Add support for default extension specification, trailing dot escaping

For example:

cxx{*}: extension = cxx

cxx{foo}         # foo.cxx
cxx{foo.test}    # foo.test      (probably what we want...)
cxx{foo.test...} # foo.test.cxx  (... is this)
cxx{foo..}       # foo.
cxx{foo....}     # foo..
cxx{foo.....}    # error (must come in escape pair)

14 files changed, 372 insertions, 179 deletions

diff --git a/build2/algorithm.cxx b/build2/algorithm.cxx
index 550a491..bfe6943 100644
--- a/build2/algorithm.cxx
+++ b/build2/algorithm.cxx
@@ -49,8 +49,9 @@ namespace build2
   {
     assert (phase == run_phase::match);
 
-    optional<string> ext;
-    const target_type* tt (s.find_target_type (n, ext, location ()));
+    auto rp (s.find_target_type (n, location ()));
+    const target_type* tt (rp.first);
+    optional<string>& ext (rp.second);
 
     if (tt == nullptr)
       fail << "unknown target type " << n.type << " in name " << n;
@@ -77,8 +78,9 @@ namespace build2
     assert (phase == run_phase::match || phase == run_phase::execute);
 
     name n (cn);
-    optional<string> ext;
-    const target_type* tt (s.find_target_type (n, ext, location ()));
+    auto rp (s.find_target_type (n, location ()));
+    const target_type* tt (rp.first);
+    optional<string>& ext (rp.second);
 
     // For now we treat an unknown target type as an unknown target. Seems
     // logical.
diff --git a/build2/b.cxx b/build2/b.cxx
index de4ee0c..aedda7f 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -694,8 +694,9 @@ main (int argc, char* argv[])
             const string& v (tn.value);
 
             // Handle a few common cases as special: empty name, '.', '..', as
-            // well as dir{foo/bar} (without trailing '/'). This code must be
-            // consistent with find_target_type() and other places.
+            // well as dir{foo/bar} (without trailing '/'). This logic must be
+            // consistent with find_target_type() and other places (grep for
+            // "..").
             //
             if (v.empty () || v == "." || v == ".." || tn.type == "dir")
               out_base = dir_path (v);
@@ -1274,10 +1275,11 @@ main (int argc, char* argv[])
 
           // Find the target type and extract the extension.
           //
-          optional<string> e;
-          const target_type* ti (bs.find_target_type (tn, e, l));
+          auto rp (bs.find_target_type (tn, l));
+          const target_type* tt (rp.first);
+          optional<string>& e (rp.second);
 
-          if (ti == nullptr)
+          if (tt == nullptr)
             fail (l) << "unknown target type " << tn.type;
 
           if (mif->search != nullptr)
@@ -1303,7 +1305,7 @@ main (int argc, char* argv[])
 
             mif->search (mparams,
                          rs, bs,
-                         target_key {ti, &d, &out, &tn.value, e},
+                         target_key {tt, &d, &out, &tn.value, e},
                          l,
                          tgs);
           }
diff --git a/build2/cc/common.cxx b/build2/cc/common.cxx
index ca73483..c6ef3bd 100644
--- a/build2/cc/common.cxx
+++ b/build2/cc/common.cxx
@@ -431,11 +431,9 @@ namespace build2
       {
         // This is import.
         //
-        optional<string> ext;
-
-        // Changes name.
-        //
-        const target_type* tt (s.find_target_type (n, ext, location ()));
+        auto rp (s.find_target_type (n, location ())); // Note: changes name.
+        const target_type* tt (rp.first);
+        optional<string>& ext (rp.second);
 
         if (tt == nullptr)
           fail << "unknown target type '" << n.type << "' in library " << n;
diff --git a/build2/config/operation.cxx b/build2/config/operation.cxx
index f9e9253..accae17 100644
--- a/build2/config/operation.cxx
+++ b/build2/config/operation.cxx
@@ -931,8 +931,8 @@ namespace build2
         {
           const name& tn (ts.name);
 
