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Fix shift/reduce conflict in grammar #1719

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Apr 4, 2024
Merged

Fix shift/reduce conflict in grammar #1719

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9 changes: 9 additions & 0 deletions regress/expected/list_comprehension.out
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Original file line number Diff line number Diff line change
Expand Up @@ -571,6 +571,15 @@ SELECT * FROM cypher('list_comprehension', $$ RETURN [i IN range(0, 10, 2) WHERE
ERROR: could not find rte for i
LINE 1: ...$$ RETURN [i IN range(0, 10, 2) WHERE i>5 | i^2], i $$) AS (...
^
-- Invalid list comprehension
SELECT * FROM cypher('list_comprehension', $$ RETURN [1 IN range(0, 10, 2) WHERE 2>5] $$) AS (result agtype);
ERROR: Syntax error at or near IN
LINE 1: SELECT * FROM cypher('list_comprehension', $$ RETURN [1 IN r...
^
SELECT * FROM cypher('list_comprehension', $$ RETURN [1 IN range(0, 10, 2) | 1] $$) AS (result agtype);
ERROR: Syntax error at or near IN
LINE 1: SELECT * FROM cypher('list_comprehension', $$ RETURN [1 IN r...
^
SELECT * FROM drop_graph('list_comprehension', true);
NOTICE: drop cascades to 4 other objects
DETAIL: drop cascades to table list_comprehension._ag_label_vertex
Expand Down
4 changes: 4 additions & 0 deletions regress/sql/list_comprehension.sql
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Expand Up @@ -145,4 +145,8 @@ SELECT * FROM cypher('list_comprehension', $$ WITH [u IN [1,2,3]] AS u, [u IN [1
SELECT * FROM cypher('list_comprehension', $$ RETURN [i IN range(0, 10, 2)],i $$) AS (result agtype, i agtype);
SELECT * FROM cypher('list_comprehension', $$ RETURN [i IN range(0, 10, 2) WHERE i>5 | i^2], i $$) AS (result agtype, i agtype);

-- Invalid list comprehension
SELECT * FROM cypher('list_comprehension', $$ RETURN [1 IN range(0, 10, 2) WHERE 2>5] $$) AS (result agtype);
SELECT * FROM cypher('list_comprehension', $$ RETURN [1 IN range(0, 10, 2) | 1] $$) AS (result agtype);

SELECT * FROM drop_graph('list_comprehension', true);
122 changes: 90 additions & 32 deletions src/backend/parser/cypher_gram.y
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Expand Up @@ -136,9 +136,6 @@
/* common */
%type <node> where_opt

/* list comprehension optional mapping expression */
%type <node> mapping_expr_opt

/* pattern */
%type <list> pattern simple_path_opt_parens simple_path
%type <node> path anonymous_path
Expand Down Expand Up @@ -250,7 +247,12 @@ static Node *build_comparison_expression(Node *left_grammar_node,
char *opr_name, int location);

// list_comprehension
static Node *build_list_comprehension_node(char *var_name, Node *expr,
static Node *verify_rule_as_list_comprehension(Node *expr, Node *expr2,
Node *where, Node *mapping_expr,
int var_loc, int expr_loc,
int where_loc, int mapping_loc);

static Node *build_list_comprehension_node(ColumnRef *var_name, Node *expr,
Node *where, Node *mapping_expr,
int var_loc, int expr_loc,
int where_loc,int mapping_loc);
Expand Down Expand Up @@ -1911,20 +1913,51 @@ list:

$$ = (Node *)n;
}
| '[' list_comprehension ']'
{
$$ = $2;
}
| list_comprehension
;

mapping_expr_opt:
/* empty */
/*
* This grammar rule is generic to some extent. It can
* evaluate to either IN operator or list comprehension.
* This avoids shift/reduce errors between the two rules.
*/
list_comprehension:
'[' expr IN expr ']'
{
$$ = NULL;
Node *n = $2;
Node *result = NULL;

/*
* If the first expr is a ColumnRef(variable), then the rule
* should evaluate as a list comprehension. Otherwise, it should
* evaluate as an IN operator.
*/
if (nodeTag(n) == T_ColumnRef)
{
ColumnRef *cref = (ColumnRef *)n;
result = build_list_comprehension_node(cref, $4, NULL, NULL,
@2, @4, 0, 0);
}
else
{
result = (Node *)makeSimpleA_Expr(AEXPR_IN, "=", n, $4, @3);
}
$$ = result;
}
| '|' expr
| '[' expr IN expr WHERE expr ']'
{
$$ = $2;
$$ = verify_rule_as_list_comprehension($2, $4, $6, NULL,
@2, @4, @6, 0);
}
| '[' expr IN expr '|' expr ']'
{
$$ = verify_rule_as_list_comprehension($2, $4, NULL, $6,
@2, @4, 0, @6);
}
| '[' expr IN expr WHERE expr '|' expr ']'
{
$$ = verify_rule_as_list_comprehension($2, $4, $6, $8,
@2, @4, @6, @8);
}
;

Expand Down Expand Up @@ -1989,14 +2022,6 @@ expr_case_default:
}
;

list_comprehension:
var_name IN expr where_opt mapping_expr_opt
{
$$ = build_list_comprehension_node($1, $3, $4, $5,
@1, @3, @4, @5);
}
;

expr_var:
var_name
{
Expand Down Expand Up @@ -2962,15 +2987,57 @@ static cypher_relationship *build_VLE_relation(List *left_arg,
return cr;
}

// Helper function to verify that the rule is a list comprehension
static Node *verify_rule_as_list_comprehension(Node *expr, Node *expr2,
Node *where, Node *mapping_expr,
int var_loc, int expr_loc,
int where_loc, int mapping_loc)
{
Node *result = NULL;

/*
* If the first expression is a ColumnRef, then we can build a
* list_comprehension node.
* Else its an invalid use of IN operator.
*/
if (nodeTag(expr) == T_ColumnRef)
{
ColumnRef *cref = (ColumnRef *)expr;
result = build_list_comprehension_node(cref, expr2, where,
mapping_expr, var_loc,
expr_loc, where_loc,
mapping_loc);
}
else
{
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("Syntax error at or near IN")));
}
return result;
}

/* helper function to build a list_comprehension grammar node */
static Node *build_list_comprehension_node(char *var_name, Node *expr,
static Node *build_list_comprehension_node(ColumnRef *cref, Node *expr,
Node *where, Node *mapping_expr,
int var_loc, int expr_loc,
int where_loc, int mapping_loc)
{
ResTarget *res = NULL;
cypher_unwind *unwind = NULL;
ColumnRef *cref = NULL;
char *var_name = NULL;
String *val;

// Extract name from cref
val = linitial(cref->fields);

if (!IsA(val, String))
{
ereport(ERROR,
(errmsg_internal("unexpected Node for cypher_clause")));
}

var_name = val->sval;

/*
* Build the ResTarget node for the UNWIND variable var_name attached to
Expand All @@ -2984,15 +3051,6 @@ static Node *build_list_comprehension_node(char *var_name, Node *expr,
/* build the UNWIND node */
unwind = make_ag_node(cypher_unwind);
unwind->target = res;

/*
* We need to make a ColumnRef of var_name so that it can be used as an expr
* for the where clause part of unwind.
*/
cref = makeNode(ColumnRef);
cref->fields = list_make1(makeString(var_name));
cref->location = var_loc;

unwind->where = where;

/* if there is a mapping function, add its arg to collect */
Expand Down
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