Add jvm backend check for UTF-8 Constant length

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -142,7 +142,8 @@ class Compiler {
          new sjs.JUnitBootstrappers, // Generate JUnit-specific bootstrapper classes for Scala.js (not enabled by default)
          new CollectEntryPoints,     // Collect all entry points and save them in the context
          new CollectSuperCalls,      // Find classes that are called with super
-         new RepeatableAnnotations) :: // Aggregate repeatable annotations
+         new RepeatableAnnotations,  // Aggregate repeatable annotations
+         new CheckJVMSpecification) :: // Checks related to the JVM Specification before code generation
     Nil
 
   /** Generate the output of the compilation */

compiler/src/dotty/tools/dotc/transform/CheckJVMSpecification.scala

@@ -0,0 +1,43 @@
+package dotty.tools.dotc
+package transform
+
+import MegaPhase.MiniPhase
+import GenericSignatures.*
+import core.Contexts.*
+import core.Decorators.*
+import core.Constants.*
+import core.Symbols.*
+import util.SrcPos
+
+final class CheckJVMSpecification extends MiniPhase:
+  import ast.tpd.*
+
+  override def phaseName: String = CheckJVMSpecification.name
+  override def description: String = CheckJVMSpecification.description
+
+
+  override def transformDefDef(tree: DefDef)(using Context): Tree =
+    val sym = tree.symbol
+    val memberTpe = atPhase(ctx.base.erasurePhase) { sym.owner.denot.thisType.memberInfo(sym) }
+    for sig <- GenericSignatures.javaSig(sym, memberTpe) do
+      checkUTF8MaximumLength(sig, tree.srcPos, prefix = "Method signature")
+    tree
+
+  override def transformLiteral(tree: Literal)(using Context): Tree =
+    val Literal(cste) = tree
+    if cste.tpe == defn.StringType then
+      checkUTF8MaximumLength(cste.stringValue, tree.srcPos.focus, prefix = "String")
+    tree
+
+  /** See https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4.7 */
+  private def checkUTF8MaximumLength(str: String, pos: SrcPos, prefix: String)(using Context) =
+    val UTF8_MAX_LENGTH = 65535
+    if str.length > UTF8_MAX_LENGTH then
+      report.error(em"""${prefix} length exceed the maximum length allowed by the JVM specification.
+                        |Allowed: ${UTF8_MAX_LENGTH}
+                        |Actual : ${str.length}""", pos)
+
+object CheckJVMSpecification:
+  val name = "checkJVMspec"
+  val description = "check issues related to the jvm specification"
+

tests/neg/i15850-b.check

@@ -0,0 +1,6 @@
+-- Error: tests/neg/i15850-b.scala:9:4 ---------------------------------------------------------------------------------
+9 |def crash(x: Level7): Unit = () // error
+  |^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |Method signature length exceed the maximum length allowed by the JVM specification.
+  |Allowed: 65535
+  |Actual : 496979

tests/neg/i15850-b.scala

@@ -0,0 +1,9 @@
+type Level1 = Tuple4[Unit, Unit, Unit, Unit]
+type Level2 = Tuple4[Level1, Level1, Level1, Level1]
+type Level3 = Tuple4[Level2, Level2, Level2, Level2]
+type Level4 = Tuple4[Level3, Level3, Level3, Level3]
+type Level5 = Tuple4[Level4, Level4, Level4, Level4]
+type Level6 = Tuple4[Level5, Level5, Level5, Level5]
+type Level7 = Tuple4[Level6, Level6, Level6, Level6]
+
+def crash(x: Level7): Unit = () // error

tests/printing/transformed/lazy-vals-legacy.check

@@ -1,4 +1,4 @@
-[[syntax trees at end of MegaPhase{dropOuterAccessors, checkNoSuperThis, flatten, transformWildcards, moveStatic, expandPrivate, restoreScopes, selectStatic, Collect entry points, collectSuperCalls, repeatableAnnotations}]] // tests/printing/transformed/lazy-vals-legacy.scala
+[[syntax trees at end of MegaPhase{dropOuterAccessors, checkNoSuperThis, flatten, transformWildcards, moveStatic, expandPrivate, restoreScopes, selectStatic, Collect entry points, collectSuperCalls, repeatableAnnotations, checkJVMspec}]] // tests/printing/transformed/lazy-vals-legacy.scala
 package <empty> {
   @SourceFile("tests/printing/transformed/lazy-vals-legacy.scala") final module
     class A extends Object {

tests/printing/transformed/lazy-vals-new.check

@@ -1,4 +1,4 @@
-[[syntax trees at end of MegaPhase{dropOuterAccessors, checkNoSuperThis, flatten, transformWildcards, moveStatic, expandPrivate, restoreScopes, selectStatic, Collect entry points, collectSuperCalls, repeatableAnnotations}]] // tests/printing/transformed/lazy-vals-new.scala
+[[syntax trees at end of MegaPhase{dropOuterAccessors, checkNoSuperThis, flatten, transformWildcards, moveStatic, expandPrivate, restoreScopes, selectStatic, Collect entry points, collectSuperCalls, repeatableAnnotations, checkJVMspec}]] // tests/printing/transformed/lazy-vals-new.scala
 package <empty> {
   @SourceFile("tests/printing/transformed/lazy-vals-new.scala") final module
     class A extends Object {