Give hints for common causes of "no rule to update ..." error

12 files changed, 121 insertions, 50 deletions

diff --git a/libbuild2/algorithm.cxx b/libbuild2/algorithm.cxx
index 5b340c7..53aac4e 100644
--- a/libbuild2/algorithm.cxx
+++ b/libbuild2/algorithm.cxx
@@ -298,7 +298,7 @@ namespace build2
                                    out,
                                    move (n),
                                    nullopt /* ext     */,
-                                   true    /* implied */,
+                                   target_decl::implied,
                                    trace));
 
     assert (r.second.owns_lock ());
@@ -509,6 +509,55 @@ namespace build2
       diag_record dr;
       dr << fail << "no rule to " << diag_do (a, t);
 
+      // Try to give some hints of the common causes.
+      //
+      switch (t.decl)
+      {
+      case target_decl::prereq_new:
+        {
+          dr << info << "target " << t << " is no declared in any buildfile";
+
+          if (t.is_a<file> ())
+            dr << info << "perhaps it is a missing source file?";
+
+          break;
+        }
+      case target_decl::prereq_file:
+        {
+          // It's an existing file so it's an unlikely case.
+          //
+          break;
+        }
+      case target_decl::implied:
+        {
+          // While the "in a buildfile" is not exactly accurate, we assume
+          // it's unlikely we will end up here in other cases.
+          //
+          dr << info << "target " << t << " is implicitly declared in a "
+             << "buildfile";
+
+          if (const scope* rs = bs.root_scope ())
+          {
+            if (t.out.empty () && rs->src_path () != rs->out_path ())
+            {
+              name n (t.as_name ()[0]);
+              n.dir.clear ();
+              dr << info << "perhaps it should be declared as being in the "
+                 << "source tree: " << n << "@./ ?";
+            }
+          }
+
+          break;
+        }
+      case target_decl::real:
+        {
+          // If we had a location, maybe it would make sense to mention this
+          // case.
+          //
+          break;
+        }
+      }
+
       if (verb < 4)
         dr << info << "re-run with --verbose=4 for more information";
     }
diff --git a/libbuild2/bash/rule.cxx b/libbuild2/bash/rule.cxx
index 0df9792..148da95 100644
--- a/libbuild2/bash/rule.cxx
+++ b/libbuild2/bash/rule.cxx
@@ -161,7 +161,7 @@ namespace build2
                                                         dir_path () /* out */,
                                                         p.name,
                                                         ext,
-                                                        true /* implied */,
+                                                        target_decl::implied,
                                                         trace));
 
                   bash& pt (rp.first.as<bash> ());
diff --git a/libbuild2/cc/common.txx b/libbuild2/cc/common.txx
index bfbc52c..ce922cc 100644
--- a/libbuild2/cc/common.txx
+++ b/libbuild2/cc/common.txx
@@ -24,7 +24,7 @@ namespace build2
                                          path_cast<dir_path> (out.effect),
                                          name,
                                          move (ext),
-                                         true, // Implied.
+                                         target_decl::implied,
                                          trace));
 
       assert (!exist || !p.second.owns_lock ());
diff --git a/libbuild2/cc/compile-rule.cxx b/libbuild2/cc/compile-rule.cxx
index 37daf76..d568883 100644
--- a/libbuild2/cc/compile-rule.cxx
+++ b/libbuild2/cc/compile-rule.cxx
@@ -5500,7 +5500,7 @@ namespace build2
                 dir_path (), // Always in the out tree.
                 move (mf),
                 nullopt,     // Use default extension.
-                true,        // Implied.
+                target_decl::implied,
                 trace));
       file& bt (static_cast<file&> (p.first));
 
@@ -5571,7 +5571,7 @@ namespace build2
                 dir_path (), // Always in the out tree.
                 move (mf),
                 nullopt,     // Use default extension.
-                true,        // Implied.
+                target_decl::implied,
                 trace));
       file& bt (static_cast<file&> (p.first));
 
diff --git a/libbuild2/cc/pkgconfig.cxx b/libbuild2/cc/pkgconfig.cxx
index 7e74c24..516746b 100644
--- a/libbuild2/cc/pkgconfig.cxx
+++ b/libbuild2/cc/pkgconfig.cxx
@@ -1152,7 +1152,7 @@ namespace build2
               dir_path (),
               mf.base ().string (),
               mf.extension (),
-              true, // Implied.
+              target_decl::implied,
               trace));
 
           target& mt (tl.first);
diff --git a/libbuild2/config/operation.cxx b/libbuild2/config/operation.cxx
index 963a3e1..b9856be 100644
--- a/libbuild2/config/operation.cxx
+++ b/libbuild2/config/operation.cxx
@@ -1083,7 +1083,7 @@ namespace build2
                                    dir_path (), // Out tree.
                                    "",
                                    nullopt,
-                                   true,       // Implied.
+                                   target_decl::implied,
                                    trace).first);
 
