MDL-67151 core: format_float can auto detect number of decimal points

lib/moodlelib.php

@@ -8630,9 +8630,10 @@ function generate_password($maxlen=10) {
  * then it will display '5.4' instead of '5.400' or '5' instead of '5.000'.
  *
  * @param float $float The float to print
- * @param int $decimalpoints The number of decimal places to print.
+ * @param int $decimalpoints The number of decimal places to print. -1 is a special value for auto detect (full precision).
  * @param bool $localized use localized decimal separator
- * @param bool $stripzeros If true, removes final zeros after decimal point
+ * @param bool $stripzeros If true, removes final zeros after decimal point. It will be ignored and the trailing zeros after
+ *                         the decimal point are always striped if $decimalpoints is -1.
  * @return string locale float
  */
 function format_float($float, $decimalpoints=1, $localized=true, $stripzeros=false) {
@@ -8644,6 +8645,13 @@ function format_float($float, $decimalpoints=1, $localized=true, $stripzeros=fal
     } else {
         $separator = '.';
     }
+    if ($decimalpoints == -1) {
+        // The following counts the number of decimals.
+        // It is safe as both floatval() and round() functions have same behaviour when non-numeric values are provided.
+        $floatval = floatval($float);
+        for ($decimalpoints = 0; $floatval != round($float, $decimalpoints); $decimalpoints++);
+    }
+
     $result = number_format($float, $decimalpoints, $separator, '');
     if ($stripzeros) {
         // Remove zeros and final dot if not needed.

lib/tests/moodlelib_test.php

@@ -2249,6 +2249,14 @@ class core_moodlelib_testcase extends advanced_testcase {
         // Custom number of decimal places.
         $this->assertEquals('5.43000', format_float(5.43, 5));
 
+        // Auto detect the number of decimal places.
+        $this->assertEquals('5.43', format_float(5.43, -1));
+        $this->assertEquals('5.43', format_float(5.43000, -1));
+        $this->assertEquals('5', format_float(5, -1));
+        $this->assertEquals('5', format_float(5.0, -1));
+        $this->assertEquals('0.543', format_float('5.43e-1', -1));
+        $this->assertEquals('0.543', format_float('5.43000e-1', -1));
+
         // Option to strip ending zeros after rounding.
         $this->assertEquals('5.43', format_float(5.43, 5, true, true));
         $this->assertEquals('5', format_float(5.0001, 3, true, true));

lib/upgrade.txt

@@ -1,6 +1,9 @@
 This files describes API changes in core libraries and APIs,
 information provided here is intended especially for developers.
 
+=== 3.9 ===
+format_float() now accepts a special value (-1) as the $decimalpoints parameter which means auto-detecting number of decimal points.
+
 === 3.8 ===
 * The rotate_image function has been added to the stored_file class (MDL-63349)
 * The yui checknet module is removed. Call \core\session\manager::keepalive instead.