Fix #10681: Reject applied HK types in term positions

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

@@ -848,6 +848,17 @@ trait Applications extends Compatibility {
    *  Fallback if this fails: try to convert `E` to `new E`.
    */
   def typedFunPart(fn: untpd.Tree, pt: Type)(using Context): Tree =
+    /** typedFunPart should only adapt E to new E
+     *  when we're applying E to some term parameters: val x = String() works and
+     *  expands to val x = new String(), but val x = String doesn't, it should be
+     *  the same for the aliases of String.
+     */
+    def canTryNew(pt: Type)(using Context): Boolean =
+      pt match
+        case tp: FunProto => true
+        case tp: PolyProto => canTryNew(tp.resType)
+        case _ => false
+
     tryEither {
       typedExpr(fn, pt)
     } { (result, tstate) =>
@@ -856,7 +867,8 @@ trait Applications extends Compatibility {
         then nuState.commit() // nuState messages are more interesting that tstate's "not found"
         else tstate.commit()  // it's "not found" both ways; keep original message
         result
-      if untpd.isPath(fn) then tryNew(untpd)(fn, pt, fallBack)
+      if untpd.isPath(fn) && canTryNew(pt) then
+        tryNew(untpd)(fn, pt, fallBack)
       else fallBack(ctx.typerState)
     }
 

tests/neg/i10681.check

@@ -0,0 +1,97 @@
+-- [E006] Not Found Error: tests/neg/i10681.scala:2:15 ---------------------
+2 |val testGood = TestGood
+  |               ^^^^^^^^
+  |               Not found: TestGood
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:5:14 ---------------------
+5 |val testBad = TestBad[Nothing]
+  |              ^^^^^^^
+  |              Not found: TestBad
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:6:18 ---------------------
+6 |val testBadNoAp = TestBad
+  |                  ^^^^^^^
+  |                  Not found: TestBad
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:9:15 ---------------------
+9 |val testBad2 = TestBad2[Nothing]
+  |               ^^^^^^^^
+  |               Not found: TestBad2
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:10:19 --------------------
+10 |val testBad2NoAp = TestBad2
+   |                   ^^^^^^^^
+   |                   Not found: TestBad2
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:13:19 --------------------
+13 |val testBad3NoAp = TestBad3
+   |                   ^^^^^^^^
+   |                   Not found: TestBad3
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:14:24 --------------------
+14 |val testBad3PartialAp = TestBad3[String]
+   |                        ^^^^^^^^
+   |                        Not found: TestBad3
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:15:15 --------------------
+15 |val testBad3 = TestBad3[String][String]
+   |               ^^^^^^^^
+   |               Not found: TestBad3
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:18:18 --------------------
+18 |val testBad4Ap0 = TestBad4
+   |                  ^^^^^^^^
+   |                  Not found: TestBad4
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:19:18 --------------------
+19 |val testBad4Ap1 = TestBad4[Nothing]
+   |                  ^^^^^^^^
+   |                  Not found: TestBad4
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:20:18 --------------------
+20 |val testBad4Ap2 = TestBad4[Nothing, Nothing]
+   |                  ^^^^^^^^
+   |                  Not found: TestBad4
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:21:18 --------------------
+21 |val testBad4Ap3 = TestBad4[Nothing, Nothing][Nothing]
+   |                  ^^^^^^^^
+   |                  Not found: TestBad4
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:22:18 --------------------
+22 |val testBad4Ap4 = TestBad4[Nothing, Nothing][Nothing, Nothing]
+   |                  ^^^^^^^^
+   |                  Not found: TestBad4
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:23:18 --------------------
+23 |val testBad4Ap5 = TestBad4[Nothing, Nothing][Nothing, Nothing][Nothing]
+   |                  ^^^^^^^^
+   |                  Not found: TestBad4
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:27:12 --------------------
+27 |val test1 = PartialApplication[String]
+   |            ^^^^^^^^^^^^^^^^^^
+   |            Not found: PartialApplication
+
+longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i10681.scala:28:12 --------------------
+28 |val test2 = Curried[String][String]
+   |            ^^^^^^^
+   |            Not found: Curried
+
+longer explanation available when compiling with `-explain`
+16 errors found

tests/neg/i10681.scala

@@ -0,0 +1,28 @@
+type TestGood = String
+val testGood = TestGood // error
+
+type TestBad[A] = String
+val testBad = TestBad[Nothing] // error
+val testBadNoAp = TestBad // error
+
+type TestBad2 = [A] =>> String
+val testBad2 = TestBad2[Nothing] // error
+val testBad2NoAp = TestBad2 // error
+
+type TestBad3[A] = [B] =>> String
+val testBad3NoAp = TestBad3 // error
+val testBad3PartialAp = TestBad3[String] // error
+val testBad3 = TestBad3[String][String] // error
+
+type TestBad4[A, B] = [C, D] =>> [E] =>> String
+val testBad4Ap0 = TestBad4 // error
+val testBad4Ap1 = TestBad4[Nothing] // error
+val testBad4Ap2 = TestBad4[Nothing, Nothing] // error
+val testBad4Ap3 = TestBad4[Nothing, Nothing][Nothing] // error
+val testBad4Ap4 = TestBad4[Nothing, Nothing][Nothing, Nothing] // error
+val testBad4Ap5 = TestBad4[Nothing, Nothing][Nothing, Nothing][Nothing] // error
+
+type Curried = [X] =>> [Y] =>> String
+type PartialApplication[X] = Curried[String][X]
+val test1 = PartialApplication[String] // error
+val test2 = Curried[String][String] // error