fix(parser): classify auto-Decimal literals by real mantissa precision (#50) --skip-tests

The >=16-significant-digit float-literal-to-php::Decimal promotion
(docs/en/HIGH_PRECISION_TYPES.md) counted every digit in the raw
literal with preg_replace('/[^0-9]/'), so exponent digits and trailing
zeros counted as significant: 1.23456789012345e300 (15 significant
digits) and 999999999999999.0 became Decimal, making
is_float(2.220446049250313E-16) compile to false. Hex literals whose
digits contain E (0x123456789E1234567) matched the [.eE] test and
became Decimal("0x..."), where Zend folds an overflowing hex literal
to its exact double.

Three fixes, keeping the documented feature:
- Count true mantissa significant digits (strip sign, exponent,
  leading and trailing zeros) and additionally require that the double
  cannot reproduce the literal exactly - a literal that round-trips
  (every var_export/serialize output, PHP_FLOAT_EPSILON) has lost
  nothing and stays float, while 3.14159265358979323846 still promotes.
- Exclude hex/octal/binary notation from the reclassification.
- When a Decimal-classified literal meets a float-typed expression in
  a binary op or comparison, demote the literal to its exact double
  instead of the "Cannot convert float expression to Decimal" fatal:
  PHP evaluates every float literal as a double, so
  0.1 + 0.2 == 0.30000000000000004 is valid PHP and must be true.

phpunit/code/decimal-literal-classification.php

@@ -0,0 +1,31 @@
+<?php
+
+function fifteenSigDigitsWithExponent(): bool
+{
+    return is_float(1.23456789012345e300);
+}
+
+function trailingZerosAreNotSignificant(): bool
+{
+    return is_float(999999999999999.0);
+}
+
+function roundTripSixteenDigits(): bool
+{
+    return is_float(2.220446049250313E-16);
+}
+
+function hexLiteralStaysNumeric(): float
+{
+    return 0x123456789E1234567;
+}
+
+function autoDecimalKeepsPromotion()
+{
+    return 3.14159265358979323846;
+}
+
+function decimalLiteralDemotesAgainstFloat(float $f): bool
+{
+    return $f == 3.14159265358979323846;
+}

phpunit/src/DecimalLiteralClassificationTest.php

@@ -0,0 +1,58 @@
+<?php
+
+use TypePhp\CompilerTest;
+
+/**
+ * The auto-Decimal promotion applies to decimal literals whose mantissa has
+ * 16+ significant digits AND whose value the double cannot reproduce
+ * exactly. Exponent digits, leading zeros and trailing mantissa zeros carry
+ * no precision; hex/octal/binary literals fold to their exact numeric value
+ * like Zend; and a Decimal-classified literal meeting a float-typed
+ * expression demotes to its exact double instead of failing to compile.
+ */
+final class DecimalLiteralClassificationTest extends \BaseTest
+{
+    public function testOnlyGenuinePrecisionLossPromotesToDecimal(): void
+    {
+        $code = $this->compileFixture();
+
+        // Exactly one literal (the 21-digit pi) is promoted...
+        self::assertSame(1, substr_count($code, 'php::toDecimal('));
+        // ...and the borderline literals stay native floats, so every
+        // is_float() probe statically folds to true.
+        self::assertGreaterThanOrEqual(3, substr_count($code, 'php::toBool(true)'));
+    }
+
+    public function testHexLiteralFoldsToExactDouble(): void
+    {
+        $code = $this->compileFixture();
+
+        self::assertStringContainsString('2.0988295480315429e+19', $code);
+        self::assertStringNotContainsString('0x123456789E1234567', $code);
+    }
+
+    public function testDecimalLiteralDemotesAgainstFloatTypedExpression(): void
+    {
+        $code = $this->compileFixture();
+
+        // The comparison compiles (no "Cannot convert float expression to
+        // Decimal" fatal) and compares doubles like Zend.
+        self::assertStringContainsString('php::equals(f, 3.1415926535897931)', $code);
+    }
+
+    private function compileFixture(): string
+    {
+        global $translator;
+
+        $compiler = CompilerTest::create(TYPEPHP_ROOT_PATH);
+        $translator = $compiler;
+        $source = TYPEPHP_ROOT_PATH . '/phpunit/code/decimal-literal-classification.php';
+        $compiler->addFiles([$source]);
+        $compiler->prepareFile($source);
+        $generated = $compiler->convertFile($source);
+        $code = file_get_contents($generated);
+
+        self::assertIsString($code);
+        return $code;
+    }
+}

src/CompilerBase.php

@@ -160,6 +160,7 @@ class CompilerBase implements PropertyAccessContext
     protected const string ATTR_STATEMENT_EXPRESSION = 'aotStatementExpression';
     protected const string ATTR_MULTI_RETURN_IMPL = 'aotMultiReturnImpl';
     protected const string ATTR_SCOPED_CALLBACK = 'aotScopedCallback';
+    protected const string ATTR_FORCE_FLOAT_LITERAL = 'aotForceFloatLiteral';
 