           if (verb != 0 && diag >= 2)
diff --git a/libbuild2/file.cxx b/libbuild2/file.cxx
index 14b16a7..1bd5068 100644
--- a/libbuild2/file.cxx
+++ b/libbuild2/file.cxx
@@ -1660,7 +1660,7 @@ namespace build2
                                  dir_path (),    // No out (not in project).
                                  p.leaf ().base ().string (),
                                  p.extension (), // Always specified.
-                                 true /* implied */,
+                                 target_decl::implied,
                                  trace));
 
     if (const file* f = r.first.is_a<file> ())
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index 8ae13a8..033395d 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -150,13 +150,14 @@ namespace build2
                    tracer& tr)
     {
       auto r (p.scope_->find_target_type (n, o, loc));
-      return p.ctx.targets.insert (r.first,         // target type
-                                   move (n.dir),
-                                   move (o.dir),
-                                   move (n.value),
-                                   move (r.second), // extension
-                                   implied,
-                                   tr).first;
+      return p.ctx.targets.insert (
+        r.first,         // target type
+        move (n.dir),
+        move (o.dir),
+        move (n.value),
+        move (r.second), // extension
+        implied ? target_decl::implied : target_decl::real,
+        tr).first;
     }
 
     // Only find.
@@ -1076,10 +1077,10 @@ namespace build2
 
     // If we have a recipe, the target is not implied.
     //
-    if (target_->implied)
+    if (target_->decl != target_decl::real)
     {
       for (target* m (target_); m != nullptr; m = m->adhoc_member)
-        m->implied = false;
+        m->decl = target_decl::real;
 
       if (default_target_ == nullptr)
         default_target_ = target_;
@@ -6894,7 +6895,7 @@ namespace build2
     target& dt (*default_target_);
 
     target* ct (
-      const_cast<target*> (                // Ok (serial execution).
+      const_cast<target*> (                    // Ok (serial execution).
         ctx.targets.find (dir::static_type,    // Explicit current dir target.
                           scope_->out_path (),
                           dir_path (),         // Out tree target.
@@ -6914,13 +6915,13 @@ namespace build2
                                 dir_path (),
                                 string (),
                                 nullopt,
-                                false,
+                                target_decl::real,
                                 trace).first;
       // Fall through.
     }
-    else if (ct->implied)
+    else if (ct->decl != target_decl::real)
     {
-      ct->implied = false;
+      ct->decl = target_decl::real;
       // Fall through.
     }
     else
diff --git a/libbuild2/search.cxx b/libbuild2/search.cxx
index 8f5410c..2b10e0b 100644
--- a/libbuild2/search.cxx
+++ b/libbuild2/search.cxx
@@ -183,9 +183,13 @@ namespace build2
 
     // Find or insert. Note that we are using our updated extension.
     //
-    auto r (
-      ctx.targets.insert (
-        *tk.type, move (d), move (out), *tk.name, ext, true, trace));
+    auto r (ctx.targets.insert (*tk.type,
+                                move (d),
+                                move (out),
+                                *tk.name,
+                                ext,
+                                target_decl::prereq_file,
+                                trace));
 
     // Has to be a file_target.
     //
@@ -231,7 +235,7 @@ namespace build2
                                 *tk.out,
                                 *tk.name,
                                 tk.ext,
-                                true /* implied */,
+                                target_decl::prereq_new,
                                 trace));
 
     const target& t (r.first);
diff --git a/libbuild2/target.cxx b/libbuild2/target.cxx
index 7327b1b..8d76f56 100644
--- a/libbuild2/target.cxx
+++ b/libbuild2/target.cxx
@@ -412,7 +412,7 @@ namespace build2
                  dir_path out,
                  string name,
                  optional<string> ext,
-                 bool implied,
+                 target_decl decl,
                  tracer& trace)
   {
     target_key tk {&tt, &dir, &out, &name, move (ext)};
@@ -447,7 +447,7 @@ namespace build2
       if (p.second)
       {
         t->ext_ = &i->first.ext;
-        t->implied = implied;
+        t->decl = decl;
         t->state.inner.target_ = t;
         t->state.outer.target_ = t;
         return pair<target&, ulock> (*t, move (ul));
@@ -484,16 +484,12 @@ namespace build2
       // Fall through (continue as if the first find() returned this target).
     }
 
