E08086: condition is always true based on data flow analysis

What went wrong

This condition is always true based on the values assigned to variables on this code path. The compiler tracks variable assignments and can determine that this comparison will always produce the same result, making the else/default branch unreachable dead code.

A guard over a Boolean is a truth guard: in an 'if' / 'else if', 'if ok <- check()' enters only when ok is SET AND TRUE. So its gate is a condition too: 'if ok <- true' always enters, and 'then ok' after such a guard is always true - the gate already required it.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 796 (Why does EK9 reject comparisons against variables with kn...)

How to fix it

1. Remove the redundant condition and its else/default branch
2. If the condition is needed on some paths, restructure the logic
3. Check if a variable was intended to be reassigned before this check
4. Verify this isn't a copy-paste error from a similar condition

Common causes

• Variable assigned a literal and then immediately compared to that literal
• Applies to all literal types: Integer, Float, Character, String, Date, Time, DateTime, Millisecond
• Outer condition already implies the inner condition
• Redundant defensive check after a known assignment
• Refactoring left behind a condition that is no longer needed
• 'if ok <- check() then ok' — the Boolean guard already enters only when ok is true
• A Boolean guard over a value known to be true: 'if ready <- true'

See also

• E08082: comparison between literal values (both operands are literals)
• E08087: condition always false (dead if-body instead of dead else)
• E08085: logical tautology (structural pattern like 'a or not a')

Examples

Every example is compiled by the EK9 compiler: the first fails exactly as captioned, the others fix it.

Fails with E08086: condition is always true based on data flow analysis

#!ek9
defines module error.e08086.bad

  defines constant
    MANY <- 10
    SEVERAL <- 6

  defines function

    classify()
      -> count as Integer
      <- rtn as String: "few"
      if count > MANY
        if count > SEVERAL
          rtn: "many"

    describe()
      <- rtn as String: "unknown"
      enabled <- false
      if not enabled
        rtn: "disabled"

Fixed: Test only what is not already known

#!ek9
defines module error.e08086.good

  defines constant
    MANY <- 10

  defines function

    classify()
      -> count as Integer
      <- rtn as String: "few"
      if count > MANY
        rtn: "many"

    describe()
      -> enabled as Boolean
      <- rtn as String: "enabled"
      if not enabled
        rtn: "disabled"

Questions and answers

These Q&A entries show E08086 and its fix:

• Q796: Why does EK9 reject comparisons against variables with known constant values?