[MacPorts] #73984: pango at 1.57.1: build fails with Apple clang 21 — comma-separated -Werror specifier rejected

[MacPorts]

#73984: pango at 1.57.1: build fails with Apple clang 21 — comma-separated -Werror
specifier rejected
--------------------+--------------------
 Reporter:  lukaso  |      Owner:  (none)
     Type:  defect  |     Status:  new
 Priority:  Normal  |  Milestone:
Component:  ports   |    Version:  2.12.5
 Keywords:          |       Port:  pango
--------------------+--------------------
 == Summary ==

 `x11/pango` 1.57.1 fails to configure / build on macOS with Apple clang 21
 (Xcode 26). The Portfile passes GCC-style comma-separated `-Werror`
 specifiers
 to the compiler:

 {{{
 -Wno-error,-Wimplicit-fallthrough
 -Wno-error,-Wmissing-declarations
 }}}

 Apple clang 21.0.0 (`clang-2100.0.123.102`) no longer accepts that comma
 form
 quietly: it now diagnoses

 {{{
 unknown -Werror warning specifier: '-Wno-error,-Wimplicit-fallthrough'
 [-Wunknown-warning-option]
 }}}

 Older Apple clang versions parsed the comma form as a single
 (unrecognised)
 token and silently moved on, so the same Portfile lines were harmless.
 With
 clang 21 the diagnostic is emitted and — because pango / meson promote
 `-Wunknown-warning-option` to an error during the per-flag feature probe —
 the
 configure step fails (or the build later fails when `werror` is in
 effect),
 even though the Portfile already appends `-Wno-error=unknown-warning-
 option`
 later in the same line.

 == Environment ==

  * macOS 26.3.1 (build 25D771280a), arm64
  * Xcode 26.4.1 (Build 17E202)
  * Apple clang version 21.0.0 (clang-2100.0.123.102)
  * MacPorts 2.12.5
  * Affected port: `x11/pango @1.57.1_0`

 == Steps to reproduce ==

 {{{
 sudo port -v install pango
 }}}

 == Minimal reproducer (no MacPorts needed) ==

 {{{
 $ echo 'int main(){return 0;}' | \
     clang -x c -Werror=unknown-warning-option \
                 -Wno-error,-Wimplicit-fallthrough - -o /tmp/t
 error: unknown -Werror warning specifier: '-Wno-error,-Wimplicit-
 fallthrough'
        [-Werror,-Wunknown-warning-option]
 1 error generated.
 }}}

 The equivalent equals form is accepted:

 {{{
 $ echo 'int main(){return 0;}' | \
     clang -x c -Werror=unknown-warning-option \
                 -Wno-error=implicit-fallthrough - -o /tmp/t
 $ echo $?
 0
 }}}

 == Offending Portfile lines ==

 `x11/pango/Portfile`, currently lines 55–61:

 {{{
 if { [string match *clang* ${configure.compiler}] } {
     configure.cflags-append \
                         -Wno-error,-Wimplicit-fallthrough \
                         -Wno-error,-Wmissing-declarations \
                         -Wno-error=unknown-warning-option \
                         -Wno-unknown-warning-option
 }
 }}}

 == Proposed fix ==

 Rewrite the two GCC-style comma flags to the equals form, which is the
 documented clang spelling and is also accepted by GCC (4.8+):

 {{{#!diff
 --- Portfile
 +++ Portfile
 @@
  if { [string match *clang* ${configure.compiler}] } {
      configure.cflags-append \
 -                        -Wno-error,-Wimplicit-fallthrough \
 -                        -Wno-error,-Wmissing-declarations \
 +                        -Wno-error=implicit-fallthrough \
 +                        -Wno-error=missing-declarations \
                          -Wno-error=unknown-warning-option \
                          -Wno-unknown-warning-option
  }
 }}}

 The block is already gated on `*clang*`, so this only changes behaviour
 for
 clang. The equals form has been the clang-documented spelling for a long
 time and is a no-op vs. the comma form on every Apple clang and upstream
 clang version that previously accepted the comma spelling — i.e. the
 change
 only stops emitting an unknown-warning diagnostic on clang 21+, while
 remaining benign on older clang.

-- 
Ticket URL: <https://trac.macports.org/ticket/73984>
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