Include span of bad args if multiline

[som-snytt]

Fixes #9434

The message position is tweaked only when the args are on a different line.

Then the source context includes the args; but only one caret for the point.

It would be nicer to request more context without changing the diagnostic position.

[warcholjakub]

What if tree.sourcePos is remapped (e.g. code has a magic header), while the union uses raw srcPos spans? Could that shift reported locations?

[som-snytt]

I'll look at how that is done. On Scala 2, the "underlying" position was a function of the source. Otherwise, how could one do any position calculation? However, I endorse my comment about using API to request more context instead of touching position.

[som-snytt]

Previously, shifting for funky headers was positionInUltimateSource, which may still be used in two places.

sourcePos.withSpan is the same as tree.source.atSpan or

val union = tree.sourcePos.copy(span = tree.srcPos.span.union(pt.args.last.srcPos.span))

Here we don't have a Positioned, we just want a SrcPos for reporting. Normally, reporting creates a Diagnostic and its SourcePosition together.

I won't push it further here, but it would be nice if reporting had a channel for extra pos info like inlined outers (currently a field in SourcePosition but really belongs to the diagnostic) and for this kludge a pos to say "rendering context should include this line".

[warcholjakub]

Makes sense. To be sure I tested it, and it doesn't seem to affect the case I mentioned.

[som-snytt]

I don't know what IDEs do with multiline squiggles, however. Also, one could not do this trick and also emit a rewrite suggestion.

[som-snytt]

Just a rebase and a random NPE. We ought not to normalize that.

[info] Test dotty.tools.dotc.ScalaJSCompilationTests.runScalaJS started
Test 'tests/run/i22888.scala' failed with output:                               
java.lang.NullPointerException: Cannot invoke "scala.concurrent.Future.onComplete(scala.Function1, scala.concurrent.ExecutionContext)" because "that" is null
	at scala.concurrent.impl.Promise$DefaultPromise.zipWith(Promise.scala:153)
	at scala.concurrent.Future$.traverse$$anonfun$1(Future.scala:884)
	at scala.collection.IterableOnceOps.foldLeft(IterableOnce.scala:740)
	at scala.collection.IterableOnceOps.foldLeft$(IterableOnce.scala:336)
	at scala.collection.AbstractIterator.foldLeft(Iterator.scala:1325)
	at scala.concurrent.Future$.traverse(Future.scala:884)
	at org.scalajs.linker.standard.StandardIRFileCache$CacheImpl.cached(StandardIRFileCache.scala:67)
	at dotty.tools.dotc.ScalaJSLink$.$anonfun$3(ScalaJSLink.scala:52)
	at scala.concurrent.impl.Promise$Transformation.run(Promise.scala:489)
	at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1395)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)

Error:  Test dotty.tools.dotc.ScalaJSCompilationTests.runScalaJS failed: java.lang.AssertionError: Run test failed, but should not, reasons:
Error:  encountered 1 test failure(s):
Error:    - generic failure (see test output), took 428.099 sec
Error:      at dotty.tools.vulpix.ParallelTesting$CompilationTest.checkPass(ParallelTesting.scala:1299)
Error:      at dotty.tools.vulpix.ParallelTesting$CompilationTest.checkRuns(ParallelTesting.scala:1259)
Error:      at dotty.tools.dotc.ScalaJSCompilationTests.runScalaJS(ScalaJSCompilationTests.scala:33)
Error:      at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
Error:      at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
Error:      at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
Error:      at java.lang.reflect.Method.invoke(Method.java:569)
Error:      ...
[info] Test dotty.tools.dotc.ScalaJSCompilationTests.negScalaJS started

================================================================================
Test Report
================================================================================

1 suites passed, 1 failed, 2 total
    tests/run/i22888.scala failed


[info] Test run dotty.tools.dotc.ScalaJSCompilationTests finished: 1 failed, 0 ignored, 2 total, 431.226s
Error:  Failed: Total 2, Failed 1, Errors 0, Passed 1
Error:  Failed tests:
Error:  	dotty.tools.dotc.ScalaJSCompilationTests
Error:  (sjsCompilerTests / Test / test) sbt.TestsFailedException: Tests unsuccessful
Error:  Total time: 818 s (0:13:38.0), completed Apr 10, 2026, 2:30:22 AM
Error: Process completed with exit code 1.

[warcholjakub]

LGTM

[mbovel]

This PR enhance error messages about extra parameters for multi-line method calls by also showing the extra arguments that are on separate lines in the error message.

For example, before we would show:

-- [E050] Type Error: tests/neg/19087.scala:13:22 ----------------------------------------------------------------------
13 |        foo(state.copy(x = 5): // Missing ")" // error: method copy in class State does not take more parameters
   |            ^^^^^^^^^^^^^^^^^
   |            method copy in class State does not take more parameters
   |

And after:

-- [E050] Type Error: tests/neg/19087.scala:13:22 ----------------------------------------------------------------------
13 |        foo(state.copy(x = 5): // Missing ")" // error: method copy in class State does not take more parameters
   |            ^
   |            method copy in class State does not take more parameters
   |
14 |          println("a")
   |

Note the new line 14 | println("a").

It looks good to me!