Skip caret when source is missing in initialization checker

compiler/src/dotty/tools/dotc/transform/init/Trace.scala

@@ -6,6 +6,7 @@ import core.*
 import Contexts.*
 import ast.tpd.*
 import util.SourcePosition
+import util.SourceFile
 
 import Decorators.*, printing.SyntaxHighlighting
 
@@ -42,17 +43,33 @@ object Trace:
 
   inline def extendTrace[T](node: Tree)(using t: Trace)(op: Trace ?=> T): T = op(using t.add(node))
 
+  /**
+   * Returns whether the source file exists
+   *
+   * The method SourceFile#exists always return true thus cannot be used.
+   */
+  def fileExists(source: SourceFile): Boolean =
+    source.content().nonEmpty
+
   def buildStacktrace(trace: Trace, preamble: String)(using Context): String = if trace.isEmpty then "" else preamble + {
     var lastLineNum = -1
     var lines: mutable.ArrayBuffer[String] = new mutable.ArrayBuffer
     trace.foreach { tree =>
       val isLastTraceItem = tree `eq` trace.last
       val pos = tree.sourcePos
+      val hasSource = fileExists(pos.source)
       val line =
-        if pos.source.exists then
-          val loc = "[ " + pos.source.file.name + ":" + (pos.line + 1) + " ]"
-          val code = SyntaxHighlighting.highlight(pos.lineContent.trim)
-          i"$code\t$loc"
+        if pos.exists then
+          // Show more information for external code without source
+          val file = if hasSource then pos.source.file.name else pos.source.file.path
+          val loc = file + ":" + (pos.line + 1)
+          val code =
+            if hasSource then
+              SyntaxHighlighting.highlight(pos.lineContent.trim)
+            else
+              "(no source)"
+
+          i"$code\t[ $loc ]"
         else
           tree match
             case defDef: DefTree =>
@@ -62,7 +79,7 @@ object Trace:
               tree.show.split(System.lineSeparator(), 2).head
 
       val positionMarkerLine =
-        if pos.exists && pos.source.exists then
+        if pos.exists && hasSource then
           (if isLastTraceItem then EMPTY_PADDING else CONNECTING_INDENT)+ positionMarker(pos)
         else
           ""

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -243,7 +243,7 @@ class CompilationTests {
     compileFilesInDir("tests/explicit-nulls/run", explicitNullsOptions)
   }.checkRuns()
 
-  // initialization tests
+  // initialization tests for global objects
   @Test def checkInitGlobal: Unit = {
     implicit val testGroup: TestGroup = TestGroup("checkInitGlobal")
     compileFilesInDir("tests/init-global/warn", defaultOptions.and("-Ysafe-init-global"), FileFilter.exclude(TestSources.negInitGlobalScala2LibraryTastyExcludelisted)).checkWarnings()
@@ -252,6 +252,20 @@ class CompilationTests {
       compileFilesInDir("tests/init-global/warn-tasty", defaultOptions.and("-Ysafe-init-global"), FileFilter.exclude(TestSources.negInitGlobalScala2LibraryTastyExcludelisted)).checkWarnings()
       compileFilesInDir("tests/init-global/pos-tasty", defaultOptions.and("-Ysafe-init-global", "-Werror"), FileFilter.exclude(TestSources.posInitGlobalScala2LibraryTastyExcludelisted)).checkCompile()
     end if
+
+    locally {
+      val group = TestGroup("checkInitGlobal/tastySource")
+      val tastSourceOptions = defaultOptions.and("-Ysafe-init-global")
+      val outDirLib = defaultOutputDir + group + "/A/tastySource/A"
+
+      // Set -sourceroot such that the source code cannot be found by the compiler
+      val libOptions = tastSourceOptions.and("-sourceroot", "tests/init-global/special")
+      val lib = compileFile("tests/init-global/special/tastySource/A.scala", libOptions)(group).keepOutput.checkCompile()
+
+      compileFile("tests/init-global/special/tastySource/B.scala", tastSourceOptions.withClasspath(outDirLib))(group).checkWarnings()
+
+      lib.delete()
+    }
   }
 
   // initialization tests

tests/init-global/special/tastySource/A.scala

@@ -0,0 +1,4 @@
+object A:
+  def foo(fn: => Int) = bar(fn)
+
+  def bar(fn: => Int) = fn

tests/init-global/special/tastySource/B.check

@@ -0,0 +1,13 @@
+-- Warning: tests/init-global/special/tastySource/B.scala:4:14 ---------------------------------------------------------
+4 |  def bar = C.n * 3      // warn
+  |            ^^^
+  |Reading mutable state of object C during initialization of object B.
+  |Reading mutable state of other static objects is forbidden as it breaks initialization-time irrelevance. Calling trace:
+  |├── object B:	[ B.scala:1 ]
+  |│   ^
+  |├── (no source)	[ tastySource/A.scala:2 ]
+  |├── (no source)	[ tastySource/A.scala:4 ]
+  |├── var y = A.foo(bar) * 2	[ B.scala:2 ]
+  |│                 ^^^
+  |└── def bar = C.n * 3      // warn	[ B.scala:4 ]
+  |              ^^^

tests/init-global/special/tastySource/B.scala

@@ -0,0 +1,7 @@
+object B:
+  var y = A.foo(bar) * 2
+
+  def bar = C.n * 3      // warn
+
+object C:
+  var n = 10