Only refine type of inline vals marked as transparent

Author: nicolasstucki

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -887,17 +887,20 @@ trait Checking {
    */
   def checkInlineConformant(tpt: Tree, tree: Tree, sym: Symbol)(using Context): Tree = {
     if sym.is(Inline, butNot = DeferredOrTermParamOrAccessor) && !ctx.erasedTypes && !ctx.inInlineMethod then
-      tree.tpe.widenTermRefExpr.dealias match
-        case tp: ConstantType =>
-          // final vals can be marked inline even if they're not pure, see Typer#patchFinalVals
-          val purityLevel = if (sym.is(Final)) Idempotent else Pure
-          if !(exprPurity(tree) >= purityLevel) then
-            ctx.error("inline value must be pure", tree.sourcePos)
-          if tree.tpe =:= tpt.tpe then tpt
-          else TypeTree(tree.tpe).withSpan(tpt.span)
+      // final vals can be marked inline even if they're not pure, see Typer#patchFinalVals
+      val purityLevel = if (sym.is(Final)) Idempotent else Pure
+      if !(exprPurity(tree) >= purityLevel) then
+        ctx.error("inline value must be pure", tree.sourcePos)
+        tpt
+      else tpt.tpe.widenTermRefExpr.dealias match
+        case tp: ConstantType => tpt
         case _ =>
-          ctx.error("inline value must have a literal constant type", tree.sourcePos)
-          tpt
+          if sym.is(Transparent)  then
+            TypeTree(tree.tpe).withSpan(tpt.span)
+          else
+            val pos = if tpt.span.isZeroExtent then tree.sourcePos else tpt.sourcePos
+            ctx.error("inline value must have a literal constant type", pos)
+            tpt
     else
       tpt
   }

tests/neg/i8841.check

@@ -1,3 +1,7 @@
+-- Error: tests/neg/i8841.scala:2:20 -----------------------------------------------------------------------------------
+2 |  inline val log1 : Boolean = false // error
+  |                    ^^^^^^^
+  |                    inline value must have a literal constant type
 -- Error: tests/neg/i8841.scala:3:20 -----------------------------------------------------------------------------------
 3 |  inline val log2 = true: Boolean // error
   |                    ^^^^^^^^^^^^^

tests/neg/i8841.scala

@@ -1,5 +1,5 @@
 object Foo {
-  inline val log1 : Boolean = false
+  inline val log1 : Boolean = false // error
   inline val log2 = true: Boolean // error
   inline val log3: false  = { println(); false } // error
 }

tests/neg/inline-val.scala

@@ -1,4 +1,4 @@
 
 inline val a = 1 : Int // error
-inline val b: Int = 1
+inline val b: Int = 1 // error
 inline val c = b // error

tests/pos/inline-vals.scala

@@ -23,13 +23,13 @@ object Constants extends InlineConstants {
 }
 
 class Constants2 {
-  inline val myInlinedBoolean: Boolean = true
-  inline val myInlinedByte: Byte = 1
-  inline val myInlinedShort: Short = 2
-  inline val myInlinedInt: Int = 3
-  inline val myInlinedLong: Long = 4
-  inline val myInlinedFloat: Float = 5
-  inline val myInlinedDouble: Double = 6
-  inline val myInlinedChar: Char = 'a'
-  inline val myInlinedString: String = "abc"
-}
+  transparent inline val myInlinedBoolean: Boolean = true
+  transparent inline val myInlinedByte: Byte = 1
+  transparent inline val myInlinedShort: Short = 2
+  transparent inline val myInlinedInt: Int = 3
+  transparent inline val myInlinedLong: Long = 4
+  transparent inline val myInlinedFloat: Float = 5
+  transparent inline val myInlinedDouble: Double = 6
+  transparent inline val myInlinedChar: Char = 'a'
+  transparent inline val myInlinedString: String = "abc"
+}