make: add support for CURDIR macro

Austin Group defect report 1626 introduced support for the CURDIR
macro:

   https://www.austingroupbugs.net/view.php?id=1626

Implement this as a POSIX 202X feature.

Adds 160-176 bytes.

2 files changed, 53 insertions, 5 deletions

diff --git a/miscutils/make.c b/miscutils/make.c
index fca00d8e3..f594e196b 100644
--- a/miscutils/make.c
+++ b/miscutils/make.c
@@ -2681,9 +2681,10 @@ expand_makeflags(void)
 }
 
 // These macros require special treatment
-#define MAKEFLAGS_SHELL "MAKEFLAGS\0SHELL\0"
+#define SPECIAL_MACROS "MAKEFLAGS\0SHELL\0CURDIR\0"
 #define MAKEFLAGS 0
 #define SHELL 1
+#define CURDIR 2
 
 /*
  * Instantiate all macros in an argv-style array of pointers.  Stop
@@ -2697,7 +2698,7 @@ process_macros(char **argv, int level)
         char *p;
 
         for (; *argv; argv++) {
-                int immediate = 0;
+                int idx, immediate = 0;
 
                 if (!(p = strchr(*argv, '='))) {
                         // Skip targets on the command line
@@ -2714,8 +2715,15 @@ process_macros(char **argv, int level)
                         immediate = M_IMMEDIATE;
                         p[-2] = '\0';
                 } else
-                *p = '\0';
-                if (level != 3 || index_in_strings(MAKEFLAGS_SHELL, *argv) < 0) {
+                        *p = '\0';
+
+                /* We want to process _most_ macro assignments.
+                 * There are exceptions for particular values from the
+                 * environment (level 3). */
+                idx = index_in_strings(SPECIAL_MACROS, *argv);
+                if (!(level == 3 &&
+                                (idx == MAKEFLAGS || idx == SHELL ||
+                                        (idx == CURDIR && !useenv && !POSIX_2017)))) {
                         if (immediate) {
                                 char *exp = expand_macros(p + 1, FALSE);
                                 setmacro(*argv, exp, level | immediate);
@@ -2724,6 +2732,7 @@ process_macros(char **argv, int level)
                                 setmacro(*argv, p + 1, level);
                         }
                 }
+
                 *p = '=';
                 if (immediate)
                         p[-2] = ':';
@@ -2766,7 +2775,7 @@ update_makeflags(void)
         for (i = 0; i < HTABSIZE; ++i) {
                 for (mp = macrohead[i]; mp; mp = mp->m_next) {
                         if (mp->m_level == 1 || mp->m_level == 2) {
-                                int idx = index_in_strings(MAKEFLAGS_SHELL, mp->m_name);
+                                int idx = index_in_strings(SPECIAL_MACROS, mp->m_name);
                                 if (idx == MAKEFLAGS)
                                         continue;
                                 macro = xzalloc(strlen(mp->m_name) + 2 * strlen(mp->m_val) + 1);
@@ -2960,6 +2969,20 @@ int make_main(int argc UNUSED_PARAM, char **argv)
 
         setmacro("SHELL", DEFAULT_SHELL, 4);
         setmacro("MAKE", path, 4);
+        if (!POSIX_2017) {
+                char *cwd = xrealloc_getcwd_or_warn(NULL);
+
+                if (cwd) {
+                        if (!useenv) {
+                                // Export cwd to environment, if necessary
+                                char *envcwd = getenv("CURDIR");
+                                if (envcwd && strcmp(cwd, envcwd) != 0)
+                                        setenv("CURDIR", cwd, 1);
+                        }
+                        setmacro("CURDIR", cwd, 4);
+                }
+                free(cwd);
+        }
         free((void *)newpath);
 
         if (!makefiles) {       // Look for a default Makefile
diff --git a/testsuite/make.tests b/testsuite/make.tests
index 546dca7d5..fdbb4ccfc 100755
--- a/testsuite/make.tests
+++ b/testsuite/make.tests
@@ -377,6 +377,31 @@ target:
 b}
 '
 
+# The CURDIR macro is supported in POSIX 202X.
+testing "make CURDIR macro" \
+        "make -f -" \
+        "OK\n" "" '
+target:
+        @test "$(CURDIR)" = "$$(pwd)" && echo OK
+'
+# The CURDIR environment variable doesn't affect the macro
+export CURDIR=/you/are/here
+testing "make CURDIR macro not affected by environment" \
+        "make -f -" \
+        "OK\n" "" '
+target:
+        @test "$(CURDIR)" != "/you/are/here" && echo OK
+'
+
+# The -e option makes the CURDIR macro match the environment
+testing "make with -e CURDIR macro is affected by the environment" \
+        "make -e -f -" \
+        "/you/are/here\n" "" '
+target:
+        @echo $(CURDIR)
+'
+unset CURDIR
+
 # POSIX 202X permits additional characters in macro and target names
 testing "make allow - and / in target names, - in macro names" \
         "make -f -" \