MINOR: config: add predicates "version_atleast" and "version_before" to cond blocks

These predicates respectively verify that the current version is at least
a given version or is before a specific one. The syntax is exactly the one
reported by "haproxy -v", though each component is optional, so both "1.5"
and "2.4-dev18-88910-48" are supported. Missing components equal zero, and
"dev" is below "pre" or "rc", which are both inferior to no such mention
(i.e. they are negative). Thus "2.4-dev18" is older than "2.4-rc1" which
is older than "2.4".

doc/configuration.txt

@@ -821,6 +821,16 @@ The list of currently supported predicates is the following:
   - streq(<str1>,<str2>)  : returns true only if the two strings are equal
   - strneq(<str1>,<str2>) : returns true only if the two strings differ
 
+  - version_atleast(<ver>): returns true if the current haproxy version is
+                            at least as recent as <ver> otherwise false. The
+                            version syntax is the same as shown by "haproxy -v"
+                            and missing components are assumed as being zero.
+
+  - version_before(<ver>) : returns true if the current haproxy version is
+                            strictly older than <ver> otherwise false. The
+                            version syntax is the same as shown by "haproxy -v"
+                            and missing components are assumed as being zero.
+
 Example:
 
    .if defined(HAPROXY_MWORKER)
@@ -839,6 +849,10 @@ Example:
      .endif
    .endif
 
+   .if version_atleast(2.4-dev19)
+       profiling.memory on
+   .endif
+
 Three other directives are provided to report some status:
 
   - .notice "message"  : emit this message at level NOTICE

src/cfgparse.c

@@ -140,6 +140,8 @@ enum cond_predicate {
 	CFG_PRED_FEATURE,         // "feature"
 	CFG_PRED_STREQ,           // "streq"
 	CFG_PRED_STRNEQ,          // "strneq"
+	CFG_PRED_VERSION_ATLEAST, // "version_atleast"
+	CFG_PRED_VERSION_BEFORE,  // "version_before"
 };
 
 struct cond_pred_kw {
@@ -154,6 +156,8 @@ const struct cond_pred_kw cond_predicates[] = {
 	{ "feature",          CFG_PRED_FEATURE,         ARG1(1, STR)         },
 	{ "streq",            CFG_PRED_STREQ,           ARG2(2, STR, STR)    },
 	{ "strneq",           CFG_PRED_STRNEQ,          ARG2(2, STR, STR)    },
+	{ "version_atleast",  CFG_PRED_VERSION_ATLEAST, ARG1(1, STR)         },
+	{ "version_before",   CFG_PRED_VERSION_BEFORE,  ARG1(1, STR)         },
 	{ NULL, CFG_PRED_NONE, 0 }
 };
 
@@ -1753,6 +1757,14 @@ static int cfg_eval_condition(char **args, char **err, const char **errptr)
 			ret = strcmp(argp[0].data.str.area, argp[1].data.str.area) != 0;
 			goto done;
 
+		case CFG_PRED_VERSION_ATLEAST: // checks if the current version is at least this one
+			ret = compare_current_version(argp[0].data.str.area) <= 0;
+			goto done;
+
+		case CFG_PRED_VERSION_BEFORE:  // checks if the current version is older than this one
+			ret = compare_current_version(argp[0].data.str.area) > 0;
+			goto done;
+
 		default:
 			memprintf(err, "internal error: unhandled conditional expression predicate '%s'", cond_pred->word);
 			if (errptr)