: _* is only valid when the parameter is repeated

Fixes scala#9749.
Fixes scala#9912.

Author: smarter

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

@@ -539,6 +539,8 @@ trait Applications extends Compatibility {
            *           in the remaining formal parameters.
            */
           def addTyped(arg: Arg, formal: Type): List[Type] =
+            if isVarArg(arg) && !formal.isRepeatedParam then
+              fail(i"Sequence argument type annotation `: _*` cannot be used here: the corresponding parameter has type $formal which is not a repeated parameter type", arg)
             addArg(typedArg(arg, formal), formal)
             if methodType.isParamDependent && typeOfArg(arg).exists then
               // `typeOfArg(arg)` could be missing because the evaluation of `arg` produced type errors

tests/neg-custom-args/fatal-warnings/i4008.scala

@@ -41,8 +41,10 @@ class ShouldntWarn4[Hello, World]
 
 
 @annotation.implicitNotFound("Hopefully you don't see this!")
-class C[A](using @annotation.implicitNotFound("No C[${B}] found") c: Class[A]) // error
+class C[A](implicit @annotation.implicitNotFound("No C[${B}] found") c: Class[A]) // error
 
-def someMethod1[A](using @annotation.implicitNotFound("No C[${B}] found") sc: C[A]) = 0 // error
+object Test {
+def someMethod1[A](implicit @annotation.implicitNotFound("No C[${B}] found") sc: C[A]) = 0 // error
 
-def someMethod2[A](using @annotation.implicitNotFound("No C[${A}] found") sc: C[A]) = ""
+def someMethod2[A](implicit @annotation.implicitNotFound("No C[${A}] found") sc: C[A]) = ""
+}

tests/neg/i9749.scala

@@ -0,0 +1,7 @@
+class A {
+  def f(x: Any) = 1
+
+  def foo(x: List[String]): Unit = {
+    f(x: _*) // error
+  }
+}

tests/pos-java-interop/i9912/JavaLogger.java

@@ -0,0 +1,5 @@
+public class JavaLogger {
+    public void info(String format, Object arg) {}
+
+    public void info(String in, Object... args){}
+}

tests/pos-java-interop/i9912/Test.scala

@@ -0,0 +1,9 @@
+class Test {
+  val logger = new JavaLogger
+  def log(): Unit = {
+      logger.info(
+        "My {} String {} with multiple args {}",
+        Array("a", "b", "c"): _*
+      )
+  }
+}

tests/pos/i9749.scala

@@ -0,0 +1,8 @@
+class A {
+  def f(x: Any) = 1
+  def f(x: String*) = 1
+
+  def foo(x: List[String]): Unit = {
+    f(x: _*)
+  }
+}