-          // Figure out the project directory. This code must be consistent
-          // with find_target_type() and other places.
+          // Figure out the project directory. This logic must be consistent
+          // with find_target_type() and other places (grep for "..").
           //
           dir_path d;
 
diff --git a/build2/in/target.cxx b/build2/in/target.cxx
index fec1135..4bc9d6a 100644
--- a/build2/in/target.cxx
+++ b/build2/in/target.cxx
@@ -34,7 +34,11 @@ namespace build2
     }
 
     static bool
-    in_pattern (const target_type&, const scope&, string&, bool)
+    in_pattern (const target_type&,
+                const scope&,
+                string&,
+                optional<string>&,
+                bool)
     {
       fail << "pattern in in{} prerequisite" << endf;
     }
diff --git a/build2/parser.cxx b/build2/parser.cxx
index 57c7fc9..25742d0 100644
--- a/build2/parser.cxx
+++ b/build2/parser.cxx
@@ -149,10 +149,9 @@ namespace build2
                     name& o,
                     const location& loc)
     {
-      optional<string> e;
-      const target_type* ti (p.scope_->find_target_type (n, e, loc));
+      auto r (p.scope_->find_target_type (n, loc));
 
-      if (ti == nullptr)
+      if (r.first == nullptr)
         p.fail (loc) << "unknown target type " << n.type;
 
       bool src (n.pair); // If out-qualified, then it is from src.
@@ -187,7 +186,7 @@ namespace build2
       }
       o.dir = move (out); // Result.
 
-      return make_pair (ti, move (e));
+      return r;
     }
 
     ~enter_target ()
@@ -740,10 +739,11 @@ namespace build2
             //
             for (auto& pn: pns)
             {
-              optional<string> e;
-              const target_type* ti (scope_->find_target_type (pn, e, ploc));
+              auto rp (scope_->find_target_type (pn, ploc));
+              const target_type* tt (rp.first);
+              optional<string>& e (rp.second);
 
-              if (ti == nullptr)
+              if (tt == nullptr)
                 fail (ploc) << "unknown target type " << pn.type;
 
               // Current dir collapses to an empty one.
@@ -762,7 +762,7 @@ namespace build2
               // path.
               //
               prerequisite p (pn.proj,
-                              *ti,
+                              *tt,
                               move (pn.dir),
                               dir_path (),
                               move (pn.value),
@@ -2955,16 +2955,29 @@ namespace build2
       return butl::path_match (pattern, p, *sp);
     };
 
-    // Append string to result according to dir. Store an indication of
-    // whether it was amended in the pair flag.
+    // Append name/extension to result according to dir. Store an indication
+    // of whether it was amended as well as whether the extension is present
+    // in the pair flag. The extension itself is stored in name::type.
     //
-    auto append = [&r, &dir] (string&& v, bool a)
+    auto append = [&r, &dir] (string&& v, optional<string>&& e, bool a)
     {
-      r.push_back (dir ? name (dir_path (move (v))) : name (move (v)));
-      r.back ().pair = a ? 'a' : '\0';
+      name n (dir ? name (dir_path (move (v))) : name (move (v)));
+
+      if (a)
+        n.pair |= 0x01;
+
+      if (e)
+      {
+        n.type = move (*e);
+        n.pair |= 0x02;
+      }
+
+      r.push_back (move (n));
     };
 
-    auto include_match = [&r, &equal, &append] (string&& m, bool a)
+    auto include_match = [&r, &equal, &append] (string&& m,
+                                                optional<string>&& e,
+                                                bool a)
     {
       auto i (find_if (
                 r.begin (),
@@ -2972,11 +2985,13 @@ namespace build2
                 [&m, &equal] (const name& n) {return equal (m, n);}));
 
       if (i == r.end ())
-        append (move (m), a);
+        append (move (m), move (e), a);
     };
 
     auto include_pattern =
-      [&r, &append, &include_match, sp, &l, this] (string&& p, bool a)
+      [&r, &append, &include_match, sp, &l, this] (string&& p,
+                                                   optional<string>&& e,
+                                                   bool a)
     {
       // If we don't already have any matches and our pattern doesn't contain
       // multiple recursive wildcards, then the result will be unique and we
@@ -2990,38 +3005,39 @@ namespace build2
         unique = (i == string::npos || p.find ("**", i + 2) == string::npos);
       }
 
