fix: use || instead of ?? for CLI flag override precedence in preparse hook

[jon-freed]

What does this PR do?

Fixes a bug where CLI arguments fail to override --flags-dir values in certain scenarios. The bug is in the tpreparse hook where it is using ?? (nullish coalescing) instead of || (logical OR) when checking if a CLI flag was already present.

Bug Details

Introduced in: Commit c83f81a (2025-04-22, "chore: bump wireit, fix types")

Affected versions: SF CLI 2.100.0 through 2.120.x

The change added a necessary guard (flagOptions.char &&) to prevent checking for undefined short chars, but incorrectly used ?? instead of || to chain conditions:

// Before c83f81a (correct):
argv.includes(`-${flagOptions.char}`) ||
argv.includes(`--${flagName}`) ||

// After c83f81a (buggy):
(flagOptions.char && argv.includes(`-${flagOptions.char}`)) ??
argv.includes(`--${flagName}`) ??

Since ?? only evaluates the right side when left is null/undefined, and false is neither, the long-form check was skipped when the short-char check returned false.

Affected Scenarios

The bug affects scenarios where:

• A flag has a short char defined (e.g., { char: 'l' } for --test-level)
• The user invokes the long form on CLI (e.g., --test-level instead of -l)
• The same flag exists in --flags-dir

Example:

# flags-dir/test-level contains: NoTestRun
# User wants to override with RunLocalTests:
sf project deploy start --flags-dir ./flags --test-level RunLocalTests

# Expected: RunLocalTests wins (CLI overrides flags-dir)
# With bug: Error "Flag --test-level can only be specified once"

5 specific scenarios are affected (out of 14 tested):

1. String flag with char, CLI uses long form
2. Boolean flag with char, CLI uses long form
3. Boolean allowNo flag (no char), CLI uses --no-<flag> form
4. Boolean allowNo with char, CLI uses --<flag> long form
5. Boolean allowNo with char, CLI uses --no-<flag> long form

Root Cause

The ESLint rule @typescript-eslint/prefer-nullish-coalescing likely suggested the change from || to ??, but the rule's advice was incorrect in this context. The fix includes an eslint-disable comment to prevent this from recurring.

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Acceptance Criteria

• CLI arguments properly override --flags-dir values as documented in PR feat: add preparse hook for --flags-dir #1536
• Multiple-value flags still combine CLI and file values (unchanged behavior)
• Comprehensive tests cover all flag type / char config / CLI form combinations
• All existing tests continue to pass

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Testing Notes

Added systematic tests organized by:

• [A] Flag type: String single, String multiple, Boolean, Boolean allowNo
• [B] Short char config: No char vs has char
• [C] CLI invocation: Short form vs long form

The tests verify the documented behavior from PR #1536:

"Flags/values provided by the user will override any flag/values found by --flags-dir -- unless the flag supports multiple, in which case they will all be combined."

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Checklist

• This is a bug fix restoring documented behavior from PR feat: add preparse hook for --flags-dir #1536
• No deprecation policy concerns - this is a pure bug fix

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What issues does this PR fix or reference?

Fixes forcedotcom/cli#3486

Fixes regression introduced in c83f81a. Restores the behavior documented in PR #1536.