Change plpgsql from using textual substitution to insert variable references

into SQL expressions, to using the newly added parser callback hooks.

This allows us to do the substitutions in a more semantically-aware way:
a variable reference will only be recognized where it can validly go,
ie, a place where a column value or parameter would be legal, instead of
the former behavior that would replace any textual match including
table names and column aliases (leading to syntax errors later on).
A release-note-worthy fine point is that plpgsql variable names that match
fully-reserved words will now need to be quoted.

This commit preserves the former behavior that variable references take
precedence over any possible match to a column name.  The infrastructure
is in place to support the reverse precedence or throwing an error on
ambiguity, but those behaviors aren't accessible yet.

Most of the code changes here are associated with making the namespace
data structure persist so that it can be consulted at runtime, instead
of throwing it away at the end of initial function parsing.

The plpgsql scanner is still doing name lookups, but that behavior is
now irrelevant for SQL expressions.  A future commit will deal with
removing unnecessary lookups.

2 files changed, 76 insertions, 2 deletions

diff --git a/src/test/regress/expected/plpgsql.out b/src/test/regress/expected/plpgsql.out
index 2e97bec42e9..5846246b7c2 100644
--- a/src/test/regress/expected/plpgsql.out
+++ b/src/test/regress/expected/plpgsql.out
@@ -899,7 +899,7 @@ begin
         declare
 	    rec		record;
 	begin
-	    select into rec * from PLine where slotname = outer.rec.backlink;
+	    select into rec * from PLine where slotname = "outer".rec.backlink;
 	    retval := ''Phone line '' || trim(rec.phonenumber);
 	    if rec.comment != '''' then
 	        retval := retval || '' ('';
@@ -3938,3 +3938,43 @@ LINE 1:  SELECT rtrim(roomno) AS roomno, foo FROM Room ORDER BY room...
                                          ^
 QUERY:   SELECT rtrim(roomno) AS roomno, foo FROM Room ORDER BY roomno
 CONTEXT:  PL/pgSQL function "inline_code_block" line 3 at FOR over SELECT rows
+-- Check variable scoping -- a var is not available in its own or prior
+-- default expressions.
+create function scope_test() returns int as $$
+declare x int := 42;
+begin
+  declare y int := x + 1;
+          x int := x + 2;
+  begin
+    return x * 100 + y;
+  end;
+end;
+$$ language plpgsql;
+select scope_test();
+ scope_test 
+------------
+       4443
+(1 row)
+
+drop function scope_test();
+-- Check handling of conflicts between plpgsql vars and table columns.
+create function conflict_test() returns setof int8_tbl as $$
+declare r record;
+  q1 bigint := 42;
+begin
+  for r in select q1,q2 from int8_tbl loop
+    return next r;
+  end loop;
+end;
+$$ language plpgsql;
+select * from conflict_test();
+ q1 |        q2         
+----+-------------------
+ 42 |               456
+ 42 |  4567890123456789
+ 42 |               123
+ 42 |  4567890123456789
+ 42 | -4567890123456789
+(5 rows)
+
+drop function conflict_test();
diff --git a/src/test/regress/sql/plpgsql.sql b/src/test/regress/sql/plpgsql.sql
index 83cda97d1bf..51bfce2e0c1 100644
--- a/src/test/regress/sql/plpgsql.sql
+++ b/src/test/regress/sql/plpgsql.sql
@@ -1026,7 +1026,7 @@ begin
         declare
 	    rec		record;
 	begin
-	    select into rec * from PLine where slotname = outer.rec.backlink;
+	    select into rec * from PLine where slotname = "outer".rec.backlink;
 	    retval := ''Phone line '' || trim(rec.phonenumber);
 	    if rec.comment != '''' then
 	        retval := retval || '' ('';
@@ -3135,3 +3135,37 @@ BEGIN
         RAISE NOTICE '%, %', r.roomno, r.comment;
     END LOOP;
 END$$;
+
+-- Check variable scoping -- a var is not available in its own or prior
+-- default expressions.
+
+create function scope_test() returns int as $$
+declare x int := 42;
+begin
+  declare y int := x + 1;
+          x int := x + 2;
+  begin
+    return x * 100 + y;
+  end;
+end;
+$$ language plpgsql;
+
+select scope_test();
+
+drop function scope_test();
+
+-- Check handling of conflicts between plpgsql vars and table columns.
+
+create function conflict_test() returns setof int8_tbl as $$
+declare r record;
+  q1 bigint := 42;
+begin
+  for r in select q1,q2 from int8_tbl loop
+    return next r;
+  end loop;
+end;
+$$ language plpgsql;
+
+select * from conflict_test();
+
+drop function conflict_test();