Fix Confusing source code position in error message

mdoc/src/main/scala/mdoc/internal/markdown/Renderer.scala

@@ -151,7 +151,7 @@ object Renderer {
                 case FailSection(instrumented, startLine, startColumn, endLine, endColumn) =>
                   val input = Input.String(instrumented)
                   val edit =
-                    TokenEditDistance.fromInputs(doc.sections.map(_.source.pos.input), input)
+                    TokenEditDistance.fromTrees(Seq(section.source.source), input)
                   val compiled = compiler.fail(edit, input, section.source.pos)
                   val tpos = new RangePosition(startLine, startColumn, endLine, endColumn)
                   val pos = tpos.toMeta(section)

tests/unit/src/test/scala-3/tests/markdown/FailPositionSuite.scala

@@ -0,0 +1,43 @@
+package tests.markdown
+
+import tests.markdown.StringSyntax._
+import tests.markdown.Compat
+
+class FailPositionSuite extends BaseMarkdownSuite {
+
+  check(
+    "position",
+    """|```scala mdoc
+       |extension (x: Int)
+       |    def ===(y: Int) = x == y
+       |```
+       |
+       |```scala mdoc:fail
+       |1 === ""
+       |```
+       |
+       |```scala mdoc:silent
+       | 1 === 1    
+       |```
+    """.stripMargin,
+    """|```scala
+       |extension (x: Int)
+       |    def ===(y: Int) = x == y
+       |```
+       |
+       |```scala
+       |1 === ""
+       |// error:
+       |// Found:    ("" : String)
+       |// Required: Int
+       |// 1 === ""
+       |//       ^^
+       |```
+       |
+       |```scala
+       | 1 === 1    
+       |```
+    """.stripMargin
+  )
+
+}

tests/unit/src/test/scala/tests/markdown/FailSuite.scala

@@ -381,46 +381,48 @@ class FailSuite extends BaseMarkdownSuite {
     "two-errors",
     """
       |```scala mdoc:fail
-      |val nope = "foo" * "goo"
+      |val one = "foo" * "goo"
       |```
       |
       |```scala mdoc:fail
-      |val bad = "moo" * "loo"
+      |val two = "moo" * "loo"
       |```
     """.stripMargin,
     """|```scala
-       |val nope = "foo" * "goo"
+       |val one = "foo" * "goo"
        |// error: type mismatch;
        |//  found   : String("goo")
        |//  required: Int
+       |// val one = "foo" * "goo"
+       |//                   ^^^^^
        |```
        |
        |```scala
-       |val bad = "moo" * "loo"
+       |val two = "moo" * "loo"
        |// error: type mismatch;
        |//  found   : String("loo")
        |//  required: Int
-       |// val bad = "moo" * "loo"
+       |// val two = "moo" * "loo"
        |//                   ^^^^^
        |```
        |""".stripMargin,
     compat = Map(
       Compat.Scala3 ->
         """|```scala
-           |val nope = "foo" * "goo"
+           |val one = "foo" * "goo"
            |// error:
            |// Found:    ("goo" : String)
            |// Required: Int
-           |// val nope = "foo" * "goo"
-           |//                    ^^^^^
+           |// val one = "foo" * "goo"
+           |//                   ^^^^^
            |```
            |
            |```scala
-           |val bad = "moo" * "loo"
+           |val two = "moo" * "loo"
            |// error:
            |// Found:    ("loo" : String)
            |// Required: Int
-           |// val bad = "moo" * "loo"
+           |// val two = "moo" * "loo"
            |//                   ^^^^^
            |```
            |""".stripMargin