Language: Compound assignment operators (.=, +=, -=, *=, etc.)

[PurHur]

Problem

PHPCfg parses Expr_AssignOp_* (e.g. $s .= $x, $n += 1), but lib/Compiler.php::compileExpr() has no lowering — lint reports Expr_AssignOp_ via #136 in UnsupportedRegistry.php.

Templates and counters use .= constantly; for loops (#192) often use += / ++ (#137).

Goal

All common compound assigns used in small web apps: at minimum .=, +=, -=, *=, /=, .=.

Implementation hints

Compiler (lib/Compiler.php)

• In compileExpr(), handle Op\Expr\AssignOp\Concat, Plus, Minus, etc. (grep AssignOp under vendor/ircmaxell/php-cfg for exact class names).
• Lower to read-modify-write: load target → apply binary op → store (may emit two TYPE_ASSIGN sequences before a dedicated opcode exists).

VM

• lib/Runtime.php already wires Optimizer\AssignOp — check if VM opcodes can delegate or mirror that resolver.
• lib/VM.php: ensure string .= uses string concat, numeric += uses numeric add (no silent cast surprises vs Zend).

JIT (lib/JIT.php)

• String .=: LLVM call to existing string concat builtin path (same as . binary op).
• Numeric compound ops: reuse arithmetic LLVM helpers from lib/JIT/Builtin/.

Tests

• test/compliance/cases/assignop_concat.phpt: $x = 'a'; $x .= 'b'; echo $x;
• test/compliance/cases/assignop_plus.phpt: $n = 1; $n += 2; echo $n;
• Register in capability matrix when JIT parity lands.

Acceptance criteria

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/vm.php -r '\$s = "Hello"; \$s .= " World"; echo \$s;'
docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/jit.php -r '\$s = "Hello"; \$s .= " World"; echo \$s;'

Both print Hello World. phpc lint clean for scripts using only supported assign ops.

Dependencies

• Pairs with Language: Null coalescing operator (??) in compiler pipeline #99 ??, Language: Ternary operator (?:) in compiler pipeline #114 ?:, Language: Double-quoted string interpolation ($var, {$obj->x}) #261 string interpolation (template building)
• Language: while, do-while, and for loops (CFG → VM → JIT) #192 / Language: Pre/post increment and decrement (++/--) #137 for loop increment patterns

Verification (local / Docker only)

./script/ci-local.sh --filter assignop — no GitHub Actions required.

Links

• lib/VM/Optimizer/AssignOp.php, lib/Lint/UnsupportedRegistry.php
• 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 ROADMAP Phase 2 (with Language: Null coalescing operator (??) in compiler pipeline #99, Language: Ternary operator (?:) in compiler pipeline #114)

[PurHur]

Implementation hints (backlog expansion)

Compiler

• php-cfg emits Expr_AssignOp_Concat, Expr_AssignOp_Plus, etc. — add cases in Compiler::compileExpr() before the Unsupported expression fallback.
• Pattern: evaluate LHS address → load current value → apply binary op → store (same as TYPE_ASSIGN + TYPE_CONCAT sequence).
• String .= must use string concat rules from existing TYPE_CONCAT / JIT\Helper string paths.

VM

• Reuse VM/Optimizer/AssignOp.php if present; otherwise emit two-step assign in lib/VM.php TYPE_ASSIGN handler.
• Verify ref parameters and properties are out of scope for v1 (document if unsupported).

JIT

• lib/JIT.php compileAssign path: in-place update for variables already in SSA/register form.
• Numeric += / -=: use existing JitValueCompare / binary op helpers.

Tests

test/compliance/cases/language/assignop_concat.phpt
test/compliance/cases/language/assignop_concat_jit.phpt

Local verify

./phpc lint -r '\$s="a"; \$s.="b"; echo \$s;'
./script/ci-local.sh --filter assignop

Dependencies

• Pairs with Language: Null coalescing operator (??) in compiler pipeline #99 for template defaults
• Language: while, do-while, and for loops (CFG → VM → JIT) #192 loops often use $i += 1 — can follow loops or land in parallel