-      function<bool (path&&, const string&, bool)> func;
+      function<void (string&&, optional<string>&&)> appf;
       if (unique)
-        func = [a, &append] (path&& m, const string& p, bool interm)
+        appf = [a, &append] (string&& v, optional<string>&& e)
           {
-            // Ignore entries that start with a dot unless the pattern that
-            // matched them also starts with a dot.
-            //
-            const string& s (m.string ());
-            if (p[0] != '.' && s[path::traits::find_leaf (s)] == '.')
-              return !interm;
-
-            if (!interm)
-              append (move (m).representation (), a);
-
-            return true;
+            append (move (v), move (e), a);
           };
       else
-        func = [a, &include_match] (path&& m, const string& p, bool interm)
+        appf = [a, &include_match] (string&& v, optional<string>&& e)
           {
-            const string& s (m.string ());
-            if (p[0] != '.' && s[path::traits::find_leaf (s)] == '.')
-              return !interm;
+            include_match (move (v), move (e), a);
+          };
 
-            if (!interm)
-              include_match (move (m).representation (), a);
+      auto process = [&e, &appf] (path&& m, const string& p, bool interm)
+      {
+        // Ignore entries that start with a dot unless the pattern that
+        // matched them also starts with a dot.
+        //
+        const string& s (m.string ());
+        if (p[0] != '.' && s[path::traits::find_leaf (s)] == '.')
+          return !interm;
 
-            return true;
-          };
+        // Note that we have to make copies of the extension since there will
+        // multiple entries for each pattern.
+        //
+        if (!interm)
+          appf (move (m).representation (), optional<string> (e));
+
+        return true;
+      };
 
       try
       {
-        butl::path_search (path (move (p)), func, *sp);
+        butl::path_search (path (move (p)), process, *sp);
       }
       catch (const system_error& e)
       {
@@ -3058,7 +3074,7 @@ namespace build2
 
     // Process the pattern and inclusions/exclusions.
     //
-    for (auto b (pat.begin ()), i (b), e (pat.end ()); i != e; ++i)
+    for (auto b (pat.begin ()), i (b), end (pat.end ()); i != end; ++i)
     {
       name& n (*i);
       bool first (i == b);
@@ -3086,7 +3102,30 @@ namespace build2
       if (n.empty () || !(n.simple () || n.directory ()))
         fail (l) << "invalid '" << n << "' in " << what << " pattern";
 
-      string v (n.simple () ? move (n.value) : move (n.dir).representation ());
+      // Name splitting must be consistent with scope::find_target_type().
+      //
+      string v;
+      optional<string> e;
+      {
+        // Based on the first pattern figure out if the result is a directory
+        // or a file. For inclusions/exclusions verify it is consistent.
+        //
+        bool d (n.directory ());
+
+        if (first)
+          dir = d;
+        else if (d != dir)
+          fail (l) << "inconsistent file/directory result in " << what
+                   << " pattern";
+
+        if (d)
+          v = move (n.dir).representation ();
+        else
+        {
+          v = move (n.value);
+          e = target::split_name (v, l);
+        }
+      }
 
       // Figure out if this is inclusion or exclusion.
       //
@@ -3107,24 +3146,21 @@ namespace build2
       //
       bool a (tt != nullptr &&
               tt->pattern != nullptr &&
-              tt->pattern (*tt, *scope_, v, false));
+              tt->pattern (*tt, *scope_, v, e, false));
 
       // Figure out if this is a pattern.
       //
       bool p (v.find_first_of ("*?") != string::npos);
       assert (p || !first); // First must be a pattern.
 
-      // Based on the first pattern figure out if the result is a directory or
-      // a file. For inclusions/exclusions verify it is consistent.
+      // Factor non-empty extension back into the name.
       //
+      // Note that we don't support extension patterns.
+      //
+      if (e && !e->empty ())
       {
-        bool d (path::traits::is_separator (v.back ()));
-
-        if (first)
-          dir = d;
-        else if (d != dir)
-          fail (l) << "inconsistent file/directory result in " << what
-                   << " pattern";
+        v += '.';
+        v += *e;
       }
 
       try
@@ -3132,16 +3168,16 @@ namespace build2
         if (s == '+')
         {
           if (p)
-            include_pattern (move (v), a);
+            include_pattern (move (v), move (e), a);
           else
-            include_match (move (v), a);
+            include_match (move (v), move (e), a);
         }
         else
         {
           if (p)
             exclude_pattern (move (v));
           else
-            exclude_match (v);
+            exclude_match (move (v));
         }
       }
       catch (const invalid_path& e)
@@ -3151,26 +3187,45 @@ namespace build2
       }
     }
 
