-Wmisleading-indentation in OpenJDK

Inspired by this post by Mark Wielaard I started wondering how OpenJDK 9 would fare in a -Wmisleading-indentation test. So I built OpenJDK 9 using -Wall to find out.

First, though, a big heads up: the OpenJDK 9 build selectively enables and disables warnings and turns on -Werorr. There doesn’t seem to be a straight- forward way of enabling all compiler warnings everywhere. I ended up patching various makefiles to comment out various DISABLED_WARNINGS* flags. Hotspot needed a separate patch to initialize WARNING_FLAGS with -Wall in hotspot/make/linux/makefiles/gcc.make. Then I built OpenJDK 9 using:

mkdir build
cd build
bash ../configure --with-extra-cflags="-Wall -Wextra" --with-extra-cxxflags="-Wall -Wextra -fpermissive" --disable-warnings-as-errors

A grep misleading-indentation build.log was surprising:

jdk9-dev/jdk/src/java.base/share/native/libfdlibm/e_asin.c:103:17: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.base/share/native/libfdlibm/k_rem_pio2.c:201:61: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmscgats.c:613:13: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmscgats.c:690:13: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmsintrp.c:959:29: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmsintrp.c:1023:29: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmsio1.c:717:9: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmsopt.c:557:13: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmsopt.c:1021:29: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmsps2.c:1015:9: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmstypes.c:2398:9: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmstypes.c:2679:9: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/liblcms/cmswtpnt.c:109:9: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/libfontmanager/layout/SunLayoutEngine.cpp:154:25: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/libsplashscreen/libpng/pngread.c:3880:16: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
jdk9-dev/jdk/src/java.desktop/share/native/libsplashscreen/libpng/pngread.c:3997:10: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]

libfdlibm, liblcms and libpng are all external libraries that are bundled with OpenJDK. In the case of Linux distributions, they are often replaced with dynamically linked system libraries. That only code that’s actually part of OpenJDK itself is libfontmanager.

Let’s take a look at that. The warning itself is:

/home/omajid/jdk9-dev/jdk/src/java.desktop/share/native/libfontmanager/layout/SunLayoutEngine.cpp:154:25: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
   if (min < 0) min = 0; if (max < min) max = min; /* defensive coding */
                         ^~
/home/omajid/jdk9-dev/jdk/src/java.desktop/share/native/libfontmanager/layout/SunLayoutEngine.cpp:154:3: note: ...this 'if' clause, but it is not
   if (min < 0) min = 0; if (max < min) max = min; /* defensive coding */
   ^~

So gcc thinks the programmer meant to guard the second if statement with the first but failed to do so. But a quick look at the code suggests that these are indeed two independent checks - one checks and fixes min and the other fixes max. The developer just tried to save whitespace and write them in one line. Definitely a false postive.

Anyway, I am impressed with OpenJDK’s code quality: gcc doesn’t find any actual misleading indentation issues in OpenJDK.