Added hook to set common typmod for case expression (#452)

Issue:

\Return type of overall CASE expression when branch expression is of String Datatype, is evaluated to give typmod error message if the common type is CHAR/NCHAR.

eg. If the Common type evaluated is CHAR/NCHAR

SELECT CASE 1
    WHEN 1 THEN NULL
    WHEN 2 THEN CAST('char' AS CHAR(10))
END
GO

Output: Msg 33557097, Level 16, State 1, Server BABELFISH, Line 1
The string size for the given CHAR/NCHAR data is not defined. Please use an explicit CAST or CONVERT to CHAR(n)/NCHAR(n).

Expected output:
CHAR
NULL

Changes made to fix the issues:

Implementing a hook that calculates the resultant typmod for the CASE expression, and also set typmod for all the CASE branches when .

Task: BABEL-5103, BABEL-4332
Signed-off-by: Yashneet Vinayak <[email protected]>

src/backend/parser/parse_expr.c

@@ -101,6 +101,7 @@ static List *ExpandChecksumStar(ParseState *pstate, FuncCall *fn, int location);
 
 lookup_param_hook_type lookup_param_hook = NULL;
 handle_constant_literals_hook_type handle_constant_literals_hook = NULL;
+set_common_typmod_case_expr_hook_type set_common_typmod_case_expr_hook = NULL;
 /*
  * transformExpr -
  *	  Analyze and transform expressions. Type checking and type casting is
@@ -1834,6 +1835,10 @@ transformCaseExpr(ParseState *pstate, CaseExpr *c)
 
 	newc->location = c->location;
 
+	/* Following hook will be used to set the typmod of all the CASE Branches. */
+	if (sql_dialect == SQL_DIALECT_TSQL && set_common_typmod_case_expr_hook)
+		(*set_common_typmod_case_expr_hook)(pstate, resultexprs, newc);
+
 	return (Node *) newc;
 }
 

src/include/parser/parse_coerce.h

@@ -137,4 +137,7 @@ typedef int32 (*select_common_typmod_hook_type) (ParseState *pstate, List *exprs
 typedef Node *(*handle_constant_literals_hook_type) (ParseState *pstate, Node *e);
 extern PGDLLEXPORT handle_constant_literals_hook_type handle_constant_literals_hook;
 
+typedef void (*set_common_typmod_case_expr_hook_type) (ParseState *pstate, List *exprs, CaseExpr *newc);
+extern PGDLLIMPORT set_common_typmod_case_expr_hook_type set_common_typmod_case_expr_hook;
+
 #endif							/* PARSE_COERCE_H */