Backport "Warn if interpolator uses toString" to 3.3 LTS

compiler/src/dotty/tools/dotc/interactive/Completion.scala

@@ -172,12 +172,12 @@ object Completion:
         case _ => None
 
   private object StringContextApplication:
-    def unapply(path: List[tpd.Tree]): Option[tpd.Apply] = 
+    def unapply(path: List[tpd.Tree]): Option[tpd.Apply] =
       path match
-        case tpd.Select(qual @ tpd.Apply(tpd.Select(tpd.Select(_, StdNames.nme.StringContext), _), _), _) :: _ =>
+        case tpd.Select(qual @ tpd.Apply(tpd.Select(tpd.Select(_, nme.StringContext), _), _), _) :: _ =>
           Some(qual)
         case _ => None
-      
+
 
   /** Inspect `path` to determine the offset where the completion result should be inserted. */
   def completionOffset(untpdPath: List[untpd.Tree]): Int =
@@ -229,8 +229,8 @@ object Completion:
       // See example in dotty.tools.languageserver.CompletionTest.syntheticThis
       case tpd.Select(qual @ tpd.This(_), _) :: _ if qual.span.isSynthetic      => completer.scopeCompletions
       case StringContextApplication(qual) =>
-        completer.scopeCompletions ++ completer.selectionCompletions(qual) 
-      case tpd.Select(qual, _) :: _               if qual.typeOpt.hasSimpleKind => 
+        completer.scopeCompletions ++ completer.selectionCompletions(qual)
+      case tpd.Select(qual, _) :: _               if qual.typeOpt.hasSimpleKind =>
         completer.selectionCompletions(qual)
       case tpd.Select(qual, _) :: _                                             => Map.empty
       case (tree: tpd.ImportOrExport) :: _                                      => completer.directMemberCompletions(tree.expr)

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

@@ -222,6 +222,7 @@ enum ErrorMessageID(val isActive: Boolean = true) extends java.lang.Enum[ErrorMe
   case EnumMayNotBeValueClassesID // errorNumber: 206
   case IllegalUnrollPlacementID // errorNumber: 207  - unused in LTS
   case ExtensionHasDefaultID // errorNumber: 208
+  case FormatInterpolationErrorID // errorNumber: 209
 
   def errorNumber = ordinal - 1
 

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

@@ -23,6 +23,7 @@ enum MessageKind:
   case PotentialIssue
   case UnusedSymbol
   case Staging
+  case Interpolation
 
   /** Human readable message that will end up being shown to the user.
    *  NOTE: This is only used in the situation where you have multiple words

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

@@ -3208,3 +3208,8 @@ final class EnumMayNotBeValueClasses(sym: Symbol)(using Context) extends SyntaxM
 
     def explain(using Context) = ""
 end EnumMayNotBeValueClasses
+
+class BadFormatInterpolation(errorText: String)(using Context) extends Message(FormatInterpolationErrorID):
+  def kind = MessageKind.Interpolation
+  def msg(using Context) = errorText
+  def explain(using Context) = ""

compiler/src/dotty/tools/dotc/transform/localopt/FormatChecker.scala

@@ -12,6 +12,7 @@ import dotty.tools.dotc.core.Contexts.*
 import dotty.tools.dotc.core.Symbols.*
 import dotty.tools.dotc.core.Types.*
 import dotty.tools.dotc.core.Phases.typerPhase
+import dotty.tools.dotc.reporting.BadFormatInterpolation
 import dotty.tools.dotc.util.Spans.Span
 import dotty.tools.dotc.util.chaining.*
 
@@ -276,10 +277,16 @@ class TypedFormatChecker(partsElems: List[Tree], parts: List[String], args: List
     val pos = partsElems(index).sourcePos
     val bgn = pos.span.start + offset
     val fin = if end < 0 then pos.span.end else pos.span.start + end
-    pos.withSpan(Span(bgn, fin, bgn))
+    pos.withSpan(Span(start = bgn, end = fin, point = bgn))
 
   extension (r: report.type)
-    def argError(message: String, index: Int): Unit = r.error(message, args(index).srcPos).tap(_ => reported = true)
-    def partError(message: String, index: Int, offset: Int, end: Int = -1): Unit = r.error(message, partPosAt(index, offset, end)).tap(_ => reported = true)
-    def partWarning(message: String, index: Int, offset: Int, end: Int = -1): Unit = r.warning(message, partPosAt(index, offset, end)).tap(_ => reported = true)
+    def argError(message: String, index: Int): Unit =
+      r.error(BadFormatInterpolation(message), args(index).srcPos)
+        .tap(_ => reported = true)
+    def partError(message: String, index: Int, offset: Int, end: Int = -1): Unit =
+      r.error(BadFormatInterpolation(message), partPosAt(index, offset, end))
+        .tap(_ => reported = true)
+    def partWarning(message: String, index: Int, offset: Int, end: Int): Unit =
+      r.warning(BadFormatInterpolation(message), partPosAt(index, offset, end))
+        .tap(_ => reported = true)
 end TypedFormatChecker

tests/neg/f-interpolator-tests.check

@@ -1,8 +1,8 @@
--- Error: tests/neg/f-interpolator-tests.scala:4:19 --------------------------------------------------------------------
+-- [E209] Interpolation Error: tests/neg/f-interpolator-tests.scala:4:19 -----------------------------------------------
 4 |  def `um uh` = f"$s%d"  // error
   |                   ^
   |                   Found: (T.this.s : String), Required: Int, Long, Byte, Short, BigInt
--- Error: tests/neg/f-interpolator-tests.scala:10:10 -------------------------------------------------------------------
+-- [E209] Interpolation Error: tests/neg/f-interpolator-tests.scala:10:10 ----------------------------------------------
 10 |    f"x % y = ${x % y}%d" // error: illegal conversion character 'y'
    |          ^
    |          illegal conversion character 'y'

tests/neg/fEscapes.check

@@ -1,4 +1,4 @@
--- Error: tests/neg/fEscapes.scala:5:18 --------------------------------------------------------------------------------
+-- [E209] Interpolation Error: tests/neg/fEscapes.scala:5:18 -----------------------------------------------------------
 5 |  val fEscape = f"\u$octal%04x" // error
   |                  ^^
   |                  invalid unicode escape at index 1 of \u