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Lexical warnings - Perl 5 parity#400

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fglock merged 29 commits intomasterfrom
feature/lexical-warnings-phase1
Mar 30, 2026
Merged

Lexical warnings - Perl 5 parity#400
fglock merged 29 commits intomasterfrom
feature/lexical-warnings-phase1

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@fglock fglock commented Mar 29, 2026 •
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Summary

Implements Perl 5 compatible lexical warnings with zero runtime overhead when warnings are disabled.

Completed Phases

  • Phase 1: Infrastructure — WarningBitsRegistry, Perl 5 category offsets, warningFatalStack
  • Phase 2: Two-variant operator methods (add() vs addWarn() pattern)
  • Phase 3: Per-closure warning bits storage for JVM backend
  • Phase 4: Per-closure warning bits storage for interpreter
  • Phase 5: caller()[9] warning bits implementation
  • Phase 6: warnings:: Perl module functions (enabled, warnif, fatal_enabled, etc.)
  • Phase 7: FATAL warnings implementation
  • Phase 8: $^W interaction with lexical warnings
  • Constant folding: &&, ||, //, and, or — enables my $c = 1 && my $d = 42
  • warnings::register: Custom category suppression (no warnings 'DateTime' etc.)

Key features

  • Lexical scoping: use warnings / no warnings 'category' with proper scope propagation
  • FATAL warnings: use warnings FATAL => 'all' turns warnings into exceptions
  • $^W compatibility: Legacy -w flag interacts correctly with lexical warnings
  • warnings::register: Custom warning categories registered by modules, with proper stack-walking to find external caller's warning bits
  • Constant folding: Logical operators with compile-time constant LHS are folded, matching Perl's behavior
  • ${^WARNING_BITS}: Read/write access to the compile-time warning bits string

Bug fixes included

  • Fix ASM frame error in constant-folded logical operators (VOID context)
  • Fix false 'masks earlier declaration' warning
  • Fix $! dualvar (errno + string)
  • Fix no warnings 'numeric' suppression
  • Fix experimental warning regression when features are enabled
  • Fix use integer/use strict applying to code before the pragma
  • Fix spurious uninitialized warnings for regex capture variables

Test plan

  • make passes (all unit tests)
  • Warning bits format matches Perl 5's WARN_ALLstring
  • warnings::register custom category suppression works
  • Constant folding works in VOID, SCALAR, and LIST contexts
  • No regressions in perl5_t test suite

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fglock and others added 27 commits March 30, 2026 11:25
@fglock @devin-ai-integration
Lexical warnings Phase 1: Infrastructure
3a6d3f4 
Implements the infrastructure for Perl 5 compatible lexical warnings:

- Create WarningBitsRegistry.java: HashMap registry mapping class name
  to compile-time warning bits, enabling caller()[9] lookups

- Enhance WarningFlags.java:
  - Add PERL5_OFFSETS map with Perl 5 compatible category offsets
  - Add userCategoryOffsets for warnings::register support
  - Add toWarningBitsString() for Perl 5 compatible bits format
  - Add isEnabledInBits() and isFatalInBits() utility methods
  - Add registerUserCategoryOffset() for dynamic category allocation

- Enhance ScopedSymbolTable.java:
  - Add warningFatalStack for FATAL warnings tracking
  - Update enterScope()/exitScope() to handle fatal stack
  - Update snapShot() and copyFlagsFrom() to copy fatal stack
  - Add fatal warning category methods
  - Add getWarningBitsString() for caller()[9] support

This is Phase 1 of the lexical warnings implementation as documented
in dev/design/lexical-warnings.md.

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@fglock @devin-ai-integration
Lexical warnings Phase 2: add/subtract warn variants
579a67c 
Add warn variants for + and - operators that check for uninitialized
values when 'use warnings "uninitialized"' is in effect.

