Count Unicode codepoints to compute columns

composer.json

@@ -20,6 +20,7 @@
     },
     "require": {
         "php": ">=8.1",
+        "ext-mbstring": "*",
         "league/uri": "^7.6",
         "league/uri-interfaces": "^7.6"
     },

src/SimpleSourceLocation.php

@@ -12,7 +12,7 @@ final class SimpleSourceLocation extends SourceLocationMixin
     /**
      * Creates a new location indicating $offset within $sourceUrl.
      *
-     * $line and $column default to assuming the source is a single line. This
+     * $line and $column default to assuming the source is a single ASCII line. This
      * means that $line defaults to 0 and $column defaults to $offset.
      */
     public function __construct(

src/SourceFile.php

@@ -212,12 +212,15 @@ private function binarySearch(int $offset): int
 
     /**
      * The 0-based column of that offset.
+     *
+     * Unlike offsets (which are byte-offsets), columns are computed based on Unicode
+     * codepoints to provide a better experience.
      */
     public function getColumn(int $offset): int
     {
         $line = $this->getLine($offset);
 
-        return $offset - $this->lineStarts[$line];
+        return mb_strlen(substr($this->string, $this->lineStarts[$line], $offset - $this->lineStarts[$line]), 'UTF-8');
     }
 
     /**
@@ -237,7 +240,17 @@ public function getOffset(int $line, int $column = 0): int
             throw new \OutOfRangeException('Column may not be negative.');
         }
 
-        $result = $this->lineStarts[$line] + $column;
+        if ($column === 0) {
+            $result = $this->lineStarts[$line];
+        } else {
+            $lineContent = substr($this->string, $this->lineStarts[$line], $this->lineStarts[$line + 1] ?? null);
+
+            if ($column > mb_strlen($lineContent, 'UTF-8')) {
+                throw new \OutOfRangeException("Line $line doesn't have $column columns.");
+            }
+
+            $result = $this->lineStarts[$line] + \strlen(mb_substr($lineContent, 0, $column, 'UTF-8'));
+        }
 
         if ($result > \strlen($this->string) || ($line + 1 < \count($this->lineStarts) && $result >= $this->lineStarts[$line + 1])) {
             throw new \OutOfRangeException("Line $line doesn't have $column columns.");

tests/SourceFileTest.php

@@ -254,4 +254,24 @@ public function testGetTextEndDefaultsToTheEndOfTheFile(): void
     {
         self::assertEquals("g boom\nzip zap zop", $this->file->getText(20));
     }
+
+    public function testGetColumnCountsUnicodeCharacters(): void
+    {
+        $file = SourceFile::fromString("foo\nbar éà\nbaz");
+
+        self::assertEquals(4, $file->getColumn(8));
+        self::assertEquals(5, $file->getColumn(10));
+        self::assertEquals(6, $file->getColumn(12));
+        self::assertEquals(0, $file->getColumn(13));
+    }
+
+    public function testGetOffsetCountsUnicodeCharactersForColumns(): void
+    {
+        $file = SourceFile::fromString("foo\nbar éà\nbaz");
+
+        self::assertEquals(8, $file->getOffset(1, 4));
+        self::assertEquals(10, $file->getOffset(1, 5));
+        self::assertEquals(12, $file->getOffset(1, 6));
+        self::assertEquals(13, $file->getOffset(2, 0));
+    }
 }