Language: Double-quoted string interpolation ($var, {$obj->x})

[PurHur]

Problem

PHP web templates and APIs rely on double-quoted strings with embedded variables:

echo "Hello, $name";
echo "Route: {$route}";

If php-cfg emits Scalar_Encapsed / encapsed string parts that lib/Compiler.php does not lower, compilation fails with Unsupported expression or wrong output. Concatenation ('Hello ' . $name) works but is verbose and common in real apps (#67, templates in #246).

Goal

Support standard double-quoted interpolation in VM, JIT, and AOT for:

• Simple variables: "$name"
• Complex expressions in braces: "{$user['id']}", "{$obj->method()}" (v1 may limit to variables/array offsets)

Scope

• Audit php-cfg output for encapsed strings in PHPCfg\Operand
• Lower to string concat chain or dedicated opcode sequence in Compiler::compileExpr
• VM: evaluate parts left-to-right, concat
• JIT: LLVM concat of string values (reuse JitStringConcat / TYPE_CONCAT)
• PHPT: test/compliance/cases/language/encapsed_string.phpt
• Register in lib/Lint/UnsupportedRegistry.php until implemented (Lint: Register Phase-2 blockers in UnsupportedRegistry (ternary, .=, break) #258)

Acceptance criteria

$name = 'Dev';
echo "Hello, $name\n";

Identical output in bin/vm.php and bin/jit.php.

Verification (local only)

./script/ci-local.sh --filter encapsed
docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  ./script/ci-local.sh --filter encapsed

No GitHub Actions required.

Dependencies

• Language: Compound assignment operators (.=, +=, -=, *=, etc.) #136 compound .= (related string building)
• Language: Heredoc and nowdoc string literals #178 heredoc/nowdoc (separate lexer path)

Related

• Reference app: examples/003-MiniWebApp (router, templates, forms) #67 / Reference: MiniWebApp lint-first skeleton (examples/003-MiniWebApp) #246 MiniWebApp templates
• Docs: Rewrite README feature list to match current compiler (2026) #48 README capability list