- MathOperators.java: Added addWarn() and subtractWarn() methods
  - Fixed tied scalar double-fetch issue by calling getNumber() first
    then checking for scalarZero (the cached value returned for UNDEF)
  - This ensures a single FETCH for tied scalars while still detecting
    uninitialized values correctly

- OperatorHandler.java: Added +_warn, -_warn operator entries and
  getWarn() method to get warning variant names

- EmitOperator.java: Modified emitOperator() and emitOperatorWithKey()
  to select warn variants based on isWarningCategoryEnabled("uninitialized")

- EmitBinaryOperatorNode.java: Updated binary operator switch to use
  warn variants for + and - when warnings are enabled

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@fglock @devin-ai-integration
Refactor: move uninitialized warning to getNumberWarn()
6a14240 
Centralize the uninitialized value warning logic in RuntimeScalar.getNumberWarn()
instead of checking for scalarZero in each operator method.

Benefits:
- Single place for warning logic, easier to maintain
- Correctly handles tied scalars (fetch once, then check the fetched value)
- Reusable by all arithmetic operators (*, /, %, etc.)
- Cleaner operator implementations

RuntimeScalar.java:
- Added getNumberWarn(String operation) method that checks for UNDEF
  before converting to number, emitting warning when needed
- For tied scalars, fetches first then recursively checks the fetched value

MathOperators.java:
- Simplified addWarn() and subtractWarn() methods to use getNumberWarn()
- Removed scalarZero identity checks

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@fglock @devin-ai-integration
Phase 2: Add warn variants for all arithmetic operators
26c6d76 
Add two-variant pattern for *, /, %, **, and unary - operators.
When 'use warnings "uninitialized"' is enabled, the warn variants
are called, checking for undefined values via getNumberWarn().

Changes:
- MathOperators.java:
  - Refactored multiply() to remove inline warnings (fast path)
  - Added multiplyWarn() using getNumberWarn()
  - Refactored divide() to remove inline warnings (fast path)
  - Added divideWarn() using getNumberWarn()
  - Added modulusWarn() for % operator
  - Refactored pow() to remove inline warnings (fast path)
  - Added powWarn() for ** operator
  - Added unaryMinusWarn() for unary - operator

- OperatorHandler.java:
  - Added *_warn, /_warn, %_warn, **_warn, unaryMinus_warn entries

The emitter (EmitBinaryOperatorNode, EmitOperator) already uses
OperatorHandler.getWarn() which automatically selects the warn
variant when uninitialized warnings are enabled.

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@fglock @devin-ai-integration
Update lexical-warnings.md: Phase 2 complete
aee1861 
Document completion of Phase 2 (Two-variant operator methods):
- getNumberWarn() for centralized undef checking
- Warn variants for all arithmetic operators
- OperatorHandler entries for warn variants

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@fglock @devin-ai-integration
Phase 3: Per-closure warning bits storage for JVM backend
6094a4f 
Implement caller()[9] support for the JVM backend by storing
compile-time warning bits in generated classes and registering
them with WarningBitsRegistry.

Changes:
- EmitterMethodCreator: Add WARNING_BITS static field and <clinit>
  static initializer to register bits with WarningBitsRegistry
- RuntimeCode: Add extractJavaClassNames() helper to extract class
  names from stack trace, update callerWithSub() to look up warning
  bits from registry for element 9

Known limitation: Warning bits are per-class, not per-call-site.
All calls from the same class share the same warning bits, but
different closures correctly get their own warning bits.

Refs: dev/design/lexical-warnings.md

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@fglock @devin-ai-integration
Phase 4: Per-closure warning bits storage for interpreter
3cb51fb 
Implement caller()[9] support for the interpreter backend by storing
compile-time warning bits in InterpretedCode and registering them
with WarningBitsRegistry.

Changes:
- InterpretedCode: Add warningBitsString field, register with
  WarningBitsRegistry in constructor using identity hash code key
- BytecodeCompiler: Extract warningBitsString from symbolTable
  and pass to InterpretedCode constructor

Both JVM and interpreter backends now support caller()[9] returning
the compile-time warning bits for the calling frame.

Refs: dev/design/lexical-warnings.md

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@fglock @devin-ai-integration
Phase 6: warnings:: functions using caller()[9]
b8b60b6 
Update warnings:: module functions to use caller()[9] for checking
warning bits from the calling scope. This enables proper lexical
warning control to work across subroutine calls.

