param: Expand %d to the default cc_command

This is useful for shell script wrappers that can take the original
command as an argument as well as the %{o,s,w} expansions as additional
parameters.

bin/varnishd/mgt/mgt.h

@@ -233,6 +233,7 @@ void mgt_vcl_startup(struct cli *, const char *vclsrc, const char *origin,
 int mgt_push_vcls(struct cli *, unsigned *status, char **p);
 const char *mgt_has_vcl(void);
 extern char *mgt_cc_cmd;
+extern char *mgt_cc_cmd_def;
 extern char *mgt_cc_warn;
 extern const char *mgt_vcl_path;
 extern const char *mgt_vmod_path;

bin/varnishd/mgt/mgt_param.c

@@ -765,6 +765,9 @@ MCF_InitParams(struct cli *cli)
 		mcf_wash_param(cli, pp, MCF_DEFAULT, "default", vsb);
 	}
 	VSB_destroy(&vsb);
+
+	AN(mgt_cc_cmd);
+	REPLACE(mgt_cc_cmd_def, mgt_cc_cmd);
 }
 
 /*--------------------------------------------------------------------*/

bin/varnishd/mgt/mgt_vcc.c

@@ -63,6 +63,7 @@ struct vcc_priv {
 };
 
 char *mgt_cc_cmd;
+char *mgt_cc_cmd_def;
 char *mgt_cc_warn;
 const char *mgt_vcl_path;
 const char *mgt_vmod_path;
@@ -154,6 +155,9 @@ run_cc(void *priv)
 			case 'w':
 				VSB_cat(sb, mgt_cc_warn);
 				break;
+			case 'd':
+				VSB_cat(sb, mgt_cc_cmd_def);
+				break;
 			case '%':
 				VSB_putc(sb, '%');
 				break;

bin/varnishtest/tests/c00109.vtc

 varnishtest "cc_command and cc_warnings"
 
 varnish v1 -cliok {param.set debug +vcl_keep}
-varnish v1 -cliok {param.set cc_command "! printf '%w' >world"}
 varnish v1 -cliok {param.set cc_warnings hello}
+varnish v1 -cliok {param.set cc_command << EOF
+! printf 'd="%%s" w="%%s"' '%d' '%w' >world
+EOF}
 
 varnish v1 -errvcl "VCL compilation failed" "backend be none;"
 
-shell -expect hello "cat v1/vcl_*/world"
+shell -match {d=".+" w="hello"} "cat v1/vcl_*/world"

include/tbl/params.h

@@ -1534,7 +1534,8 @@ PARAM_STRING(
 	"dlopen(3) loadable object.  Any occurrence of %s in "
 	"the string will be replaced with the source file name, "
 	"%o will be replaced with the output file name, and %w "
-	"will be replaced by the cc_warnings parameter.",
+	"will be replaced by the cc_warnings parameter. The %d "
+	"sequence expands to the default value for cc_command.",
 	/* flags */	MUST_RELOAD | BUILD_OPTIONS,
 	/* dyn_min_reason */	NULL,
 	/* dyn_max_reason */	NULL,