Repository: tobymao/sqlglot

Issue:
Trino CURRENT_USER does not allow parenthesis
```python
from sqlglot import parse_one
from sqlglot.dialects import Trino

sql_in = parse_one("SELECT CURRENT_USER", dialect=Trino)
print(sql_in.sql(dialect=Trino))
```
```bash
SELECT CURRENT_USER()
```

https://prestodb.io/docs/current/functions/session.html
https://trino.io/docs/current/functions/session.html

I believe that the Postgres dialect already implements the desired workaround for this function
https://github.com/tobymao/sqlglot/blob/v25.32.1/sqlglot/dialects/postgres.py#L527

Hints from issue comments:
@MikeWallis42: If I may, I would like to submit the solution for this given that it's an easier entry point in to contributing@VaggelisD: Sure, please go for it @MikeWallis42! Thank you.

Solution patch:
diff --git a/sqlglot/dialects/bigquery.py b/sqlglot/dialects/bigquery.py
index 2f3ac53efb..ec8188bb7c 100644
--- a/sqlglot/dialects/bigquery.py
+++ b/sqlglot/dialects/bigquery.py
@@ -319,7 +319,7 @@ def _builder(args: t.List) -> exp.TimeToStr:
 
 def _build_contains_substring(args: t.List) -> exp.Contains | exp.Anonymous:
     if len(args) == 3:
-        return exp.Anonymous(this="CONTAINS_SUBSTRING", expressions=args)
+        return exp.Anonymous(this="CONTAINS_SUBSTR", expressions=args)
 
     # Lowercase the operands in case of transpilation, as exp.Contains
     # is case-sensitive on other dialects
@@ -492,7 +492,7 @@ class Parser(parser.Parser):
 
         FUNCTIONS = {
             **parser.Parser.FUNCTIONS,
-            "CONTAINS_SUBSTRING": _build_contains_substring,
+            "CONTAINS_SUBSTR": _build_contains_substring,
             "DATE": _build_date,
             "DATE_ADD": build_date_delta_with_interval(exp.DateAdd),
             "DATE_SUB": build_date_delta_with_interval(exp.DateSub),
@@ -1219,4 +1219,4 @@ def contains_sql(self, expression: exp.Contains) -> str:
                 this = this.this
                 expr = expr.this
 
-            return self.func("CONTAINS_SUBSTRING", this, expr)
+            return self.func("CONTAINS_SUBSTR", this, expr)
diff --git a/sqlglot/dialects/presto.py b/sqlglot/dialects/presto.py
index 056d974c27..a87a5fce00 100644
--- a/sqlglot/dialects/presto.py
+++ b/sqlglot/dialects/presto.py
@@ -376,6 +376,7 @@ class Generator(generator.Generator):
             exp.Cast: transforms.preprocess([transforms.epoch_cast_to_ts]),
             exp.CurrentTime: lambda *_: "CURRENT_TIME",
             exp.CurrentTimestamp: lambda *_: "CURRENT_TIMESTAMP",
+            exp.CurrentUser: lambda *_: "CURRENT_USER",
             exp.DateAdd: _date_delta_sql("DATE_ADD"),
             exp.DateDiff: lambda self, e: self.func(
                 "DATE_DIFF", unit_to_str(e), e.expression, e.this


Test patch:
diff --git a/tests/dialects/test_bigquery.py b/tests/dialects/test_bigquery.py
index 26b12a15fa..09f7673cef 100644
--- a/tests/dialects/test_bigquery.py
+++ b/tests/dialects/test_bigquery.py
@@ -1608,11 +1608,11 @@ def test_bigquery(self):
         )
 
         self.validate_identity(
-            "CONTAINS_SUBSTRING(a, b, json_scope => 'JSON_KEYS_AND_VALUES')"
+            "CONTAINS_SUBSTR(a, b, json_scope => 'JSON_KEYS_AND_VALUES')"
         ).assert_is(exp.Anonymous)
 
         self.validate_all(
-            """CONTAINS_SUBSTRING(a, b)""",
+            """CONTAINS_SUBSTR(a, b)""",
             read={
                 "": "CONTAINS(a, b)",
                 "spark": "CONTAINS(a, b)",
@@ -1628,7 +1628,7 @@ def test_bigquery(self):
                 "snowflake": "CONTAINS(LOWER(a), LOWER(b))",
                 "duckdb": "CONTAINS(LOWER(a), LOWER(b))",
                 "oracle": "CONTAINS(LOWER(a), LOWER(b))",
-                "bigquery": "CONTAINS_SUBSTRING(a, b)",
+                "bigquery": "CONTAINS_SUBSTR(a, b)",
             },
         )
 
diff --git a/tests/dialects/test_presto.py b/tests/dialects/test_presto.py
index c0870895e3..f39a0d5ef5 100644
--- a/tests/dialects/test_presto.py
+++ b/tests/dialects/test_presto.py
@@ -1071,6 +1071,18 @@ def test_presto(self):
                 "databricks": "REGEXP_EXTRACT('abc', '(a)(b)(c)', 0)",
             },
         )
+        self.validate_all(
+            "CURRENT_USER",
+            read={
+                "presto": "CURRENT_USER",
+                "trino": "CURRENT_USER",
+                "snowflake": "CURRENT_USER()",  # Although the ANSI standard is CURRENT_USER
+            },
+            write={
+                "trino": "CURRENT_USER",
+                "snowflake": "CURRENT_USER()",
+            },
+        )
 
     def test_encode_decode(self):
         self.validate_identity("FROM_UTF8(x, y)")