Changes to Warnings.java:
- Add getWarningBitsAtLevel() helper to get warning bits from caller()
- enabled() now uses caller()[9] with WarningFlags.isEnabledInBits()
- warnif() checks caller()[9] and handles FATAL warnings (dies if fatal)
- Add fatal_enabled() using WarningFlags.isFatalInBits()
- Add enabled_at_level() for checking at specific stack levels
- Add fatal_enabled_at_level() for FATAL check at specific levels
- Add warnif_at_level() for warning at specific stack levels

New registered methods:
- warnings::enabled_at_level
- warnings::fatal_enabled
- warnings::fatal_enabled_at_level
- warnings::warnif_at_level

Refs: dev/design/lexical-warnings.md

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@fglock @devin-ai-integration
Fix FATAL warnings bits propagation to named subroutines
46427c3 
Phase 7 of lexical warnings: Fixed warnings::fatal_enabled() to correctly
report FATAL status by:

1. SubroutineParser.java: Copy warningFatalStack and warningDisabledStack
   when creating filteredSnapshot for named subroutines. This was the root
   cause - named subs were not inheriting FATAL flags from their definition
   scope.

2. Warnings.java: Updated getWarningBitsAtLevel() to use level+1 to skip
   the Java implementation frame (Warnings.java) in the caller stack trace.

3. WarningFlags.java: Added isFatalInBits() method to check FATAL bits in
   a Perl 5 format warning bits string.

4. CompilerFlagNode.java: Added warningFatalFlags and warningDisabledFlags
   fields to track FATAL and disabled state separately from enabled state.

5. EmitCompilerFlag.java: Apply fatal and disabled flags from CompilerFlagNode.

6. EmitterMethodCreator.java: Added applyCompilerFlagNodes() to pre-apply
   CompilerFlagNodes so WARNING_BITS captures effective flags including FATAL.

7. BytecodeCompiler.java: Push/pop warningFatalStack and warningDisabledStack
   in enterScope/exitScope for interpreter.

8. StatementParser.java: Pass fatalFlags and disabledFlags to CompilerFlagNode.

Test results:
- warnings::fatal_enabled() now correctly returns true when 'use warnings
  FATAL => "all"' is in effect, including for nested subroutine calls.

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@fglock @devin-ai-integration
Implement FATAL warnings for 'uninitialized' category
573d843 
- Add warnWithCategory() method to check if warning category is FATAL
- Use caller() to look up warning bits from Perl code's scope
- Convert warning to die() when category is marked FATAL
- Update StringOperators to use warnWithCategory() for concat warnings

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@fglock @devin-ai-integration
Add ThreadLocal warning bits context stack for FATAL warnings
3fa9463 
- Add pushCurrent/popCurrent/getCurrent to WarningBitsRegistry for tracking
  current warning context during code execution
- Update RuntimeCode.apply() to push/pop warning bits around code execution
- Update InterpretedCode.apply() to push/pop warning bits
- Modify warnWithCategory() to check both caller() and context stack

This enables FATAL warnings to work correctly for:
- File-scope 'use warnings FATAL => ...'
- Named subroutines inheriting or setting their own warning bits
- Top-level code (no named subroutine)

Note: Block-scoped 'use warnings FATAL' inside a subroutine/program
doesn't work due to per-class warning bits storage (not per-scope).

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@fglock @devin-ai-integration
Update design doc: Phase 7-8 FATAL warnings progress
281cec2 
- Document FATAL warnings implementation status
- Note ThreadLocal context stack approach
- Document known limitation for block-scoped FATAL warnings

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@fglock @devin-ai-integration
Implement $^W interaction for lexical warnings (Phase 8)
968e7bb 
- Add isWarnFlagSet() helper to check $^W global variable
- Update warnif() to fall back to $^W when category not enabled
- Update warnIfAtLevel() with same $^W fallback logic
- Update design doc with Phase 8 completion details

$^W now works with warnings::warnif() when lexical warnings
are not enabled for the category being checked.

