:error:build gcc6 cannot be built whilst libunwind-headers is installed.

[dbl001 (dbl)]

$ sudo port upgrade outdated
Password:
--->  Computing dependencies for isl
--->  Fetching archive for isl
--->  Attempting to fetch isl-0.21_0.darwin_15.x86_64.tbz2 from https://packages.macports.org/isl
--->  Attempting to fetch isl-0.21_0.darwin_15.x86_64.tbz2.rmd160 from https://packages.macports.org/isl
--->  Installing isl @0.21_0
--->  Cleaning isl
--->  Computing dependencies for isl
--->  Deactivating isl @0.20_0
--->  Cleaning isl
--->  Activating isl @0.21_0
--->  Cleaning isl
--->  Computing dependencies for cloog
--->  Fetching archive for cloog
--->  Attempting to fetch cloog-0.18.4_3.darwin_15.x86_64.tbz2 from https://packages.macports.org/cloog
--->  Attempting to fetch cloog-0.18.4_3.darwin_15.x86_64.tbz2.rmd160 from https://packages.macports.org/cloog
--->  Installing cloog @0.18.4_3
--->  Cleaning cloog
--->  Computing dependencies for cloog
--->  Deactivating cloog @0.18.4_2
--->  Cleaning cloog
--->  Activating cloog @0.18.4_3
--->  Cleaning cloog
--->  Computing dependencies for libgcc9
--->  Fetching archive for libgcc9
--->  Attempting to fetch libgcc9-9.1.0_1.darwin_15.x86_64.tbz2 from https://packages.macports.org/libgcc9
--->  Attempting to fetch libgcc9-9.1.0_1.darwin_15.x86_64.tbz2.rmd160 from https://packages.macports.org/libgcc9
--->  Installing libgcc9 @9.1.0_1
--->  Deactivating libgcc8 @8.3.0_0
--->  Activating libgcc9 @9.1.0_1
--->  Cleaning libgcc9
--->  Computing dependencies for libgcc8
--->  Fetching archive for libgcc8
--->  Attempting to fetch libgcc8-8.3.0_4.darwin_15.x86_64.tbz2 from https://packages.macports.org/libgcc8
--->  Attempting to fetch libgcc8-8.3.0_4.darwin_15.x86_64.tbz2.rmd160 from https://packages.macports.org/libgcc8
--->  Installing libgcc8 @8.3.0_4
--->  Cleaning libgcc8
--->  Computing dependencies for libgcc8
--->  Activating libgcc8 @8.3.0_4
--->  Cleaning libgcc8
--->  Computing dependencies for libgcc7
--->  Fetching archive for libgcc7
--->  Attempting to fetch libgcc7-7.4.0_3.darwin_15.x86_64.tbz2 from https://packages.macports.org/libgcc7
--->  Attempting to fetch libgcc7-7.4.0_3.darwin_15.x86_64.tbz2.rmd160 from https://packages.macports.org/libgcc7
--->  Installing libgcc7 @7.4.0_3
--->  Cleaning libgcc7
--->  Computing dependencies for libgcc7
--->  Deactivating libgcc7 @7.4.0_0
--->  Cleaning libgcc7
--->  Activating libgcc7 @7.4.0_3
--->  Cleaning libgcc7
--->  Computing dependencies for libgcc6
--->  Fetching archive for libgcc6
--->  Attempting to fetch libgcc6-6.5.0_4.darwin_15.x86_64.tbz2 from https://packages.macports.org/libgcc6
--->  Attempting to fetch libgcc6-6.5.0_4.darwin_15.x86_64.tbz2.rmd160 from https://packages.macports.org/libgcc6
--->  Installing libgcc6 @6.5.0_4
--->  Cleaning libgcc6
--->  Computing dependencies for libgcc6
--->  Deactivating libgcc6 @6.5.0_1
--->  Cleaning libgcc6
--->  Activating libgcc6 @6.5.0_4
--->  Cleaning libgcc6
--->  Computing dependencies for gcc6
--->  Fetching archive for gcc6
--->  Attempting to fetch gcc6-6.5.0_4.darwin_15.x86_64.tbz2 from https://packages.macports.org/gcc6
--->  Attempting to fetch gcc6-6.5.0_4.darwin_15.x86_64.tbz2 from http://sea.us.packages.macports.org/macports/packages/gcc6
--->  Attempting to fetch gcc6-6.5.0_4.darwin_15.x86_64.tbz2 from http://aus.us.packages.macports.org/macports/packages/gcc6
--->  Fetching distfiles for gcc6
--->  Verifying checksums for gcc6
--->  Extracting gcc6
--->  Applying patches to gcc6
--->  Configuring gcc6
--->  Building gcc6
Error: gcc6 cannot be built whilst libunwind-headers is installed.
Error: Failed to build gcc6: build error
Error: See /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc6/gcc6/main.log for details.
Error: Follow https://guide.macports.org/#project.tickets to report a bug.
MacBook-Pro:diagram davidlaxer$ vi /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc6/gcc6/main.log
MacBook-Pro:diagram davidlaxer$ cp !$ ~
cp /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc6/gcc6/main.log ~
MacBook-Pro:diagram davidlaxer$ 

[kencu (Ken)]

Yes, this is true. We need a different UI message that doesn't tell people to report this as a bug, though, and perhaps, like poppler, actually gives some instructions on what to do to fix the problem.

Sorry our instructions are not more clear.

[ryandesign (Ryan Carsten Schmidt)]

Please use PortGroup conflicts_build 1.0 and conflicts_build-append libunwind-headers instead; it prints instructions for what the user should do.

[ken-cunningham-webuse]

In 1b5363da60339b973851ce06ef8b83a796605d69/macports-ports (master):

gcc5-8: use conflicts_build libunwind-headers

instead of current more complicated/less clear blocker
closes: #58443