[HACKERS] Malformed Array Literal in PL/pgSQL Exception Block

[David E. Wheeler]

Hackers,

I’ve been happily using the array-to-element concatenation operator || to 
append a single value to an array, e.g, 

    SELECT array || 'foo';

And it works great, including in PL/pgSQL functions, except in an exception 
block. When I run this:

    BEGIN;

    CREATE OR REPLACE FUNCTION foo(
    ) RETURNS BOOLEAN IMMUTABLE LANGUAGE PLPGSQL AS $$
    DECLARE
        things TEXT[] := '{}';
    BEGIN
        things := things || 'foo';
        RAISE division_by_zero;
    EXCEPTION WHEN OTHERS THEN
        things := things || 'bar';
    END;
    $$;

    SELECT foo();

    ROLLBACK;

The output is:

    psql:array.sql:15: ERROR:  malformed array literal: "bar"
    LINE 1: SELECT things || 'bar'
                             ^
    DETAIL:  Array value must start with "{" or dimension information.
    QUERY:  SELECT things || 'bar'
    CONTEXT:  PL/pgSQL function foo() line 8 at assignment

Note that it’s fine with the use of || outside the exception block, but not 
inside! I’ve worked around this by using `things || '{bar}'` instead, but it 
seems like a bug or perhaps unforeseen corner case that appending a value to an 
array doesn’t work in an exception-handling block.

Best,

David

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