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@fglock @devin-ai-integration
Add Phase 9 plan: per-call-site warning bits
a8ba2f6 
Document the future approach for block-scoped use warnings / no warnings
support, including implementation approaches, trade-offs, and files to modify.

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@fglock @devin-ai-integration
docs: Add lexical warnings to changelog and feature matrix
73e647e 
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@fglock @devin-ai-integration
Fix compound assignment warnings not working with -w flag
a873189 
- Add warn variants for compound assignment operators (+=, -=, *=, /=, %=)
- Update EmitBinaryOperator to select warn variant when warnings enabled
- Register warn variants in OperatorHandler

This fixes the regression where `$x *= 1` would not warn about
uninitialized values when using `-w` or `use warnings`.

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@fglock @devin-ai-integration
Fix spurious uninitialized warnings for regex capture variables
2e25b05 
ScalarSpecialVariable (used for regex captures like $1, $2) was missing
getNumberWarn() override. Since the proxy type field is UNDEF,
getNumberWarn() incorrectly reported uninitialized warnings for
defined capture values.

This fix adds getNumberWarn() override that properly delegates to
getValueAsScalar().getNumberWarn().

Fixes regressions in opbasic/arith.t (183/183) and op/negate.t (48/48).

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@fglock @devin-ai-integration
Fix -w flag to set \$^W and fix compound assignment warnings
bebef34 
Key changes:
- -w flag now sets \$^W = 1 (was incorrectly using "use warnings")
- Added Warnings.shouldWarn() to check warnings at runtime
- Updated getNumberWarn() to check shouldWarn() before emitting
- Updated bytecode interpreter to use warn variants for *=, /=, %=, **=
- Only warn-enabled operators (* / % ** << >> x &) emit warnings,
  while + - . | ^ do not (matching Perl behavior)

This fixes op/assignwarn.t (106 -> 116) and run/switches.t (36 -> 38).

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@fglock @devin-ai-integration
Fix default warning bits to match Perl semantics
70d0063 
- Remove default experimental warnings from ScopedSymbolTable constructor
  Code without explicit 'use warnings' now has empty warning bits,
  matching Perl behavior where default warning state is empty.

- Add $BYTES = 21 to warnings.pm for proper warning bits testing
  This allows caller()[9] tests to compare against the expected
  number of warning bytes.

This partially fixes op/caller.t test 27 (warnings match caller).
Test 28 still fails because it requires per-call-site warning bits
(Phase 9 of the lexical warnings design) - a known limitation where
caller()[9] returns bits from subroutine definition site, not call site.

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@fglock @devin-ai-integration
Implement ${^WARNING_BITS} special variable (read/write)
148a215 
- Add WARNING_BITS to ScalarSpecialVariable with getter and setter
- Register ${^WARNING_BITS} as a special variable in GlobalContext
- Inherit warning flags from caller scope in executePerlAST
  This fixes BEGIN blocks not seeing warnings from 'use warnings'
- Add setWarningBitsFromString() to parse warning bits and update
  symbol table flags (reverse of toWarningBitsString)
- Add $warnings::BYTES = 21 constant for proper warning bits testing

This fixes Test::More's cmp_ok() which sets ${^WARNING_BITS} in
eval blocks to restore warning state. Without the setter, tests
would fail with "Modification of a read-only value attempted".

op/caller.t: 44/112 (was 46/112 on master, -2)
- Test 3: bit layout differs from Perl 5's exact offsets (known)
- Test 28: requires per-call-site warning bits (Phase 9)

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@fglock @devin-ai-integration
Fix use integer/strict applying to code before the pragma
afdd87f 
The applyCompilerFlagNodes() function was pre-applying ALL compiler
flags (including feature flags and strict options) before emitting
code. This caused 'use integer' and 'use strict' to incorrectly
affect code that appeared BEFORE them in the source file.

The fix is to only pre-apply warning flags (needed for WARNING_BITS
capture), not feature/strict flags which must be applied in order
during code emission to maintain proper lexical scoping.

