Fix #4739: Exempt combinations of Java fields and methods as double defs

compiler/src/dotty/tools/dotc/core/Contexts.scala

@@ -378,7 +378,6 @@ object Contexts {
      *   - as scope: The parameters of the auxiliary constructor.
      */
     def thisCallArgContext: Context = {
-      assert(owner.isClassConstructor)
       val constrCtx = outersIterator.dropWhile(_.outer.owner == owner).next()
       superOrThisCallContext(owner, constrCtx.scope)
         .setTyperState(typerState)

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

@@ -747,7 +747,8 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
    *  otherwise the current context.
    */
   def argCtx(app: untpd.Tree)(implicit ctx: Context): Context =
-    if (untpd.isSelfConstrCall(app)) ctx.thisCallArgContext else ctx
+    if (ctx.owner.isClassConstructor && untpd.isSelfConstrCall(app)) ctx.thisCallArgContext
+    else ctx
 
   /** Typecheck application. Result could be an `Apply` node,
    *  or, if application is an operator assignment, also an `Assign` or

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

@@ -744,7 +744,10 @@ trait Checking {
     def checkDecl(decl: Symbol): Unit = {
       for (other <- seen(decl.name)) {
         typr.println(i"conflict? $decl $other")
-        if (decl.matches(other)) {
+        def javaFieldMethodPair =
+          decl.is(JavaDefined) && other.is(JavaDefined) &&
+          decl.is(Method) != other.is(Method)
+        if (decl.matches(other) && !javaFieldMethodPair) {
           def doubleDefError(decl: Symbol, other: Symbol): Unit =
             if (!decl.info.isErroneous && !other.info.isErroneous)
               ctx.error(DoubleDeclaration(decl, other), decl.sourcePos)

tests/neg/i5004.scala

@@ -0,0 +1,6 @@
+object i0 {
+1 match {
+def this(): Int  // error // error
+  def this()     // error
+}                // error
+}

tests/pos/i4739.java

@@ -0,0 +1,6 @@
+public class i4739 {
+  int foo;
+  int foo() {
+    return this.foo;
+  }
+}