     /**
      * Keyword methods (to* builtins) with mandated return types.

src/Parser/BinaryOpTrait.php

@@ -24,6 +24,8 @@ trait BinaryOpTrait
         $this->assertExprCanBeUsedAsValue($left, 'binary operand');
         $this->assertExprCanBeUsedAsValue($right, 'binary operand');
 
+        $this->demoteAutoDecimalLiteralAgainstFloat($left, $right);
+
         // Arithmetic logic: convert to a numeric type first when possible
         $leftExpr  = $this->parseOrderedBinaryOperand($left);
         $rightExpr = $this->parseOrderedBinaryOperand($right);
@@ -982,6 +984,7 @@ trait BinaryOpTrait
         if ($pythonOperator !== null) {
             return $pythonOperator;
         }
+        $this->demoteAutoDecimalLiteralAgainstFloat($expr->left, $expr->right);
         $left  = $this->parseCompareExpr($expr->left);
         $right = $this->parseCompareExpr($expr->right);
         $leftIsNative = $this->isNativeObjectClass($this->detectClassOfExpr($expr->left));
@@ -1144,8 +1147,36 @@ trait BinaryOpTrait
             ?? 'php::compare(' . $this->parseOrderedOperand($expr->left, false) . ', ' . $this->parseOrderedOperand($expr->right, false) . ')';
     }
 
+    /**
+     * When an auto-Decimal-classified float literal meets a float-typed
+     * expression in a binary operation, demote the literal to its exact
+     * double. PHP evaluates every float literal as a double, so rejecting
+     * the mix ("Cannot convert float expression to Decimal") refuses valid
+     * PHP — e.g. `0.1 + 0.2 == 0.30000000000000004` from a var_export round
+     * trip — and keeping the Decimal would change comparison semantics.
+     */
+    protected function demoteAutoDecimalLiteralAgainstFloat(NodeAbstract $left, NodeAbstract $right): void
+    {
+        if ($this->decimalTypes) {
+            return;
+        }
+        $leftType = $this->detectTypeOfExpr($left);
+        $rightType = $this->detectTypeOfExpr($right);
+        foreach ([[$left, $leftType, $rightType], [$right, $rightType, $leftType]] as [$node, $type, $otherType]) {
+            if ($type === Type::DECIMAL
+                && $otherType === Type::FLOAT
+                && $node instanceof Node\Scalar\Float_
+                && $this->isDecimalLiteral($node)
+            ) {
+                $node->setAttribute(self::ATTR_FORCE_FLOAT_LITERAL, true);
+            }
+        }
+    }
+
     protected function genBigNumericCmp(Expr\BinaryOp $expr, string $suffix = ''): ?string
     {
+        $this->demoteAutoDecimalLiteralAgainstFloat($expr->left, $expr->right);
+
         $leftType = $this->detectTypeOfExpr($expr->left);
         $rightType = $this->detectTypeOfExpr($expr->right);
 