-    if (!implied)
+    if (decl > t->decl)
     {
-      // The implied flag can only be cleared during the load phase.
+      // The decl value can only be adjusted during the load phase.
       //
       assert (ctx.phase == run_phase::load);
-
-      // Clear the implied flag.
-      //
-      if (t->implied)
-        t->implied = false;
+      t->decl = decl;
     }
 
     return pair<target&, ulock> (*t, ulock ());
@@ -833,7 +829,7 @@ namespace build2
     //
     const target* e (search_existing_target (t.ctx, pk));
 
-    if (e == nullptr || e->implied)
+    if (e == nullptr || e->decl != target_decl::real)
       fail << "no explicit target for " << pk;
 
     return e;
@@ -928,7 +924,7 @@ namespace build2
     //
     const target* e (search_existing_target (t.ctx, pk));
 
-    if (e != nullptr && !e->implied)
+    if (e != nullptr && e->decl == target_decl::real)
       return e;
 
     // If not found (or is implied), then try to load the corresponding
@@ -977,7 +973,7 @@ namespace build2
       if (e == nullptr)
         e = search_existing_target (t.ctx, pk);
 
-      if (e != nullptr && !e->implied)
+      if (e != nullptr && e->decl == target_decl::real)
         retest = true;
       else
       {
@@ -1018,7 +1014,7 @@ namespace build2
       if (e == nullptr)
         e = search_existing_target (t.ctx, pk);
 
-      if (e != nullptr && !e->implied)
+      if (e != nullptr && e->decl == target_decl::real)
         return e;
     }
 
diff --git a/libbuild2/target.hxx b/libbuild2/target.hxx
index 17a99d3..ec97950 100644
--- a/libbuild2/target.hxx
+++ b/libbuild2/target.hxx
@@ -99,6 +99,31 @@ namespace build2
 
   // Target.
   //
+
+  // A target can be entered for several reasons that are useful to
+  // distinguish for diagnostics, when considering as the default
+  // target, etc.
+  //
+  // Note that the order of the enumerators is arranged so that their
+  // integral values indicate whether one "overrides" the other.
+  //
+  // @@ We have cases (like pkg-config extraction) where it should probably be
+  //    prereq_file rather than implied (also audit targets.insert<> calls).
+  //
+  enum class target_decl: uint8_t
+  {
+    prereq_new,  // Created from prerequisite (create_new_target()).
+    prereq_file, // Created from prerequisite/file (search_existing_file ()).
+    implied,     // Target-spec variable assignment, implicitly-entered, etc.
+    real         // Real dependency declaration.
+  };
+
+  inline bool
+  operator> (target_decl l, target_decl r)
+  {
+    return static_cast<uint8_t> (l) > static_cast<uint8_t> (r);
+  }
+
   class LIBBUILD2_SYMEXPORT target
   {
   public:
@@ -131,14 +156,10 @@ namespace build2
     const dir_path&
     out_dir () const {return out.empty () ? dir : out;}
 
-    // A target that is not (yet) entered as part of a real dependency
-    // declaration (for example, that is entered as part of a target-specific
-    // variable assignment, dependency extraction, etc) is called implied.
-    //
-    // The implied flag should only be cleared during the load phase via the
-    // MT-safe target_set::insert().
+    // Note that the declaration should only be upgraded during the load phase
+    // via the MT-safe target_set::insert().
     //
-    bool implied;
+    target_decl decl;
 
     // Target group to which this target belongs, if any. Note that we assume
     // that the group and all its members are in the same scope (for example,
@@ -1349,7 +1370,7 @@ namespace build2
                    dir_path out,
                    string name,
                    optional<string> ext,
-                   bool implied,
+                   target_decl,
                    tracer&);
 
     pair<target&, bool>
@@ -1358,7 +1379,7 @@ namespace build2
             dir_path out,
             string name,
             optional<string> ext,
-            bool implied,
+            target_decl decl,
             tracer& t)
     {
       auto p (insert_locked (tt,
@@ -1366,7 +1387,7 @@ namespace build2
                              move (out),
                              move (name),
                              move (ext),
-                             implied,
+                             decl,
                              t));
 
       return pair<target&, bool> (p.first, p.second.owns_lock ());
@@ -1388,7 +1409,7 @@ namespace build2
                      move (out),
                      move (name),
                      move (ext),
-                     true,
+                     target_decl::implied,
                      t).first.template as<T> ();
     }
 
diff --git a/libbuild2/target.txx b/libbuild2/target.txx
index d304daa..fb9fe9c 100644
--- a/libbuild2/target.txx
+++ b/libbuild2/target.txx
@@ -176,7 +176,7 @@ namespace build2
                                       dir_path (),
                                       string (),
                                       nullopt,
-                                      false,
+                                      target_decl::real,
                                       trace).first);
     t.prerequisites (move (ps));
     return &t;