Language: Ternary operator (?:) in compiler pipeline

[PurHur]

Problem

PHPCfg\Parser::parseExpr_Ternary() lowers ?: to CFG branches, but lib/Compiler.php has no handler for the resulting ops—any script using ternaries hits Unsupported expression.

Ternaries are ubiquitous in web apps (defaults, inline HTML flags, routing).

Goal

$x = $cond ? $a : $b compiles on VM, JIT, and AOT.

Implementation hints

1. Reproduce: bin/print.php -r '$x = $a ? $b : $c;' — note CFG block structure (JumpIf, assign blocks).
2. lib/Compiler.php: extend compileExpr() (or dedicated helper) for the ternary CFG op php-cfg emits after parseExpr_Ternary() — likely not a single Op\Expr\* node; trace with bin/print.php before guessing opcode names.
3. Lowering pattern: evaluate condition → TYPE_JUMPIF to true/false blocks → compile each arm → phi/assign merge to target variable (mirror compileSwitchStmt block linking).
4. lib/VM.php: both arms must produce compatible stack types; document mixed string/int behavior vs Zend.
5. lib/JIT.php: LLVM branch + Builder::phi at merge block for SSA values.
6. Lint: add registry entry until done (Lint: Register Phase-2 blockers in UnsupportedRegistry (ternary, .=, break) #258 pattern) if lint reports opaque errors.
7. Tests: test/compliance/cases/language/ternary.phpt (string, int, nested); optional test/compliance/cases/language/ternary_mixed.phpt.

Acceptance criteria

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/vm.php -r '$a=1; echo ($a>0)?"yes":"no";'
docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/jit.php -r '$a=1; echo ($a>0)?"yes":"no";'

Both print yes. phpc lint accepts compliant ternary scripts.

Verification (local / Docker only)

./script/ci-local.sh --filter ternary

Dependencies

• Compiler: VM/JIT comparison and equality for mixed types (routing guards) #90 mixed-type comparisons (ternary arms)
• Language: Null coalescing operator (??) in compiler pipeline #99 ?? (different opcode path — implement in parallel)
• Blocks ergonomic use in Web: MiniWebApp routing pattern (front controller + path dispatch) #210 / Reference: MiniWebApp lint-first skeleton (examples/003-MiniWebApp) #246 templates

Links

• lib/Compiler.php, lib/OpCode.php, lib/VM.php, lib/JIT.php
• 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 ROADMAP north-star Phase 1 (Language)

[PurHur]

Implementation hints (backlog architect — batch 8)

CFG / compiler entry points

1. Parse a minimal script with bin/print.php -r '\$x = true ? 1 : 2;' and inspect CFG — expect JumpIf + assign blocks (no dedicated ternary opcode today).
2. lib/Compiler.php::compileExpr() — add branch for coalesce/ternary CFG ops (grep Unsupported / default throws).
3. VM: branch merge may need a temporary slot; see how compileSwitchStmt wires TYPE_JUMPIF + block targets in compileStmt().

JIT

• lib/JIT.php — phi merge at join block when both arms produce values; mirror patterns from compileSwitchStmt lowering.
• Run one case: vendor/bin/phpunit --group llvm --filter JITTest after implementation.

Tests (add first)

• test/compliance/cases/language/ternary_simple.phpt — int arms
• test/compliance/cases/language/ternary_string.phpt — string concat in arms

Dependencies

• Language: while, do-while, and for loops (CFG → VM → JIT) #192 loops (orthogonal)
• Language: Null coalescing operator (??) in compiler pipeline #99 ?? — different AST node; implement separately
• Compiler: VM/JIT comparison and equality for mixed types (routing guards) #90 mixed comparisons in condition

Blocks

• examples/003-MiniWebApp inline defaults (Reference: MiniWebApp lint-first skeleton (examples/003-MiniWebApp) #246, Reference app: examples/003-MiniWebApp (router, templates, forms) #67)
• examples/001-SimpleWeb does not need ternary today

Verification

./phpc run -r 'echo (1 < 2) ? "yes" : "no";'
./script/ci-local.sh --filter ternary