FULL PRODUCT VERSION :
java version "1.8.0_152"
Java(TM) SE Runtime Environment (build 1.8.0_152-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.152-b16, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
CYGWIN_NT-10.0 INFORMA-L7T6GPJ 2.9.0(0.318/5/3) 2017-09-12 10:18 x86_64 Cygwin

A DESCRIPTION OF THE PROBLEM :
A try-with-resource produces dead code. This results in inability to get to full-code-coverage (as reported by tools like jacoco).

The root of the problem is the strange "aconst_null"/"astore" that happens which is subseqently put through a "ifnull" checks. Many have noted it, such as this thread:
https://stackoverflow.com/questions/25615417/try-with-resources-introduce-unreachable-bytecode

try-with-resource has been broken since introduction (I think) in Java7. Full coverage has never been possible. Using older try-finally techniques (ala Java6) allows for full coverage.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
compile code and view in javap - output shown in 'expected result'

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
There should be no aconst_null (line 24) or astore 5 (line 25).

Having it causes the ifnull check (line 47) to be forced and lines 50-57 are unreachable, lines 60-69 unreachable (no exception possible from 50-57), and another forced outcome at line 100 making 103-110 unreachable, and 113-122 unreachable (no exception from 103-110 possible)
ACTUAL -
 public void dummy() throws java.sql.SQLException;
    Code:
       0: ldc #88 // String 1
       2: astore_1
       3: ldc #89 // String
       5: astore_2
       6: ldc #89 // String
       8: astore_3
       9: aload_0
      10: invokevirtual #90 // Method baz:()V
      13: ldc #88 // String 1
      15: ldc #89 // String
      17: ldc #89 // String
      19: invokestatic #91 // Method java/sql/DriverManager.getConnection:(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Ljava/sql/Connection;
      22: astore 4
      24: aconst_null
      25: astore 5
      27: aload_0
      28: invokevirtual #92 // Method foo:()V
      31: aload 4
      33: ifnull 40
      36: aload_0
      37: invokevirtual #93 // Method bar:()V
      40: aload 4
      42: ifnull 135
      45: aload 5
      47: ifnull 72
      50: aload 4
      52: invokeinterface #94, 1 // InterfaceMethod java/sql/Connection.close:()V
      57: goto 135
      60: astore 6
      62: aload 5
      64: aload 6
      66: invokevirtual #96 // Method java/lang/Throwable.addSuppressed:(Ljava/lang/Throwable;)V
      69: goto 135
      72: aload 4
      74: invokeinterface #94, 1 // InterfaceMethod java/sql/Connection.close:()V
      79: goto 135
      82: astore 6
      84: aload 6
      86: astore 5
      88: aload 6
      90: athrow
      91: astore 7
      93: aload 4
      95: ifnull 132
      98: aload 5
     100: ifnull 125
     103: aload 4
     105: invokeinterface #94, 1 // InterfaceMethod java/sql/Connection.close:()V
     110: goto 132
     113: astore 8
     115: aload 5
     117: aload 8
     119: invokevirtual #96 // Method java/lang/Throwable.addSuppressed:(Ljava/lang/Throwable;)V
     122: goto 132
     125: aload 4
     127: invokeinterface #94, 1 // InterfaceMethod java/sql/Connection.close:()V
     132: aload 7
     134: athrow
     135: aload_0
     136: invokevirtual #97 // Method bak:()V
     139: return
    Exception table:
       from to target type
          50 57 60 Class java/lang/Throwable
          27 40 82 Class java/lang/Throwable
          27 40 91 any
         103 110 113 Class java/lang/Throwable
          82 93 91 any


ERROR MESSAGES/STACK TRACES THAT OCCUR :
Code works OK, just produces dead code

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public void dummy() throws SQLException
{
final String dbUrl1 = "1";
final String username = "";
final String password = "";
baz();
        try (Connection conn1 = DriverManager.getConnection(dbUrl1,username,password)) {
         foo();
         if (conn1 != null)
         bar();
        }
        
bak();
}
public void foo() {/**/ }
public void bar() {/**/ }
public void baz() {/**/ }
public void bak() {/**/ }

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
switch back to try-finally for autocloseables.