Allow more control of redefined prefix behavior

Currently the native Win32 builds default to redefining the prefix
variable in .pc files based on their installation paths. This behavior
is not always desired when pkg-config is being used in a traditional
fixed path environment (e.g., /mingw like /usr).

Allow the default to be set via configure switch
--enable/disable-define-prefix, and allow it to be set both ways at
runtime through the --[dont-]define-prefix pkg-config option.

configure.ac

@@ -161,6 +161,19 @@ if test "$cross_compiling" = yes && test "$native_win32" = yes; then
    test "x$WINE" != x && TESTS_PKG_CONFIG='${WINE} '"$TESTS_PKG_CONFIG"
 fi
 
+dnl On Windows, the prefix variable in .pc files can be redfined at
+dnl runtime. Allow the default behavior to be controlled.
+AC_MSG_CHECKING([if prefix should be redefined at runtime])
+AC_ARG_ENABLE([define_prefix],
+  [AS_HELP_STRING([--enable-define-prefix],
+    [redefine prefix in .pc files @<:@default=yes on Win32@:>@])],
+  [],
+  [enable_define_prefix=$native_win32])
+AC_MSG_RESULT([$enable_define_prefix])
+AC_DEFINE_UNQUOTED([ENABLE_DEFINE_PREFIX],
+  [`test "x$enable_define_prefix" = xyes && echo TRUE || echo FALSE`],
+  [Define ${prefix} in .pc files at runtime])
+
 dnl
 dnl Find glib or use internal copy. Required version is 2.16 for
 dnl g_win32_get_package_installation_directory_of_module().

main.c

@@ -462,9 +462,13 @@ static const GOptionEntry options_table[] = {
     &output_opt_cb, "print which packages the package requires for static "
     "linking", NULL },
 #ifdef G_OS_WIN32
-  { "dont-define-prefix", 0, 0, G_OPTION_ARG_NONE, &dont_define_prefix,
-    "don't try to override the value of prefix for each .pc file found with "
-    "a guesstimated value based on the location of the .pc file", NULL },
+  { "define-prefix", 0, 0, G_OPTION_ARG_NONE, &define_prefix,
+    "try to override the value of prefix for each .pc file found with a "
+    "guesstimated value based on the location of the .pc file", NULL },
+  { "dont-define-prefix", 0, G_OPTION_FLAG_REVERSE, G_OPTION_ARG_NONE,
+    &define_prefix, "don't try to override the value of prefix for each .pc "
+    "file found with a guesstimated value based on the location of the .pc "
+    "file", NULL },
   { "prefix-variable", 0, 0, G_OPTION_ARG_STRING, &prefix_variable,
     "set the name of the variable that pkg-config automatically sets",
     "PREFIX" },

parse.c

@@ -35,7 +35,7 @@
 #include <sys/types.h>
 
 #ifdef G_OS_WIN32
-gboolean dont_define_prefix = FALSE;
+gboolean define_prefix = ENABLE_DEFINE_PREFIX;
 char *prefix_variable = "prefix";
 gboolean msvc_syntax = FALSE;
 #endif
@@ -968,7 +968,7 @@ parse_line (Package *pkg, const char *untrimmed, const char *path,
         pkg->vars = g_hash_table_new (g_str_hash, g_str_equal);
 
 #ifdef G_OS_WIN32
-      if (!dont_define_prefix && strcmp (tag, prefix_variable) == 0)
+      if (define_prefix && strcmp (tag, prefix_variable) == 0)
 	{
 	  /* This is the prefix variable. Try to guesstimate a value for it
 	   * for this package from the location of the .pc file.
@@ -1025,7 +1025,7 @@ parse_line (Package *pkg, const char *untrimmed, const char *path,
 	      goto cleanup;
 	    }
 	}
-      else if (!dont_define_prefix &&
+      else if (define_prefix &&
 	       orig_prefix != NULL &&
 	       strncmp (p, orig_prefix, strlen (orig_prefix)) == 0 &&
 	       G_IS_DIR_SEPARATOR (p[strlen (orig_prefix)]))

pkg-config.1

@@ -208,14 +208,23 @@ prints \fIfoo.lib\fP. Note that the --libs output consists of flags
 for the linker, and should be placed on the cl command line after a
 /link switch.
 .TP
+.I "--define-prefix"
+.TQ
 .I "--dont-define-prefix"
-This option is available only on Windows. It prevents \fIpkg-config\fP
-from automatically trying to override the value of the variable
-"prefix" in each .pc file.
+These options are available only on Windows. They control whether
+.I pkg-config
+overrides the value of the variable "prefix" in each .pc file. With
+\-\-define-prefix,
+.I pkg-config
+uses the installed location of the .pc file to determine the
+prefix. \-\-dont-define-prefix prevents this behavior. The default is
+usually \-\-define-prefix.
 .TP
 .I "--prefix-variable=PREFIX"
-Also this option is available only on Windows. It sets the name of the
-variable that \fIpkg-config\fP automatically sets as described above.
+This option is available only on Windows. It sets the name of the
+variable that
+.I pkg-config
+overrides instead of "prefix" when using the \-\-define-prefix feature.
 .TP
 .I "--static"
 Output libraries suitable for static linking.  That means including

pkg.h

@@ -134,9 +134,9 @@ extern char *pcsysrootdir;
 extern char *pkg_config_pc_path;
 
 #ifdef G_OS_WIN32
-/* If TRUE, do not automatically define "prefix"  while
- * parsing each .pc file */
-extern gboolean dont_define_prefix;
+/* If TRUE, define "prefix" in .pc files at runtime. */
+extern gboolean define_prefix;
+
 /* The name of the variable that acts as prefix, unless it is "prefix" */
 extern char *prefix_variable;