c6cee45932e849df681e8d1508b 100644
*** a/src/pl/plpgsql/src/pl_scanner.c
--- b/src/pl/plpgsql/src/pl_scanner.c
*************** static const ScanKeyword reserved_keywor
*** 64,69 ****
--- 64,70 ----
      PG_KEYWORD("by", K_BY, RESERVED_KEYWORD)
      PG_KEYWORD("case", K_CASE, RESERVED_KEYWORD)
      PG_KEYWORD("close", K_CLOSE, RESERVED_KEYWORD)
+     PG_KEYWORD("collate", K_COLLATE, RESERVED_KEYWORD)
      PG_KEYWORD("continue", K_CONTINUE, RESERVED_KEYWORD)
      PG_KEYWORD("declare", K_DECLARE, RESERVED_KEYWORD)
      PG_KEYWORD("default", K_DEFAULT, RESERVED_KEYWORD)