LoopConditionChecker fails to resolve compile-time constant loop bounds, missing genuine infinite loops #5826

Error Prone version

Error Prone 2.49.0 (javac plugin) — javac 21.0.8, source/target 21.

Check name

LoopConditionChecker

Description

LoopConditionChecker flags loops whose condition variable(s) are never modified in the loop body (a no-op or infinite loop). The check is sensitive to the syntactic form of the loop bound rather than its compile-time-constant value: replacing the literal 1 with a static final int ONE = 1 — which javac inlines as the constant 1 — silences the diagnostic, even though the loop is byte-for-byte identical at runtime and is still an infinite loop.

Reproducer

// BEFORE — LoopConditionChecker fires on the second loop
class C {
  void foo() {
    for (int i = 0; i < 1; i++) {}      // i is modified -> not flagged
    for (int i = 0; i < 1; foo()) {}    // i never modified -> FLAGGED
  }
}

// AFTER — semantically identical (ONE is the constant 1), rule no longer fires
class C { static final int ONE = 1;
  void foo() {
    for (int i = 0; i < ONE; i++) {}
    for (int i = 0; i < ONE; foo()) {}  // still an infinite loop, NOT flagged
  }
}

Expected behavior

LoopConditionChecker should report the same finding on BEFORE and AFTER. ONE is a compile-time constant equal to 1, so i < ONE and i < 1 are identical, and the second loop is an infinite loop in both forms.

Actual behavior

• BEFORE: 1 finding — condition variable(s) never modified in loop body: i on the for (int i = 0; i < 1; foo()) loop.
• AFTER: 0 findings. The checker bails out once the bound is a named constant instead of a literal, failing to constant-fold the condition operand.