Array support for Hplsql.g4 or Hive.g4 - hive

Question

Good day everyone,
I am using antlr4 to create a parser and lexer for Hive SQL (Hplsql.g4).
I believe this is the latest grammar file.
https://github.com/AngersZhuuuu/Spark-Hive/blob/master/hplsql/src/main/antlr4/org/apache/hive/hplsql/Hplsql.g4
However, I found at least two additions that are needed: IF and array indices.
For example, in a select statement, I may have:
a) SELECT if(a>8,12,20) FROM x
b) SELECT column_name[2] FROM x
Both are valid in Hive but both do not parse when I create a parser and lexer for java from the Hplsql.g4 above. I added an expression for the IF and it appears to work.
I added
expr :
...
| expr_if //I added
and a new rule:
expr_if :
T_IF T_OPEN_P bool_expr T_COMMA expr T_COMMA expr T_CLOSE_P //I added
;
However, figuring out how to allow an array index is not so easy because the grammar allows aliases:
select a from x
select a alias_of_a from x
select a[1] from x
select a[1] alias_of_a from x
should all be valid.
I tried adding a new expression for this like so:
expr :
...
| expr_array //I added
expr_array :
T_OPEN_SB L_INT T_OPEN_CB //I added
;
This didn't work for me. (T_OPEN_SB L_INT T_OPEN_CB are [ integer ] respectively). I tried so many variations on this as well. My questions are:
Am I using the right grammar file - if not is there a newer one with IF and array handling?
Has anyone been successful in extending this grammar to handle my cases above?
As per Bart's recommendations:
I updated ident.
I updated expr_atom.
I added array_index.
I had // | '[' .*? ']' commented out before.
Test Sql: select a[0] from t
Result:
line 1:8 no viable alternative at input 'selecta[0]'
line 1:8 mismatched input '[0]'
Tree
(program (block stmt (stmt select) (stmt (expr_stmt (expr (expr_atom (ident a)))))) [0] from t)
I feel like the problem is somehow related to select_list_alias below.
With select_list_alias containing ident and T_AS optional, ident is matching the array index.
I can't reconcile why this happens, especially since ident has been updated.
Excerpt from Hplsql.sql:
select_list :
select_list_set? select_list_limit? select_list_item (T_COMMA select_list_item)*
;
select_list_item :
(ident T_EQUAL)? expr select_list_alias?
| select_list_asterisk
;
select_list_alias :
{!_input.LT(1).getText().equalsIgnoreCase("INTO") && !_input.LT(1).getText().equalsIgnoreCase("FROM")}? T_AS? ident
| T_OPEN_P T_TITLE L_S_STRING T_CLOSE_P
;
If I pass in a simple SQL stmt to grun such as
select a[1] from t
The parse tree should look similar to this:
Instead of expr_atom, I want to see expr_array where it would split into expr_atom for the a and array_index for the [1].
Note that there is one SQL statement here. With my existing g4, the array index [1] (and the remainder of the stmt) gets parsed as a separate SQL statement.
Bart, I see from your parse tree that parsing resulted in two SQL statements from "select a[0] from t" - I was getting the same situation.
I will continue to explore different approaches - I am still suspicious of the select_list_alias which has T_AS? ident at the end. Just to confirm, I have commented out one line from ident_part like this: // | '[' .*? ']'

Answer 1

As mentioned in the comments: [ ... ] will be tokenised as a L_ID token. If you don;t want that, remove the | '[' .*? ']' part:
fragment
L_ID_PART :
[a-zA-Z] ([a-zA-Z] | L_DIGIT | '_')* // Identifier part
| ('_' | '#' | ':' | '#' | '$') ([a-zA-Z] | L_DIGIT | '_' | '#' | ':' | '#' | '$')+ // (at least one char must follow special char)
| '"' .*? '"' // Quoted identifiers
// | '[' .*? ']' <-- removed
| '`' .*? '`'
;
and create/edit the grammar like this:
expr_atom :
date_literal
| timestamp_literal
| bool_literal
| expr_array // <-- added
| ident
| string
| dec_number
| int_number
| null_const
;
// new rule
expr_array
: ident array_index+
;
// new rule
array_index
: T_OPEN_SB expr T_CLOSE_SB
;
The rules above will cause select a[1] alias_of_a from x to be parsed successfully, but wil fail on input like select a[1] alias_of_a from [identifier]: the [identifier] will not be matched as an identifier.
You could try adding something like this:
ident :
L_ID
| T_OPEN_SB ~T_CLOSE_SB+ T_CLOSE_SB // <-- added
| non_reserved_words
;
which will parse select a[1] alias_of_a from [identifier] properly, but have no good picture of the whole grammar (or deep knowledge of HPL/SQL) to determine if that will mess up other things :)
EDIT
With my proposed changes, the grammar looks like this: https://gist.github.com/bkiers/4aedd6074726cbcd5d87ede00000cd0d (I cannot post it here on SO because of the char limit)
Parsing select a[0] from t with this will result in the parse tree:
And parsing select a[0] from [t] with this will result in this parse tree:
You're also able to test it by running the following Java code:
String source = "select a[0] from [t]";
HplsqlLexer lexer = new HplsqlLexer(CharStreams.fromString(source));
HplsqlParser parser = new HplsqlParser(new CommonTokenStream(lexer));
ParseTree root = parser.program();
JFrame frame = new JFrame("Antlr AST");
JPanel panel = new JPanel();
TreeViewer viewer = new TreeViewer(Arrays.asList(parser.getRuleNames()), root);
viewer.setScale(1.5);
panel.add(viewer);
frame.add(panel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);