validatePkgConfig: init

This adds the `validatePkgConfig` hook, which can be used to validate
pkg-config files in the output(s). Currently, this will just run
`pkg-config --validate` on all `.pc` files, capturing errors such as
the issue that was fixed in #87789.

The hook could be extended in the future with more fine-grained
checks.

doc/stdenv/stdenv.xml

@@ -2083,6 +2083,16 @@ postInstall = ''
       </para>
      </listitem>
     </varlistentry>
+    <varlistentry>
+     <term>
+      validatePkgConfig
+     </term>
+     <listitem>
+      <para>
+       The <literal>validatePkgConfig</literal> hook validates all pkg-config (<filename>.pc</filename>) files in a package. This helps catching some common errors in pkg-config files, such as undefined variables.
+      </para>
+     </listitem>
+    </varlistentry>
     <varlistentry>
      <term>
       cmake

pkgs/build-support/setup-hooks/validate-pkg-config.sh

@@ -0,0 +1,19 @@
+# This setup hook validates each pkgconfig file in each output.
+
+fixupOutputHooks+=(_validatePkgConfig)
+
+_validatePkgConfig() {
+    for pc in $(find "$prefix" -name '*.pc'); do
+        local bail=0
+
+        # Do not fail immediately. It's nice to see all errors when
+        # there are multiple pkgconfig files.
+        if ! pkg-config --validate "$pc"; then
+            bail=1
+        fi
+    done
+
+    if [ $bail -eq 1 ]; then
+        exit 1
+    fi
+}

pkgs/top-level/all-packages.nix

@@ -501,6 +501,10 @@ in
 
   iconConvTools = callPackage ../build-support/icon-conv-tools {};
 
+  validatePkgConfig = makeSetupHook
+    { name = "validate-pkg-config"; deps = [ findutils pkgconfig ]; }
+    ../build-support/setup-hooks/validate-pkg-config.sh;
+
   #package writers
   writers = callPackage ../build-support/writers {};