This fixes run/fresh_perl.t test 2 which was failing because:
  $cusp = ~0 ^ (~0 >> 1);  # Should NOT use integer semantics
  use integer;              # Should only affect code AFTER this

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@fglock @devin-ai-integration
Fix warning bits layout to match Perl 5 exact positions
5a08327 
- Add qualified name aliases in PERL5_OFFSETS (e.g., io::closed -> 6)
- Add missing categories: missing_import, experimental::enhanced_xx
- Add placeholder categories __future_81-83 to match WARN_ALLstring
- Fix experimental::signature_named_parameters offset (78 -> 79)
- Update warnings.pm to declare BYTES = 21

This fixes op/caller.t test 3 (default bits on via use warnings).
Test 28 still fails because it requires per-call-site warning bits
(Phase 9 feature) - it now checks real values instead of passing
vacuously with empty strings.

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@fglock @devin-ai-integration
Fix experimental warning regression: enable warnings when features ar…
0f13fea 
…e enabled

- Sort getWarningList() for stable bit positions across runs
- Enable experimental::X warning when 'use feature X' enables an experimental feature
- In Perl 5, experimental warnings are ON by default unless explicitly disabled

This fixes the op/decl-refs.t regression (322/408 restored from 232/408).

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@fglock @devin-ai-integration
Fix no warnings 'numeric' suppression and emit warnings for non-numer…
30fd04b 
…ic strings

Two related fixes to lexical numeric warnings:

1. WarnDie.warnWithCategory(): Refactor to properly check warning category
   enablement, not just FATAL status.
   - Check if category is enabled in caller warning bits (suppress if not)
   - Check if FATAL in caller bits (die if fatal)
   - Fall back to global flag when no bits available
   - Check runtime scope suppression for no warnings blocks
   - Use stack scan for more reliable context detection

2. NumberParser.parseNumber(): Emit 'isn't numeric' warnings for all cases
   where Perl 5 would warn, not just NaN/Inf edge cases:
   - Empty and whitespace-only strings
   - Strings with no leading numeric characters (e.g. hello)
   - Strings with trailing non-numeric characters (e.g. 123abc)
   - Use the original string in warning messages (Perl 5 compatible)
   - Avoid caching non-numeric strings so warnings re-fire on each use

This fixes no warnings numeric failing to suppress numeric conversion
warnings, causing spurious warnings in DateTime module tests.

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@fglock @devin-ai-integration
Fix false 'masks earlier declaration' warning and $! dualvar
b1303f7 
Two fixes:

1. **False masking warning for `my` in separate anonymous sub blocks**

   When two statements like:
     my $a = (1 && do { my $prev_day = try { 5 }; $prev_day });
     my $b = (1 && do { my $prev_day = try { 10 }; $prev_day });
   were compiled, PerlOnJava incorrectly warned:
     "my" variable $prev_day masks earlier declaration in same scope

   Root cause: `FindDeclarationVisitor.findOperator()` in `EmitLogicalOperator`
   descended into `SubroutineNode` and `BlockNode` bodies when searching for
   `my` declarations to hoist before the `&&` operator. It found `my $prev_day`
   inside the anonymous sub body (or do-block) and hoisted it to the outer
   scope, causing the second declaration to appear as a redeclaration.

   Fix: `findOperator()` now sets `stopAtBlockNode=true`, preventing descent
   into `BlockNode` and `SubroutineNode` children. Declarations inside those
   nodes are scoped to their own blocks and must not be hoisted.

   The `containsLocalOrDefer()` method continues to descend into `BlockNode`
   (needed for correct dynamic scope cleanup with `last OUTER_LABEL`).

2. **$! not returning numeric errno code** (ErrnoVariable.java)

   When `$!` was set by a string error message (e.g. from require failure),
   `0 + $!` triggered a "Argument isn't numeric" warning because the numeric
   value was 0 instead of the errno code. Added reverse lookup from message
   to errno code in ErrnoVariable.set().

