Allow overriding package variables with env vars

pkg-config allows a way to override package variables through the
--define-prefix interface, but this is very cumbersome to do in a global
way since it always needs to be passed on the command line and the
override cannot be scoped to a single packge.

Allow overriding package variables using environment variables of the
form PKG_CONFIG_$PACKAGE_$VARIABLE. For example, setting
PKG_CONFIG_GLADEUI_2_0_CATALOGDIR will override the variable
"catalogdir" in the "gladeui-2.0" package.

https://bugs.freedesktop.org/show_bug.cgi?id=90917

4 files changed, 80 insertions, 2 deletions

diff --git a/check/Makefile.am b/check/Makefile.am
index 34d0e34..4f92e0d 100644
--- a/check/Makefile.am
+++ b/check/Makefile.am
@@ -26,7 +26,9 @@ TESTS = \
 	check-debug \
 	check-gtk \
 	check-tilde \
-	check-relocatable
+	check-relocatable \
+	check-variable-override \
+	$(NULL)
 
 EXTRA_DIST = \
 	$(TESTS) \
diff --git a/check/check-variable-override b/check/check-variable-override
new file mode 100755
index 0000000..e3f6cbd
--- /dev/null
+++ b/check/check-variable-override
@@ -0,0 +1,35 @@
+#! /bin/sh
+
+set -e
+
+. ${srcdir}/common
+
+# Check the normal behavior
+RESULT="/usr"
+run_test --variable=prefix simple
+RESULT="/usr/lib"
+run_test --variable=libdir simple
+
+# Override prefix with correct environment variable
+export PKG_CONFIG_SIMPLE_PREFIX="/foo"
+RESULT="/foo"
+run_test --variable=prefix simple
+RESULT="/foo/lib"
+run_test --variable=libdir simple
+RESULT="-I/foo/include"
+run_test --cflags simple
+unset PKG_CONFIG_SIMPLE_PREFIX
+
+# Override prefix with incorrect environment variable case. On Windows
+# this will have no effect as environment variables are case
+# insensitive.
+if [ "$native_win32" != yes ]; then
+    export PKG_CONFIG_SIMPLE_prefix="/foo"
+    RESULT="/usr"
+    run_test --variable=prefix simple
+    RESULT="/usr/lib"
+    run_test --variable=libdir simple
+    RESULT=""
+    run_test --cflags simple
+    unset PKG_CONFIG_SIMPLE_prefix
+fi
diff --git a/pkg-config.1 b/pkg-config.1
index 11e6292..f7daa81 100644
--- a/pkg-config.1
+++ b/pkg-config.1
@@ -338,6 +338,13 @@ Replaces the default
 .I pkg-config
 search directory, usually
 .IR /usr/lib/pkgconfig : /usr/share/pkgconfig .
+.TP
+.I "PKG_CONFIG_$PACKAGE_$VARIABLE"
+Overrides the variable VARIABLE in the package PACKAGE. The environment
+variable should have the package name and package variable upper cased
+with non-alphanumeric characters converted to underscores. For example,
+setting PKG_CONFIG_GLADEUI_2_0_CATALOGDIR will override the variable
+"catalogdir" in the "gladeui-2.0" package.
 .\"
 .SH PKG-CONFIG DERIVED VARIABLES
 .I pkg-config
diff --git a/pkg.c b/pkg.c
index c8bac4d..786ea4c 100644
--- a/pkg.c
+++ b/pkg.c
@@ -1021,6 +1021,24 @@ define_global_variable (const char *varname,
 }
 
 char *
+var_to_env_var (const char *pkg, const char *var)
+{
+  char *new = g_strconcat ("PKG_CONFIG_", pkg, "_", var, NULL);
+  char *p;
+  for (p = new; *p != 0; p++)
+    {
+      char c = g_ascii_toupper (*p);
+
+      if (!g_ascii_isalnum (c))
+        c = '_';
+
+      *p = c;
+    }
+
+  return new;
+}
+
+char *
 package_get_var (Package *pkg,
                  const char *var)
 {
@@ -1028,7 +1046,23 @@ package_get_var (Package *pkg,
 
   if (globals)
     varval = g_strdup (g_hash_table_lookup (globals, var));
-  
+
+  /* Allow overriding specific variables using an environment variable of the
+   * form PKG_CONFIG_$PACKAGENAME_$VARIABLE
+   */
+  if (pkg->key)
+    {
+      char *env_var = var_to_env_var (pkg->key, var);
+      const char *env_var_content = g_getenv (env_var);
+      g_free (env_var);
+      if (env_var_content)
+        {
+          debug_spew ("Overriding variable '%s' from environment\n", var);
+          return g_strdup (env_var_content);
+        }
+    }
+
+
   if (varval == NULL && pkg->vars)
     varval = g_strdup (g_hash_table_lookup (pkg->vars, var));