-    // Reverse target type-specific pattern/match amendments from the result.
-    // Essentially: cxx{*} -> *.cxx -> foo.cxx -> cxx{foo}.
+    // Post-process the result: remove extension, reverse target type-specific
+    // pattern/match amendments (essentially: cxx{*} -> *.cxx -> foo.cxx ->
+    // cxx{foo}), and recombined the result.
     //
-    if (tt != nullptr && tt->pattern != nullptr)
+    for (name& n: r)
     {
-      for (name& n: r)
+      string v;
+      optional<string> e;
+
+      if (dir)
+        v = move (n.dir).representation ();
+      else
       {
-        if (n.pair)
-        {
-          string v (dir ? move (n.dir).representation () : move (n.value));
-          tt->pattern (*tt, *scope_, v, true);
+        v = move (n.value);
 
-          if (dir)
-            n.dir = dir_path (move (v));
-          else
-            n.value = move (v);
+        if ((n.pair & 0x02) != 0)
+        {
+          e = move (n.type);
 
-          n.pair = '\0';
+          // Remove non-empty extension from the name (it got to be there, see
+          // above).
+          //
+          if (!e->empty ())
+            v.resize (v.size () - e->size () - 1);
         }
       }
+
+      if ((n.pair & 0x01) != 0)
+        tt->pattern (*tt, *scope_, v, e, true);
+
+      if (dir)
+        n.dir = dir_path (move (v));
+      else
+      {
+        target::combine_name (v, e);
+        n.value = move (v);
+      }
+
+      n.pair = '\0';
     }
 
     return splice_names (
diff --git a/build2/scope.cxx b/build2/scope.cxx
index dc08925..bf83830 100644
--- a/build2/scope.cxx
+++ b/build2/scope.cxx
@@ -588,36 +588,38 @@ namespace build2
     return nullptr;
   }
 
-  const target_type* scope::
-  find_target_type (name& n, optional<string>& ext, const location& loc) const
+  pair<const target_type*, optional<string>> scope::
+  find_target_type (name& n, const location& loc) const
   {
-    ext = nullopt;
+    const target_type* tt (nullptr);
+    optional<string> ext;
+
     string& v (n.value);
 
     // If the target type is specified, resolve it and bail out if not found.
     // Otherwise, we know in the end it will resolve to something (if nothing
     // else, either dir{} or file{}), so we can go ahead and process the name.
     //
-    const target_type* r (nullptr);
     if (n.typed ())
     {
-      r = find_target_type (n.type);
+      tt = find_target_type (n.type);
 
-      if (r == nullptr)
-        return r;
+      if (tt == nullptr)
+        return make_pair (tt, move (ext));
     }
     else
     {
-      // Empty name as well as '.' and '..' signify a directory.
+      // Empty name as well as '.' and '..' signify a directory. Note that
+      // this logic must be consistent with other places (grep for "..").
       //
       if (v.empty () || v == "." || v == "..")
-        r = &dir::static_type;
+        tt = &dir::static_type;
     }
 
     // Directories require special name processing. If we find that more
-    // targets deviate, then we should make this target-type-specific.
+    // targets deviate, then we should make this target type-specific.
     //
-    if (r != nullptr && (r->is_a<dir> () || r->is_a<fsdir> ()))
+    if (tt != nullptr && (tt->is_a<dir> () || tt->is_a<fsdir> ()))
     {
       // The canonical representation of a directory name is with empty
       // value.
@@ -634,50 +636,43 @@ namespace build2
       // the extension (if any). We cannot assume the name part is a valid
       // filesystem name so we will have to do the splitting manually.
       //
-      path::size_type i (path::traits::rfind_separator (v));
+      // See also parser::expand_name_pattern() if changing anything here.
+      //
+      size_t p (path::traits::rfind_separator (v));
 
