From 6f6ea12ebbd9251cc885a0720b0ec09fbc2d9331 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Tue, 19 Jul 2022 11:11:44 +0200
Subject: Warn about conditional dependency declarations during distribution

---
 libbuild2/parser.cxx | 42 ++++++++++++++++++++++++++++++++++++++++++
 libbuild2/parser.hxx |  9 +++++++++
 2 files changed, 51 insertions(+)

diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index cc8fd9e..84b6366 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -247,6 +247,8 @@ namespace build2
   {
     pre_parse_ = false;
     attributes_.clear ();
+    imported_ = false;
+    condition_ = nullopt;
     default_target_ = nullptr;
     peeked_ = false;
     replay_ = replay::stop;
@@ -2368,6 +2370,34 @@ namespace build2
     //
     tracer trace ("parser::parse_dependency", &path_);
 
+    // Diagnose conditional prerequisites. Note that we want to diagnose this
+    // even if pns is empty (think empty variable expansion; the literal "no
+    // prerequisites" case is handled elsewhere). We also want to omit this
+    // check for imported buildfiles (export stub can reasonably wrap loading
+    // of a buildfile in a condition).
+    //
+    // @@ TMP For now we only do it during the dist meta-operation. In the
+    //        future we should tighten this to any meta-operation provided
+    //        the dist module is loaded.
+    //
+    // @@ TMP For now it's a warning because we have dependencies like
+    //        cli.cxx{foo}: cli{foo} which are not currently possible to
+    //        rewrite (cli.cxx{} is not always registered).
+    //
+    if (condition_ &&
+        !imported_ &&
+        ctx->current_mif != nullptr &&
+        ctx->current_mif->id == dist_id)
+    {
+      warn (tloc) << "conditional dependency declaration may result in "
+                  << "incomplete distribution" <<
+        info (ploc) << "prerequisite declared here" <<
+        info (*condition_) << "conditional buildfile fragment starts here" <<
+        info << "instead use `include` prerequisite-specific variable to "
+             << "conditionally include prerequisites" <<
+        info << "for example: <target>: <prerequisite>: include = (<condition>)";
+    }
+
     // First enter all the targets.
     //
     small_vector<reference_wrapper<target>, 1> tgs (
@@ -3699,6 +3729,12 @@ namespace build2
   void parser::
   parse_if_else (token& t, type& tt)
   {
+    auto g = make_guard ([this, old = condition_] () mutable
+                         {
+                           condition_ = old;
+                         });
+    condition_ = get_location (t);
+
     parse_if_else (t, tt,
                    false /* multi */,
                    [this] (token& t, type& tt, bool s, const string& k)
@@ -3840,6 +3876,12 @@ namespace build2
   void parser::
   parse_switch (token& t, type& tt)
   {
+    auto g = make_guard ([this, old = condition_] () mutable
+                         {
+                           condition_ = old;
+                         });
+    condition_ = get_location (t);
+
     parse_switch (t, tt,
                   false /* multi */,
                   [this] (token& t, type& tt, bool s, const string& k)
diff --git a/libbuild2/parser.hxx b/libbuild2/parser.hxx
index f806568..61ecd5b 100644
--- a/libbuild2/parser.hxx
+++ b/libbuild2/parser.hxx
@@ -91,6 +91,12 @@ namespace build2
     parse_export_stub (istream& is, const path_name& name,
                        scope& rs, scope& bs)
     {
+      auto g = make_guard ([this, old = imported_] () mutable
+                           {
+                             imported_ = old;
+                           });
+      imported_ = true;
+
       parse_buildfile (is, name, &rs, bs);
       return move (export_value);
     }
@@ -906,6 +912,9 @@ namespace build2
 
     small_vector<attributes, 2> attributes_;
 
+    bool imported_ = false;        // True if loaded via export stub.
+    optional<location> condition_; // Innermost if/switch (but not in recipe).
+
     target* default_target_ = nullptr;
 
     replay_token peek_;
-- 
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