[SV 10593] Export variables to $(shell ...) commands

Export all variables, including exported makefile variables, when
invoking a shell for the $(shell ...) function.  If we detect a
recursive variable expansion, silently ignore that variable and do
not export it.  We do print a debug message.

* NEWS: Announce the potential backward-incompatibility.
* doc/make.texi (Shell Function): Document the export behavior.
* src/main.c (main): Add "shell-export" to .FEATURES.
* src/job.h: New function to free struct childbase.
* src/job.c (free_childbase): Implement it; call from free_child.
* src/function.c (func_shell_base): Use target_environment() to
obtain the proper environment for the shell function.
Use free_childbase() to free memory.
(windows32_openpipe): Don't reset the environment: the caller
already provided a proper PATH variable in envp.
* src/variable.c (target_environment): If we detect a recursive
expansion and we're called from func_shell, ignore the variable.
(sync_Path_environment): Simplify and reduce memory allocation.
* tests/scripts/functions/shell: Add tests for this.

1 files changed, 51 insertions, 4 deletions

diff --git a/tests/scripts/functions/shell b/tests/scripts/functions/shell
index 63320a2b..80425172 100644
--- a/tests/scripts/functions/shell
+++ b/tests/scripts/functions/shell
@@ -32,14 +32,61 @@ foo: ; echo '$(FOO)'
 !,
               '', "echo '#'\n#\n");
 
-# Test shells inside exported environment variables.
-# This is the test that fails if we try to put make exported variables into
-# the environment for a $(shell ...) call.
+# Test that exported variables are passed to $(shell ...)
+$ENV{FOO} = 'baz';
+run_make_test(q!
+OUT = $(shell echo $$FOO)
+foo: ; @echo '$(OUT)'
+!,
+              '', 'baz');
+
+$ENV{FOO} = 'baz';
+run_make_test(q!
+FOO = bar
+OUT = $(shell echo $$FOO)
+foo: ; @echo '$(OUT)'
+!,
+              '', 'bar');
+
+run_make_test(q!
+export FOO = bar
+OUT = $(shell echo $$FOO)
+foo: ; @echo '$(OUT)'
+!,
+              '', 'bar');
+
+# Test shells inside exported environment variables, simply expanded.
+run_make_test('
+export HI := $(shell echo hi)
+.PHONY: all
+all: ; @echo $$HI
+',
+              '','hi');
+
+# Test shells inside exported environment variables.  See SV 10593
 run_make_test('
 export HI = $(shell echo hi)
 .PHONY: all
 all: ; @echo $$HI
-    ','','hi');
+',
+              '',"hi");
+
+$ENV{HI} = 'foo';
+run_make_test('
+HI = $(shell echo hi)
+.PHONY: all
+all: ; @echo $$HI
+',
+              '',"hi");
+
+$ENV{HI} = 'foo';
+run_make_test('
+HI = $(shell echo hi)
+bad := $(HI)
+.PHONY: all
+all: ; @echo $$HI $(bad)
+',
+              '',"hi hi");
 
 if ($port_type ne 'W32') {
     # Test shell errors in recipes including offset