-      if (i != string::npos)
+      if (p != string::npos)
       {
         try
         {
-          n.dir /= dir_path (v, i != 0 ? i : 1); // Special case: "/".
+          n.dir /= dir_path (v, p != 0 ? p : 1); // Special case: "/".
         }
         catch (const invalid_path& e)
         {
           fail (loc) << "invalid path '" << e.path << "'";
         }
 
-        v = string (v, i + 1, string::npos);
+        v.erase (0, p + 1);
       }
 
-      // Extract the extension. Treat trailing dot as specified but empty
-      // extension.
+      // Extract the extension.
       //
-      string::size_type j (v.back () != '.'
-                           ? path::traits::find_extension (v)
-                           : v.size () - 1);
-
-      if (j != string::npos)
-      {
-        ext = string (v.c_str () + j + 1);
-        v.resize (j);
-      }
+      ext = target::split_name (v, loc);
     }
 
     // If the target type is still unknown, map it using the name/extension,
     // falling back to file{}.
     //
-    if (r == nullptr)
+    if (tt == nullptr)
     {
       // We only consider files without extension for file name mapping.
       //
       if (!ext)
-        r = find_file_target_type (this, v);
+        tt = find_file_target_type (this, v);
 
       //@@ TODO: derive type from extension.
 
-      if (r == nullptr)
-        r = &file::static_type;
+      if (tt == nullptr)
+        tt = &file::static_type;
     }
 
     // If the target type does not use extensions but one was specified,
@@ -685,15 +680,15 @@ namespace build2
     // diagnostics; see to_stream(target_key) for details).
     //
     if (ext                             &&
-        r->fixed_extension   == nullptr &&
-        r->default_extension == nullptr)
+        tt->fixed_extension   == nullptr &&
+        tt->default_extension == nullptr)
     {
       v += '.';
       v += *ext;
       ext = nullopt;
     }
 
-    return r;
+    return make_pair (tt, move (ext));
   }
 
   static target*
diff --git a/build2/scope.hxx b/build2/scope.hxx
index 73d95b6..d40d14a 100644
--- a/build2/scope.hxx
+++ b/build2/scope.hxx
@@ -213,12 +213,12 @@ namespace build2
 
     // Given a name, figure out its type, taking into account extensions,
     // special names (e.g., '.' and '..'), or anything else that might be
-    // relevant. Also process the name (in place) by extracting the
-    // extension, adjusting dir/value, etc., (note that the dir is not
+    // relevant. Process the name (in place) by extracting (and returning)
+    // extension, adjusting dir/leaf, etc., (note that the dir is not
     // necessarily normalized). Return NULL if not found.
     //
-    const target_type*
-    find_target_type (name&, optional<string>& ext, const location&) const;
+    pair<const target_type*, optional<string>>
+    find_target_type (name&, const location&) const;
 
     // Dynamically derive a new target type from an existing one. Return the
     // reference to the target type and an indicator of whether it was
diff --git a/build2/target-type.hxx b/build2/target-type.hxx
index 408a520..5027823 100644
--- a/build2/target-type.hxx
+++ b/build2/target-type.hxx
@@ -60,7 +60,11 @@ namespace build2
                                            const char*,
                                            bool search);
 
-    bool (*pattern) (const target_type&, const scope&, string&, bool reverse);
+    bool (*pattern) (const target_type&,
+                     const scope&,
+                     string& name,
+                     optional<string>& extension,
+                     bool reverse);
 
     void (*print) (ostream&, const target_key&);
 
diff --git a/build2/target.cxx b/build2/target.cxx
index e6188cd..ebc21db 100644
--- a/build2/target.cxx
+++ b/build2/target.cxx
@@ -192,6 +192,79 @@ namespace build2
     return r;
   }
 
