Name: rmT116609 Date: 12/08/2003


A DESCRIPTION OF THE REQUEST :
I just finished a project and had to spend a long time debugging a problem which turned out to be a very simple syntactical typo.
The problem I had was using "+=" for incrementing a variable. I accidentally typed "=+" which changed the operation into an assigment.



JUSTIFICATION :
I believe many people can be spared a headache if this specific typo would generate a compiler warning or error. It's very easy to overlook this when debugging code and it's use just doesn't make sense.
I can't think of a situation in which anyone would consciously use this syntax.
(Incident Review ID: 226951)
======================================================================
###@###.### 10/23/04 00:21 GMT
Contributed by java.net member dmytro_sheyko

A DESCRIPTION OF THE FIX :
  Bug number : 4965337
  Bug Description : Warn about =+
Diff Baseline : Mustang b67.
Comment : This fix warn not only about =+, but also about =-. In order to enable this warning we have to use -Xlint or -Xlint:assignunary command line options. Warning messages are not localized for 'ja' and 'zh_CN' locales.
Test Sample :
// tst/Main.java
public class Main {
public static void main(String[] args) {
int a = 0;
int b = 0;
a =- b; // warning
a =+ b; // warning
a=- b; // warning
a=+ b; // warning
a = - b; // ok, assignment and minus are separated
a = + b; // ok, assignment and plus are separated
a -= b; // ok, compound assignment
a += b; // ok, compound assignment
a =(-b); // ok, assignment and minus are separated
a =(+b); // ok, assignment and plus are separated
}
}
# test.cmd
echo enable warnings
javac -Xlint tst/Main.java
javac -Xlint:assignunary tst/Main.java
echo disable warnings
javac tst/Main.java
javac -Xlint:-assignunary tst/Main.java
Diff :
diff -u -r old\com\sun\tools\javac\code\Lint.java src\com\sun\tools\javac\code\Lint.java
--- old\com\sun\tools\javac\code\Lint.java Tue Jan 17 22:30:16 2006
+++ src\com\sun\tools\javac\code\Lint.java Sat Jan 21 22:35:46 2006
@@ -141,6 +141,11 @@
  EMPTY("empty"),
 
  /**
+ * Warn about unary minus or plus just after assignment operator.
+ */
+ ASSIGN_UNARY("assignunary"),
+
+ /**
  * Warn about falling through from one case of a switch statement to the next.
  */
  FALLTHROUGH("fallthrough"),
diff -u -r old\com\sun\tools\javac\comp\Attr.java src\com\sun\tools\javac\comp\Attr.java
--- old\com\sun\tools\javac\comp\Attr.java Tue Jan 17 22:30:16 2006
+++ src\com\sun\tools\javac\comp\Attr.java Sat Jan 21 21:32:56 2006
@@ -1474,6 +1474,7 @@
         Type owntype = attribTree(tree.lhs, env.dup(tree), VAR, Type.noType);
         Type capturedType = capture(owntype);
         attribExpr(tree.rhs, env, owntype);
+ chk.checkAssignUnary(tree);
         result = check(tree, capturedType, VAL, pkind, pt);
     }
 
diff -u -r old\com\sun\tools\javac\comp\Check.java src\com\sun\tools\javac\comp\Check.java
--- old\com\sun\tools\javac\comp\Check.java Tue Jan 17 22:30:16 2006
+++ src\com\sun\tools\javac\comp\Check.java Sat Jan 21 22:36:08 2006
@@ -1922,6 +1922,22 @@
  log.warning(tree.thenpart.pos(), "empty.if");
     }
 
+ /**
+ * Check for unary minus or plus just after simple assignment operator
+ */
+ void checkAssignUnary(JCAssign tree) {
+ if ((tree.pos + 1 == tree.rhs.pos) && lint.isEnabled(Lint.LintCategory.ASSIGN_UNARY)) {
+ switch(tree.rhs.tag) {
+ case JCTree.POS:
+ log.warning(tree.pos(), "assign.unary.plus");
+ break;
+ case JCTree.NEG:
+ log.warning(tree.pos(), "assign.unary.minus");
+ break;
+ }
+ }
+ }
+
     /** Check that symbol is unique in given scope.
      * @param pos Position for error reporting.
      * @param sym The symbol.
diff -u -r old\com\sun\tools\javac\main\Main.java src\com\sun\tools\javac\main\Main.java
--- old\com\sun\tools\javac\main\Main.java Tue Jan 17 22:30:16 2006
+++ src\com\sun\tools\javac\main\Main.java Sat Jan 21 22:14:39 2006
@@ -224,8 +224,8 @@
  new XOption("-Xlint", "opt.Xlint"),
  new XOption("-Xlint:{"
  + "all,"
- + "cast,deprecation,divzero,empty,unchecked,fallthrough,path,serial,finally,overrides,"
- + "-cast,-deprecation,-divzero,-empty,-unchecked,-fallthrough,-path,-serial,-finally,-overrides,"
+ + "cast,deprecation,divzero,empty,assignunary,unchecked,fallthrough,path,serial,finally,overrides,"
+ + "-cast,-deprecation,-divzero,-empty,-assignunary,-unchecked,-fallthrough,-path,-serial,-finally,-overrides,"
  + "none}",
  "opt.Xlint.suboptlist") {
  public boolean matches(String s) {
diff -u -r old\com\sun\tools\javac\resources\compiler.properties src\com\sun\tools\javac\resources\compiler.properties
--- old\com\sun\tools\javac\resources\compiler.properties Tue Jan 17 22:30:17 2006
+++ src\com\sun\tools\javac\resources\compiler.properties Sat Jan 21 22:13:48 2006
@@ -671,6 +671,12 @@
 compiler.warn.empty.if= [empty] empty statement after if
 
+compiler.warn.assign.unary.plus=+ [assignunary] probably simple assignment and unary plus (\=+) is used instead of compound assignment (+\=)
+
+compiler.warn.assign.unary.minus=+ [assignunary] probably simple assignment and unary minus (\=-) is used instead of compound assignment (-\=)
+
 #####
 
 ## The following are tokens which are non-terminals in the language. They should


FIX FOR BUG NUMBER:
4965337