Multi-span error reporting for consume and override errors

compiler/src/dotty/tools/dotc/cc/SepCheck.scala

@@ -461,10 +461,19 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
    */
   def consumeError(ref: Capability, loc: (SrcPos, TypeRole), pos: SrcPos)(using Context): Unit =
     val (locPos, role) = loc
-    report.error(
-      em"""Separation failure: Illegal access to $ref, which was ${role.howConsumed}
-          |on line ${locPos.line + 1} and therefore is no longer available.""",
-      pos)
+    val parts = List(
+      reporting.Diagnostic.DiagnosticPart(
+        "The capability was consumed here.",
+        locPos.sourcePos,
+        isPrimary = false
+      ),
+      reporting.Diagnostic.DiagnosticPart(
+        "Then, it was used here",
+        pos.sourcePos,
+        isPrimary = true
+      )
+    )
+    report.error(reporting.UseAfterConsume(ref, role.howConsumed), pos, parts)
 
   /** Report a failure where a capability is consumed in a loop.
    *  @param ref     the capability

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

@@ -72,6 +72,12 @@ object report:
     ctx.reporter.report(new Error(msg, fullPos))
     if ctx.settings.YdebugError.value then Thread.dumpStack()
 
+  /** Report an error with multi-span messages. */
+  def error(msg: Message, pos: SrcPos, parts: List[Diagnostic.DiagnosticPart])(using Context): Unit =
+    val fullPos = addInlineds(pos)
+    ctx.reporter.report(new Error(msg, fullPos, parts))
+    if ctx.settings.YdebugError.value then Thread.dumpStack()
+
   def error(msg: => String, pos: SrcPos)(using Context): Unit =
     error(msg.toMessage, pos)
 

compiler/src/dotty/tools/dotc/reporting/Diagnostic.scala

@@ -13,6 +13,13 @@ import core.Decorators.toMessage
 
 object Diagnostic:
 
+  /** A part of a multi-span diagnostic, associating text with a source position.
+   *  @param text       the message text for this part
+   *  @param srcPos     the source position where this part applies
+   *  @param isPrimary  whether this is the primary message (true) or a secondary note (false)
+   */
+  case class DiagnosticPart(text: String, srcPos: SourcePosition, isPrimary: Boolean)
+
   def shouldExplain(dia: Diagnostic)(using Context): Boolean =
     ctx.settings.explain.value && dia.msg.canExplain
     || ctx.settings.explainTypes.value && dia.msg.isInstanceOf[TypeMismatchMsg]
@@ -21,8 +28,9 @@ object Diagnostic:
   // `Diagnostics to be consumed by `Reporter` ---------------------- //
   class Error(
     msg: Message,
-    pos: SourcePosition
-  ) extends Diagnostic(msg, pos, ERROR):
+    pos: SourcePosition,
+    parts: List[DiagnosticPart] = Nil
+  ) extends Diagnostic(msg, pos, ERROR, parts):
     def this(str: => String, pos: SourcePosition) = this(str.toMessage, pos)
 
   /** A sticky error is an error that should not be hidden by backtracking and
@@ -31,8 +39,9 @@ object Diagnostic:
    */
   class StickyError(
     msg: Message,
-    pos: SourcePosition
-  ) extends Error(msg, pos)
+    pos: SourcePosition,
+    parts: List[DiagnosticPart] = Nil
+  ) extends Error(msg, pos, parts)
 
   /** A Warning with an origin. The semantics of `origin` depend on the warning.
    *  For example, an unused import warning has an origin that specifies the unused selector.
@@ -45,65 +54,72 @@ object Diagnostic:
 
