Tweak message: make clear it is reassignment

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/init/Semantic.scala

@@ -1221,12 +1221,12 @@ object Semantic {
           eval(qual, thisV, klass)
           val res = eval(rhs, thisV, klass)
           extendTrace(rhs) {
-            res.ensureHot("The RHS of an assignment to a field must be fully initialized.")
+            res.ensureHot("The RHS of reassignment must be fully initialized.")
           }
         case id: Ident =>
           val res = eval(rhs, thisV, klass)
           extendTrace(rhs) {
-            res.ensureHot("The RHS of an assignment to a field must be fully initialized.")
+            res.ensureHot("The RHS of reassignment must be fully initialized.")
           }
 
       case closureDef(ddef) =>

tests/init/neg/inherit-non-hot.check

@@ -1,7 +1,7 @@
 -- Error: tests/init/neg/inherit-non-hot.scala:6:34 --------------------------------------------------------------------
 6 |            if b == null then b = new B(this) // error
   |                                  ^^^^^^^^^^^
-  |                                  The RHS of an assignment to a field must be fully initialized. Calling trace:
+  |                                  The RHS of reassignment must be fully initialized. Calling trace:
   |                                  -> object Foo {	[ inherit-non-hot.scala:2 ]
   |                                     ^
   |                                  -> val c = new C	[ inherit-non-hot.scala:19 ]

tests/init/neg/local-warm4.check

@@ -1,7 +1,7 @@
 -- Error: tests/init/neg/local-warm4.scala:18:20 -----------------------------------------------------------------------
 18 |                a = newA // error
    |                    ^^^^
-   |                    The RHS of an assignment to a field must be fully initialized. Calling trace:
+   |                    The RHS of reassignment must be fully initialized. Calling trace:
    |                    -> object localWarm {	[ local-warm4.scala:1 ]
    |                       ^
    |                    -> val a = new A(5)	[ local-warm4.scala:26 ]