Add a Kconfig.env_vars attribute that lists env. variables

Kconfig.env_vars is a set() with the names of all environment variables
referenced in the configuration.

Can be used e.g. for custom incremental build implementations, though
sync_deps() already indirectly catches any relevant changes to
environment variables.

3 files changed, 45 insertions, 3 deletions

diff --git a/kconfiglib.py b/kconfiglib.py
index 5fdd9b7..38bdff2 100644
--- a/kconfiglib.py
+++ b/kconfiglib.py
@@ -479,6 +479,24 @@ class Kconfig(object):
       already indirectly catches any file modifications that change the
       configuration output.
 
+    env_vars:
+      A set() with the names of all environment variables referenced in the
+      Kconfig files.
+
+      Only environment variables referenced with the preprocessor $(FOO) syntax
+      will be registered. The older $FOO syntax is only supported for backwards
+      compatibility.
+
+      Also note that $(FOO) won't be registered unless the environment variable
+      $FOO is actually set. If it isn't, $(FOO) is an expansion of an unset
+      preprocessor variable (which gives the empty string).
+
+      Another gotcha is that environment variables referenced in the values of
+      recursively expanded preprocessor variables (those defined with =) will
+      only be registered if the variable is actually used (expanded) somewhere.
+
+      The note from the 'kconfig_filenames' documentation applies here too.
+
     n/m/y:
       The predefined constant symbols n/m/y. Also available in const_syms.
 
@@ -583,6 +601,7 @@ class Kconfig(object):
         "const_syms",
         "defconfig_list",
         "defined_syms",
+        "env_vars",
         "kconfig_filenames",
         "m",
         "mainmenu_text",
@@ -773,6 +792,7 @@ class Kconfig(object):
 
         # Not used internally. Provided as a convenience.
         self.kconfig_filenames = [filename]
+        self.env_vars = set()
 
         # These implement a single line of "unget" for the parser
         self._saved_line = None
@@ -2180,6 +2200,7 @@ class Kconfig(object):
 
         # Environment variables are tried last
         if fn in os.environ:
+            self.env_vars.add(fn)
             return os.environ[fn]
 
         return ""
diff --git a/tests/Kpreprocess b/tests/Kpreprocess
index 73053fe..2ebf6e6 100644
--- a/tests/Kpreprocess
+++ b/tests/Kpreprocess
@@ -69,7 +69,7 @@ qaz = QAZ
 echo = $(1)
 
 config PRINT_ME
-	string "$(ENV_VAR)" if ($(echo,FOO) && $(echo,BAR)) || !$(echo,BAZ) || !(($(qaz)))
+	string "$(ENV_1)" if ($(echo,FOO) && $(echo,BAR)) || !$(echo,BAZ) || !(($(qaz)))
 	default "$(echo,"foo")" if "foo $(echo,"bar") baz" = "$(undefined)"
 
 
@@ -128,3 +128,14 @@ error-n-res := $(error-if,n,oops)
 
 # Causes an error when expanded
 error-y-res = $(error-if,y,oops)
+
+
+# Environment variables (for testing Kconfig.env_vars). ENV_1 is already
+# referenced above.
+env_ref_1 := xxx $(ENV_2) xxx
+env_ref_2 := $(shell,echo $(ENV_3))
+env_ref_3 :=
+env_ref_3 += $(ENV_4)
+$(warning-if,$(ENV_5),$(ENV_UNDEFINED))
+source "$(ENV_6)"
+env_ref_4 = $(ENV_7)  # Never evaluated
diff --git a/testsuite.py b/testsuite.py
index 4faed1f..e22c775 100644
--- a/testsuite.py
+++ b/testsuite.py
@@ -2344,7 +2344,13 @@ config J
 
     print("Testing preprocessor")
 
-    os.environ["ENV_VAR"] = "env"
+    os.environ["ENV_1"] = "env_1"
+    os.environ["ENV_2"] = "env_2"
+    os.environ["ENV_3"] = "env_3"
+    os.environ["ENV_4"] = "env_4"
+    os.environ["ENV_5"] = "n"
+    os.environ["ENV_6"] = "Kconfiglib/tests/empty"
+    os.environ["ENV_7"] = "env_7"
     # We verify warnings manually
     c = Kconfig("Kconfiglib/tests/Kpreprocess", warn_to_stderr=False)
 
@@ -2392,7 +2398,7 @@ config J
     verify_str(c.syms["PRINT_ME"], r"""
 config PRINT_ME
 	string
-	prompt "env" if (FOO && BAR) || !BAZ || !QAZ
+	prompt "env_1" if (FOO && BAR) || !BAZ || !QAZ
 	default "\"foo\"" if "foo \"bar\" baz" = ""
 """)
 
@@ -2439,6 +2445,10 @@ config PRINT_ME
     else:
         fail("expanding error-y-res didn't raise an exception")
 
+    # Check Kconfig.env_vars
+    verify_equal(c.env_vars,
+                 set(("ENV_1", "ENV_2", "ENV_3", "ENV_4", "ENV_5", "ENV_6")))
+
     # Check that the expected warnings were generated
     verify_equal(c.warnings, [
         "Kconfiglib/tests/Kpreprocess:116: warning: 'echo message on stderr >&2' wrote to stderr: message on stderr",