From 6845f5a8d8871e8dbc672b6dd11bd47bea02f19a Mon Sep 17 00:00:00 2001
From: q66 <daniel@octaforge.org>
Date: Tue, 1 May 2018 20:46:21 +0200
Subject: [PATCH] add a way to conditionally use rules according to predicate

---
 ostd/build/make.hh | 13 +++++++++++++
 src/build_make.cc  |  3 +++
 2 files changed, 16 insertions(+)

diff --git a/ostd/build/make.hh b/ostd/build/make.hh
index 019b838..ea5f567 100644
--- a/ostd/build/make.hh
+++ b/ostd/build/make.hh
@@ -118,6 +118,18 @@ struct make_rule {
         return *this;
     }
 
+    make_rule &cond(std::function<bool(string_range)> cond_f) noexcept {
+        p_cond = std::move(cond_f);
+        return *this;
+    }
+
+    bool cond(string_range target) const {
+        if (!p_cond) {
+            return true;
+        }
+        return p_cond(target);
+    }
+
     iterator_range<std::string const *> depends() const noexcept {
         return iterator_range<std::string const *>(
             p_deps.data(), p_deps.data() + p_deps.size()
@@ -159,6 +171,7 @@ private:
     make_pattern p_target;
     std::vector<std::string> p_deps{};
     body_func p_body{};
+    std::function<bool(string_range)> p_cond{};
     bool p_action = false;
 };
 
diff --git a/src/build_make.cc b/src/build_make.cc
index 30ee49f..4f652b8 100644
--- a/src/build_make.cc
+++ b/src/build_make.cc
@@ -176,6 +176,9 @@ void make::find_rules(string_range target, std::vector<rule_inst> &rlist) {
     rule_inst *frule = nullptr;
     std::size_t pfnl = 0, psubl = 0;
     for (auto &rule: p_rules) {
+        if (!rule.cond(target)) {
+            continue;
+        }
         auto &tgt = rule.target();
         auto [fnl, subl] = tgt.match(target);
         if ((fnl + subl) > 0) {