make: changes to .DEFAULT/inference rules

The POSIX standard allows inference rules to be redefined but not
the .DEFAULT rule.  There is no explicit exception for .DEFAULT to:

   Only one target rule for any given target can contain commands.

Treat redefinition of a .DEFAULT rule as an error in POSIX mode
but allow it as an extension.

Also, the code didn't allow an inference rule with dependencies to
redefine an existing inference rule.  This is no longer the case.

Adds 64-96 bytes.

2 files changed, 38 insertions, 19 deletions

diff --git a/miscutils/make.c b/miscutils/make.c
index cc5e7ca92..df810677f 100644
--- a/miscutils/make.c
+++ b/miscutils/make.c
@@ -188,6 +188,7 @@ struct name {
 #define N_SPECIAL       0x80    // Special target
 #define N_MARK          0x100   // Mark for deduplication
 #define N_PHONY         0x200   // Name is a phony target
+#define N_INFERENCE     0x400   // Inference rule
 
 // List of rules to build a target
 struct rule {
@@ -736,7 +737,10 @@ addrule(struct name *np, struct depend *dp, struct cmd *cp, int flag)
 
         if (cp && !(np->n_flag & N_DOUBLE) && getcmd(np)) {
                 // Handle the inference rule redefinition case
-                if ((np->n_flag & N_SPECIAL) && !dp) {
+                // .DEFAULT rule can also be redefined (as an extension).
+                if ((np->n_flag & N_INFERENCE)
+                                && !(posix && (np->n_flag & N_SPECIAL))
+                ) {
                         freerules(np->n_rule);
                         np->n_rule = NULL;
                 } else {
@@ -2343,12 +2347,19 @@ input(FILE *fd, int ilevel)
 
                                 np = newname(files[i]);
                                 if (ttype != T_NORMAL) {
-                                        if (ttype == T_INFERENCE && posix) {
-                                                if (semicolon_cmd)
-                                                        error_in_inference_rule("'; command'");
-                                                seen_inference = TRUE;
+                                        if (ttype == T_INFERENCE) {
+                                                if (posix) {
+                                                        if (semicolon_cmd)
+                                                                error_in_inference_rule("'; command'");
+                                                        seen_inference = TRUE;
+                                                }
+                                                np->n_flag |= N_INFERENCE;
+                                        } else if (strcmp(p, ".DEFAULT") == 0) {
+                                                // .DEFAULT rule is a special case
+                                                np->n_flag |= N_SPECIAL | N_INFERENCE;
+                                        } else {
+                                                np->n_flag |= N_SPECIAL;
                                         }
-                                        np->n_flag |= N_SPECIAL;
                                 } else if (!firstname) {
                                         firstname = np;
                                 }
@@ -2358,7 +2369,7 @@ input(FILE *fd, int ilevel)
                         if (files != &p)
                                 globfree(&gd);
                 }
-                if (seen_inference && count != 1)
+                if (posix && seen_inference && count != 1)
                         error_in_inference_rule("multiple targets");
 
                 // Prerequisites and commands will be unused if there were
diff --git a/testsuite/make.tests b/testsuite/make.tests
index a12e50b8b..376bdcc15 100755
--- a/testsuite/make.tests
+++ b/testsuite/make.tests
@@ -12,18 +12,6 @@ target:
         @echo target
 '
 
-# .DEFAULT rules with no commands or some prerequisites are ignored.
-# .DEFAULT rules with commands can be redefined.
-testing "make .DEFAULT rule" \
-        "make -f - default" "default2\n" "" '
-.DEFAULT: ignored
-.DEFAULT:
-        @echo default1
-.DEFAULT:
-        @echo default2
-target:
-'
-
 testing "make .DEFAULT rule for prerequisite" \
         "make -f - 2>/dev/null" "source\n" "" '
 .DEFAULT:
@@ -721,6 +709,26 @@ target:: file2 file3 file3
 '
 cd .. || exit 1; rm -rf make.tempdir 2>/dev/null
 
+# .DEFAULT rules with no commands or some prerequisites are ignored.
+# .DEFAULT rules with commands can be redefined.
+testing "make: .DEFAULT rule" \
+        "make -f - default" "default2\n" "" '
+.DEFAULT: ignored
+.DEFAULT:
+        @echo default1
+.DEFAULT:
+        @echo default2
+target:
+'
+
+testing "make: double-colon rule" \
+        "make -f -" "target1\ntarget2\n" "" '
+target::
+        @echo target1
+target::
+        @echo target2
+'
+
 # Double-colon rules didn't work properly if their target was phony:
 # - they didn't ignore the presence of a file matching the target name;
 # - they were also invoked as if they were a single-colon rule.