Don't print system paths by default

mainly for compatibility with pkgconf. also the `--keep-system-libs`
flag seems to be used in practice [0] so seems to be worth it to support
it.

[0]: https://github.com/gentoo/gentoo/blob/b743fa0be223a9a220cae24820048d53b7ee0b31/dev-lang/python/python-3.10.9.ebuild#L234

README.md

@@ -27,7 +27,6 @@ summary:
 
 * Omits most `.pc` debugging features (`--print-…`)
 * No special handling of "uninstalled" packages, and no attendant knobs
-* No removal of standard system paths (e.g. `/usr/include`)
 * Skips checks unimplemented by pkg-config (i.e. `Conflicts:`)
 * Omits clunky redundant features (`--exists`, `--errors-to-stdout`, etc.)
 * Less strict `.pc` syntax

generic_main.c

@@ -18,6 +18,14 @@
 #  endif
 #endif
 
+#ifndef PKG_CONFIG_SYSTEM_INCLUDE_PATH
+#  define PKG_CONFIG_SYSTEM_INCLUDE_PATH "/usr/include"
+#endif
+
+#ifndef PKG_CONFIG_SYSTEM_LIBRARY_PATH
+#  define PKG_CONFIG_SYSTEM_LIBRARY_PATH "/lib" PATHDELIM "/usr/lib"
+#endif
+
 #ifndef PKG_CONFIG_PREFIX
 #  define PKG_CONFIG_PREFIX "/usr"
 #endif
@@ -85,6 +93,14 @@ int main(int argc, char **argv)
     if (!conf.fixedpath.s) {
         conf.fixedpath = S(pkg_config_path);
     }
+    conf.sys_incpath = fromcstr_(getenv("PKG_CONFIG_SYSTEM_INCLUDE_PATH"));
+    if (!conf.sys_incpath.s) {
+        conf.sys_incpath = S(PKG_CONFIG_SYSTEM_INCLUDE_PATH);
+    }
+    conf.sys_libpath = fromcstr_(getenv("PKG_CONFIG_SYSTEM_LIBRARY_PATH"));
+    if (!conf.sys_libpath.s) {
+        conf.sys_libpath = S(PKG_CONFIG_SYSTEM_LIBRARY_PATH);
+    }
     conf.top_builddir  = fromcstr_(getenv("PKG_CONFIG_TOP_BUILD_DIR"));
 
     appmain(conf);

u-config.c

@@ -51,6 +51,8 @@ typedef struct {
     Str envpath;      // $PKG_CONFIG_PATH or empty
     Str fixedpath;    // $PKG_CONFIG_LIBDIR or default
     Str top_builddir; // $PKG_CONFIG_TOP_BUILD_DIR or default
+    Str sys_incpath;  // $PKG_CONFIG_SYSTEM_INCLUDE_PATH or default
+    Str sys_libpath;  // $PKG_CONFIG_SYSTEM_LIBRARY_PATH or default
     Bool define_prefix;
     Byte delim;
 } Config;
@@ -805,6 +807,7 @@ static void usage(Out *out)
     "  --cflags, --cflags-only-I, --cflags-only-other\n"
     "  --define-prefix, --dont-define-prefix\n"
     "  --define-variable=NAME=VALUE, --variable=NAME\n"
+    "  --keep-system-cflags, --keep-system-libs\n"
     "  --libs, --libs-only-L, --libs-only-l, --libs-only-other\n"
     "  --modversion\n"
     "  --newlines\n"
@@ -1539,6 +1542,32 @@ static OutConfig newoutconf(Arena *a, Out *out, Out *err)
     return r;
 }
 
+static void insertsyspath(OutConfig *conf, Str path, Byte delim, Byte flag)
+{
+    Byte flagbuf[] = {'-', flag};
+    Str prefix = {flagbuf, SIZEOF(flagbuf)};
+    while (path.len) {
+        Arena snapshot = *conf->arena;
+        Cut c = cut(path, delim);
+        Str dir = c.head;
+        path = c.tail;
+        if (!dir.len) {
+            continue;
+        }
+        Str syspath = newstr(&snapshot, prefix.len+dir.len);
+        copy(copy(syspath, prefix), dir);
+        // NOTE(NRK): Technically, the path doesn't need to follow the flag
+        // immediately (e.g `-I /usr/include`). But I have not seen a single
+        // pc file that does this.
+        //
+        // In fact, `pkgconf` also fails to recognize `-I /usr/include` as
+        // a system include path! So this should be fine in practice.
+        if (insertstr(&snapshot, conf->seen, syspath)) {
+            *conf->arena = snapshot;
+        }
+    }
+}
+
 // Process the field while writing it to the output.
 static void fieldout(OutConfig *conf, Pkg *p, Str field)
 {
@@ -1589,6 +1618,8 @@ static void appmain(Config conf)
     Bool silent = 0;
     Bool static_ = 0;
     Bool modversion = 0;
+    Bool print_sysinc = 0;
+    Bool print_syslib = 0;
     Str variable = {0, 0};
 
     proc.define_prefix = conf.define_prefix;
@@ -1597,6 +1628,8 @@ static void appmain(Config conf)
     }
 
     *insert(a, &global, S("pc_path")) = conf.fixedpath;
+    *insert(a, &global, S("pc_system_includedirs")) = conf.sys_incpath;
+    *insert(a, &global, S("pc_system_libdirs")) = conf.sys_libpath;
     *insert(a, &global, S("pc_sysrootdir")) = S("/");
     *insert(a, &global, S("pc_top_builddir")) = conf.top_builddir;
 
@@ -1707,10 +1740,10 @@ static void appmain(Config conf)
             // Ignore
 
         } else if (equals(r.arg, S("-keep-system-cflags"))) {
-            // Ignore: already the default behavior
+            print_sysinc = 1;
 
         } else if (equals(r.arg, S("-keep-system-libs"))) {
-            // Ignore: already the default behavior
+            print_syslib = 1;
 
         } else if (equals(r.arg, S("-validate"))) {
             silent = 1;
@@ -1730,6 +1763,14 @@ static void appmain(Config conf)
         err = newnullout();
     }
 
+    if (!print_sysinc) {
+        insertsyspath(&outconf, conf.sys_incpath, conf.delim, 'I');
+    }
+
+    if (!print_syslib) {
+        insertsyspath(&outconf, conf.sys_libpath, conf.delim, 'L');
+    }
+
     for (Size i = 0; i < nargs; i++) {
         process(a, &proc, args[i]);
     }