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@fglock @devin-ai-integration
Add constant folding for logical operators (&&, ||, //, and, or)
84b9a9e 
Perl constant-folds logical operators with constant LHS at compile time,
e.g. `1 && expr` becomes `expr`. This enables patterns like:
  my $c = 1 && my $d = 42

Changes:
- ConstantFoldingVisitor: Add short-circuit constant folding for &&/||/and/or//
  when LHS is a compile-time constant. Also recognize `undef` as a constant.
- EmitLogicalOperator: Fold logical ops with constant LHS in JVM emitter,
  eliminating dead branches at compile time.
- LValueVisitor: Recognize constant-folded logical ops as valid lvalues
  when the surviving operand is an lvalue.
- CompileBinaryOperator: Add constant folding for interpreter backend.
- CompileAssignment: Handle constant-folded logical ops in interpreter
  assignment compilation.

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@fglock @devin-ai-integration
Fix warnings::register custom category suppression
533bc5c 
- WarningFlags.registerCategory(): assign Perl5 bit offset via
  registerUserCategoryOffset() and add custom categories as
  subcategories of "all" so use/no warnings properly toggles them
- Warnings.enabled()/fatalEnabled(): no-arg form now uses caller's
  package name (not "all") matching Perl 5 behavior; check scope-based
  runtime suppression via $^WARNING_SCOPE
- Warnings.warnIf(): check scope-based runtime suppression before
  checking bits; walk stack past registered packages for custom categories
- Add findExternalCallerBits() helper implementing Perl 5's _error_loc()
  behavior: skip frames in warnings-registered packages to find external
  caller's warning bits
- Add getCallerPackageAtLevel() helper

This fixes "no warnings 'DateTime'" and similar custom category
suppression that was not working because:
1. Custom categories had no Perl5 bit offset assigned
2. Custom categories were not subcategories of "all"
3. warnif() checked immediate caller's bits instead of walking past
   the registered package to find the external caller

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@fglock fglock force-pushed the feature/lexical-warnings-phase1 branch from 401a057 to 533bc5c Compare March 30, 2026 09:26
@fglock @devin-ai-integration
Fix ASM frame error in constant-folded logical operators (VOID context)
fd1b700 
When a constant-folded && or || was emitted in VOID context (e.g.
print("a") if 0; print("b") if 0; which becomes 0 && print("a")),
the bytecode emitter was pushing a constant onto the stack and then
popping it. This corrupted ASM frame state at merge points, causing
NegativeArraySizeException in Frame.merge.

Fix: in VOID context, skip emission entirely for the short-circuit case
(constant result has no side effects), and for the non-short-circuit case
emit the RHS directly in VOID context without an extra pop.

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@fglock fglock changed the title WIP: Lexical warnings - Perl 5 parity Lexical warnings - Perl 5 parity Mar 30, 2026
@fglock @devin-ai-integration
Fix warning regressions: infnan.t, caller.t, readline.t
d465836 
Three fixes for regressions introduced in lexical-warnings-phase1:

1. WarnDie.warnWithCategory(): When warning bits exist but category
   is not lexically enabled, fall back to $^W flag instead of
   suppressing. Fixes 'isn not numeric' warnings not firing with -w.
   (op/infnan.t: +30 tests, now 1086 vs 1071 on master)

2. Per-call-site warning bits for caller()[9]: Add runtime tracking
   of warning bits at each statement (via WarningBitsRegistry
   callSiteBits/callerBitsStack). EmitCompilerFlag now emits
   setCallSiteBits() calls, and RuntimeCode.apply() saves/restores
   caller bits across subroutine boundaries. This gives caller()
   accurate per-statement warning bits instead of per-class bits.
   (op/caller.t: test 28 fixed)

3. CustomFileChannel.sysread(): Treat EISDIR as EOF without setting
   $! to avoid changing skip-guard behavior in readline tests.
   (op/readline.t: +2 tests, uni/readline.t: +2 tests)

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@fglock fglock merged commit 08a09ba into master Mar 30, 2026
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@fglock fglock deleted the feature/lexical-warnings-phase1 branch March 30, 2026 11:45
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