   /** Lints are likely to be filtered. Provide extra axes for filtering by `-Wconf`.
    */
-  class LintWarning(msg: Message, pos: SourcePosition, origin: String = OriginWarning.NoOrigin)
-  extends Warning(msg, pos), OriginWarning(origin)
+  class LintWarning(msg: Message, pos: SourcePosition, origin: String = OriginWarning.NoOrigin, parts: List[DiagnosticPart] = Nil)
+  extends Warning(msg, pos, parts), OriginWarning(origin)
 
   class Warning(
     msg: Message,
-    pos: SourcePosition
-  ) extends Diagnostic(msg, pos, WARNING) {
-    def toError: Error = new Error(msg, pos).tap(e => if isVerbose then e.setVerbose())
-    def toInfo: Info = new Info(msg, pos).tap(e => if isVerbose then e.setVerbose())
+    pos: SourcePosition,
+    parts: List[DiagnosticPart] = Nil
+  ) extends Diagnostic(msg, pos, WARNING, parts) {
+    def toError: Error = new Error(msg, pos, parts).tap(e => if isVerbose then e.setVerbose())
+    def toInfo: Info = new Info(msg, pos, parts).tap(e => if isVerbose then e.setVerbose())
     def isSummarizedConditional(using Context): Boolean = false
   }
 
   class Info(
     msg: Message,
-    pos: SourcePosition
-  ) extends Diagnostic(msg, pos, INFO):
+    pos: SourcePosition,
+    parts: List[DiagnosticPart] = Nil
+  ) extends Diagnostic(msg, pos, INFO, parts):
     def this(str: => String, pos: SourcePosition) = this(str.toMessage, pos)
 
   abstract class ConditionalWarning(
     msg: Message,
-    pos: SourcePosition
-  ) extends Warning(msg, pos) {
+    pos: SourcePosition,
+    parts: List[DiagnosticPart] = Nil
+  ) extends Warning(msg, pos, parts) {
     def enablingOption(using Context): Setting[Boolean]
     override def isSummarizedConditional(using Context): Boolean = !enablingOption.value
   }
 
   class FeatureWarning(
     msg: Message,
-    pos: SourcePosition
-  ) extends ConditionalWarning(msg, pos) {
+    pos: SourcePosition,
+    parts: List[DiagnosticPart] = Nil
+  ) extends ConditionalWarning(msg, pos, parts) {
     def enablingOption(using Context): Setting[Boolean] = ctx.settings.feature
   }
 
   class UncheckedWarning(
     msg: Message,
-    pos: SourcePosition
-  ) extends ConditionalWarning(msg, pos) {
+    pos: SourcePosition,
+    parts: List[DiagnosticPart] = Nil
+  ) extends ConditionalWarning(msg, pos, parts) {
     def enablingOption(using Context): Setting[Boolean] = ctx.settings.unchecked
   }
 
-  class DeprecationWarning(msg: Message, pos: SourcePosition, origin: String)
-  extends ConditionalWarning(msg, pos), OriginWarning(origin):
+  class DeprecationWarning(msg: Message, pos: SourcePosition, origin: String, parts: List[DiagnosticPart] = Nil)
+  extends ConditionalWarning(msg, pos, parts), OriginWarning(origin):
     def enablingOption(using Context): Setting[Boolean] = ctx.settings.deprecation
 
-  class ConfigurationWarning(msg: Message, pos: SourcePosition) extends ConditionalWarning(msg, pos):
+  class ConfigurationWarning(msg: Message, pos: SourcePosition, parts: List[DiagnosticPart] = Nil) extends ConditionalWarning(msg, pos, parts):
     def enablingOption(using Context): Setting[Boolean] = ConfigurationWarning.setting
     override def isSummarizedConditional(using Context): Boolean = false
   object ConfigurationWarning:
     private val setting = Setting.internal("-configuration", value = true)
 
   class MigrationWarning(
     msg: Message,
-    pos: SourcePosition
-  ) extends Warning(msg, pos)
+    pos: SourcePosition,
+    parts: List[DiagnosticPart] = Nil
+  ) extends Warning(msg, pos, parts)
 
 class Diagnostic(
   val msg: Message,
   val pos: SourcePosition,
-  val level: Int
+  val level: Int,
+  val parts: List[Diagnostic.DiagnosticPart] = Nil
 ) extends interfaces.Diagnostic:
   private var verbose: Boolean = false
   def isVerbose: Boolean = verbose
@@ -117,6 +133,6 @@ class Diagnostic(
     msg.message.replaceAll("\u001B\\[[;\\d]*m", "")
   override def diagnosticRelatedInformation: JList[interfaces.DiagnosticRelatedInformation] =
     Collections.emptyList()
-
   override def toString: String = s"$getClass at $pos L${pos.line+1}: $message"
 end Diagnostic
+