+  optional<string> target::
+  split_name (string& v, const location& loc)
+  {
+    // We treat a single trailing dot as "specified no extension", double dots
+    // as a single trailing dot (that is, an escape sequence which can be
+    // repeated any number of times; in such cases we naturally assume there
+    // is no default extension) and triple dots as "unspecified (default)
+    // extension" (used when the extension in the name is not "ours", for
+    // example, cxx{foo.test...} for foo.test.cxx). An odd number of dots
+    // other than one or three is invalid.
+    //
+    optional<string> r;
+
+    size_t p;
+    if (v.back () != '.')
+    {
+      if ((p = path::traits::find_extension (v)) != string::npos)
+        r = string (v.c_str () + p + 1);
+    }
+    else
+    {
+      if ((p = v.find_last_not_of ('.')) == string::npos)
+        fail (loc) << "invalid target name '" << v << "'";
+
+      p++;                      // Position of the first trailing dot.
+      size_t n (v.size () - p); // Number of the trailing dots.
+
+      if (n == 1)
+        r = string ();
+      else if (n == 3)
+        ;
+      else if (n % 2 == 0)
+      {
+        p += n / 2; // Keep half of the dots.
+        r = string ();
+      }
+      else
+        fail (loc) << "invalid trailing dot sequence in target name '"
+                   << v << "'";
+    }
+
+    if (p != string::npos)
+      v.resize (p);
+
+    return r;
+  }
+
+  void target::
+  combine_name (string& v, const optional<string>& e)
+  {
+    if (v.back () == '.')
+    {
+      assert (e && e->empty ());
+
+      size_t p (v.find_last_not_of ('.'));
+      assert (p != string::npos);
+
+      p++;                      // Position of the first trailing dot.
+      size_t n (v.size () - p); // Number of the trailing dots.
+      v.append (n, '.');        // Double them.
+    }
+    else if (e)
+    {
+      v += '.';
+      v += *e;  // Empty or not.
+    }
+    else
+    {
+      if (path::traits::find_extension (v) != string::npos)
+        v += "...";
+    }
+  }
+
   // target_set
   //
   target_set targets;
@@ -802,7 +875,11 @@ namespace build2
   }
 
   static bool
-  dir_pattern (const target_type&, const scope&, string& v, bool r)
+  dir_pattern (const target_type&,
+               const scope&,
+               string& v,
+               optional<string>&,
+               bool r)
   {
     // Add/strip trailing directory separator unless already there.
     //
@@ -872,18 +949,20 @@ namespace build2
 
 #ifdef _WIN32
   static bool
-  exe_target_pattern (const target_type&, const scope&, string& v, bool r)
+  exe_target_pattern (const target_type&,
+                      const scope&,
+                      string& v,
+                      optional<string>& e,
+                      bool r)
   {
-    size_t p (path::traits::find_extension (v));
-
     if (r)
     {
-      assert (p != string::npos);
-      v.resize (p);
+      assert (e);
+      e = nullopt;
     }
-    else if (p == string::npos)
+    else if (!e)
     {
-      v += ".exe";
+      e = "exe";
       return true;
     }
 
@@ -921,18 +1000,17 @@ namespace build2
   buildfile_target_pattern (const target_type&,
                             const scope&,
                             string& v,
+                            optional<string>& e,
                             bool r)
   {
-    size_t p (path::traits::find_extension (v));
-
     if (r)
     {
-      assert (p != string::npos);
-      v.resize (p);
+      assert (e);
+      e = nullopt;
     }
-    else if (p == string::npos && v != "buildfile")
+    else if (!e && v != "buildfile")
     {
-      v += ".build";
+      e = "build";
       return true;
     }
 
@@ -1015,18 +1093,17 @@ namespace build2
   manifest_target_pattern (const target_type&,
                            const scope&,
                            string& v,
+                           optional<string>& e,
                            bool r)
   {
-    size_t p (path::traits::find_extension (v));
-
     if (r)
     {
-      assert (p != string::npos);
-      v.resize (p);
+      assert (e);
+      e = nullopt;
     }
-    else if (p == string::npos && v != "manifest")
+    else if (!e && v != "manifest")
     {
-      v += ".manifest";
+      e = "manifest";
       return true;
     }
 
diff --git a/build2/target.hxx b/build2/target.hxx
index db5de67..127940a 100644
--- a/build2/target.hxx
+++ b/build2/target.hxx
@@ -648,6 +648,18 @@ namespace build2
     static const target_type static_type;
 
   public:
+    // Split the name leaf into target name (in place) and extension
+    // (returned).
+    //
+    static optional<string>
+    split_name (string&, const location&);
+
+    // Combine the target name and extension into the name leaf.
+    //
+    static void
+    combine_name (string&, const optional<string>&);
+
+  public:
     virtual
     ~target ();
 