src/Parser/TypeDetectionTrait.php

@@ -47,18 +47,103 @@ trait TypeDetectionTrait
 
     protected function isDecimalLiteral(Node\Scalar $expr): bool
     {
+        if ($expr->getAttribute(self::ATTR_FORCE_FLOAT_LITERAL, false)) {
+            return false;
+        }
         $rawValue = $expr->getAttribute('rawValue');
         if ($rawValue === null) {
             return false;
         }
         $clean = $this->stripNumericUnderscores($rawValue);
+        // Hex/octal/binary notation folds to its exact numeric value in Zend
+        // (an overflowing hex literal becomes the exact double); only decimal
+        // notation participates in the Decimal promotion. A hex literal whose
+        // digits contain E would otherwise match the exponent test below.
+        if (preg_match('/^[+-]?0[xXbBoO]/', $clean)) {
+            return false;
+        }
         // Must have a decimal point or exponent (not a pure integer)
         if (!preg_match('/[\.eE]/', $clean)) {
             return false;
         }
-        // Count significant digits (exclude ., e, E, +, -)
-        $digits = preg_replace('/[^0-9]/', '', $clean);
-        return strlen(ltrim($digits, '0')) >= 16;
+        // Documented rule: 16 or more significant digits promote to Decimal.
+        // Exponent digits carry no precision, and neither do leading or
+        // trailing mantissa zeros (999999999999999.0 has 15).
+        if ($this->countSignificantMantissaDigits($clean) < 16) {
+            return false;
+        }
+        // The promotion exists for literals that exceed double precision. A
+        // literal the double reproduces exactly — every var_export/serialize
+        // round-trip, PHP_FLOAT_EPSILON, ... — has lost nothing and stays a
+        // native float.
+        return !$this->floatLiteralRoundTripsExactly($clean);
+    }
+
+    /**
+     * Count the significant decimal digits of a numeric literal's mantissa:
+     * sign and exponent are ignored, leading zeros carry no precision, and
+     * trailing mantissa zeros do not require more precision than the double.
+     */
+    protected function countSignificantMantissaDigits(string $literal): int
+    {
+        $mantissa = ltrim($literal, '+-');
+        $mantissa = preg_split('/[eE]/', $mantissa)[0];
+        $digits = str_replace('.', '', $mantissa);
+        $digits = trim($digits, '0');
+        return strlen($digits);
+    }
+
+    /**
+     * Whether the decimal literal denotes exactly the value of its double
+     * representation (i.e. converting to double loses nothing).
+     */
+    protected function floatLiteralRoundTripsExactly(string $literal): bool
+    {
+        $value = (float) $literal;
+        if (!is_finite($value)) {
+            // The double overflowed; Decimal preserves the written value.
+            return false;
+        }
+        $shortest = $this->shortestFloatRepr($value);
+        return $this->normalizeDecimalLiteral($literal) === $this->normalizeDecimalLiteral($shortest);
+    }
+
+    /**
+     * Shortest decimal representation that parses back to exactly $value,
+     * independent of the precision/serialize_precision ini settings.
+     */
+    protected function shortestFloatRepr(float $value): string
+    {
+        for ($precision = 0; $precision <= 17; $precision++) {
+            $candidate = sprintf('%.' . $precision . 'e', $value);
+            if ((float) $candidate === $value) {
+                return $candidate;
+            }
+        }
+        return sprintf('%.17e', $value);
+    }
+
+    /**
+     * Normalize a decimal literal to [sign, significant digits, exponent] so
+     * two spellings of the same real number compare equal.
+     *
+     * @return array{string, string, int}|null
+     */
+    protected function normalizeDecimalLiteral(string $literal): ?array
+    {
+        if (!preg_match('/^([+-]?)(\d*)(?:\.(\d*))?(?:[eE]([+-]?\d+))?$/', trim($literal), $m)) {
+            return null;
+        }
+        $sign = $m[1] === '-' ? '-' : '+';
+        $fraction = $m[3] ?? '';
+        $exponent = (int) ($m[4] ?? 0) - strlen($fraction);
+        $digits = ltrim($m[2] . $fraction, '0');
+        $trimmed = rtrim($digits, '0');
+        $exponent += strlen($digits) - strlen($trimmed);
+        if ($trimmed === '') {
+            return ['+', '', 0];
+        }
+        return [$sign, $trimmed, $exponent];
     }
 
     protected function isFloatStr(string $str): bool

tests/compiler/float_edge/decimal-literal-classification.phpt

@@ -0,0 +1,32 @@
+--TEST--
+Auto-Decimal literal classification: significant digits, hex, float mixing
+--FILE--
+<?php
+declare(strict_types=1);
+
+function main(): void
+{
+    // 15 significant digits (exponent digits carry no precision): float.
+    var_dump(is_float(1.23456789012345e300));
+    // Trailing mantissa zeros carry no precision: float.
+    var_dump(is_float(999999999999999.0));
+    // 16 digits, but the double reproduces the value exactly: float.
+    var_dump(is_float(2.220446049250313E-16));
+    // Hex folds to its exact numeric value like Zend.
+    var_dump(0x123456789E1234567);
+    // var_export round-trip comparisons stay plain float comparisons.
+    var_dump(0.1 + 0.2 == 0.30000000000000004);
+    $f = 0.1;
+    var_dump($f + 0.2 == 0.30000000000000004);
+    // 21 significant digits still promote to Decimal (documented feature).
+    var_dump(is_float(3.14159265358979323846));
+}
+?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(true)
+float(2.098829548031543E+19)
+bool(true)
+bool(true)
+bool(false)