Mao Jiayi created FLINK-40337:
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Summary: Preserve operator precedence in generated Janino
expressions
Key: FLINK-40337
URL: https://issues.apache.org/jira/browse/FLINK-40337
Project: Flink
Issue Type: Bug
Components: Flink CDC
Reporter: Mao Jiayi
When Flink CDC translates a Pipeline transform expression from Calcite SQL
nodes to Janino code, {{JaninoCompiler}} constructs {{Java.BinaryOperation}}
nodes and serializes them via {{Java.Rvalue#toString()}}. This method
concatenates operands directly without considering operator precedence, so
parentheses present in the original expression are silently dropped.
For example, the following expressions all change semantics after code
generation:
{code}
(a + b) * c → a + b * c
(a OR b) AND c → a || b && c
a / (b * c) → a / b * c
a - (b - c) → a - b - c
{code}
The generated Janino code evaluates with different grouping than the user's
original transform expression, producing incorrect results without any error or
warning. Expressions without nesting are unaffected.
*Expected behavior*: the generated code preserves the original expression's
semantics — parentheses are retained where grouping matters, and omitted where
precedence already guarantees correct evaluation order (e.g. {{a + b * c}}
should stay as-is).
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