@@ -1704,7 +1716,9 @@ namespace build2
 
   template <const char* ext>
   bool
-  target_pattern_fix (const target_type&, const scope&, string&, bool);
+  target_pattern_fix (const target_type&, const scope&,
+                      string&, optional<string>&,
+                      bool);
 
   // Get the extension from the variable or use the default if none set. If
   // the default is NULL, then return NULL.
@@ -1715,7 +1729,9 @@ namespace build2
 
   template <const char* var, const char* def>
   bool
-  target_pattern_var (const target_type&, const scope&, string&, bool);
+  target_pattern_var (const target_type&, const scope&,
+                      string&, optional<string>&,
+                      bool);
 
   // Always return NULL extension.
   //
diff --git a/build2/target.txx b/build2/target.txx
index d832d6b..8030c1a 100644
--- a/build2/target.txx
+++ b/build2/target.txx
@@ -55,29 +55,27 @@ namespace build2
 
   template <const char* ext>
   bool
-  target_pattern_fix (const target_type&, const scope&, string& v, bool r)
+  target_pattern_fix (const target_type&,
+                      const scope&,
+                      string&,
+                      optional<string>& e,
+                      bool r)
   {
-    size_t p (path::traits::find_extension (v));
-
     if (r)
     {
       // If we get called to reverse then it means we've added the extension
-      // in the first place. So simply strip it.
+      // in the first place.
       //
-      assert (p != string::npos);
-      v.resize (p);
+      assert (e);
+      e = nullopt;
     }
     //
     // We only add our extension if there isn't one already.
     //
-    else if (p == string::npos)
+    else if (!e)
     {
-      if (*ext != '\0') // Don't add empty extension (means no extension).
-      {
-        v += '.';
-        v += ext;
-        return true;
-      }
+      e = ext;
+      return true;
     }
 
     return false;
@@ -115,35 +113,30 @@ namespace build2
 
   template <const char* var, const char* def>
   bool
-  target_pattern_var (const target_type& tt, const scope& s, string& v, bool r)
+  target_pattern_var (const target_type& tt,
+                      const scope& s,
+                      string&,
+                      optional<string>& e,
+                      bool r)
   {
-    size_t p (path::traits::find_extension (v));
-
     if (r)
     {
       // If we get called to reverse then it means we've added the extension
-      // in the first place. So simply strip it.
+      // in the first place.
       //
-      assert (p != string::npos);
-      v.resize (p);
+      assert (e);
+      e = nullopt;
     }
     //
     // We only add our extension if there isn't one already.
     //
-    else if (p == string::npos)
+    else if (!e)
     {
       // Use empty name as a target since we only want target type/pattern-
       // specific variables that match any target (e.g., '*' but not '*.txt').
       //
-      if (auto e = target_extension_var_impl (tt, string (), s, var, def))
-      {
-        if (!e->empty ()) // Don't add empty extension (means no extension).
-        {
-          v += '.';
-          v += *e;
-          return true;
-        }
-      }
+      if ((e = target_extension_var_impl (tt, string (), s, var, def)))
+        return true;
     }
 
     return false;
diff --git a/build2/test/target.cxx b/build2/test/target.cxx
index a517240..57e2cb5 100644
--- a/build2/test/target.cxx
+++ b/build2/test/target.cxx
@@ -24,18 +24,17 @@ namespace build2
     testscript_target_pattern (const target_type&,
                                const scope&,
                                string& v,
+                               optional<string>& e,
                                bool r)
     {
-      size_t p (path::traits::find_extension (v));
-
       if (r)
       {
-        assert (p != string::npos);
-        v.resize (p);
+        assert (e);
+        e = nullopt;
       }
-      else if (p == string::npos && v != "testscript")
+      else if (!e && v != "testscript")
       {
-        v += ".test";
+        e = "test";
         return true;
       }
 
diff --git a/tests/name/extension.test b/tests/name/extension.test
new file mode 100644
index 0000000..e97d0ab
--- /dev/null
+++ b/tests/name/extension.test
@@ -0,0 +1,48 @@
+# file      : tests/name/extension.test
+# copyright : Copyright (c) 2014-2018 Code Synthesis Ltd
+# license   : MIT; see accompanying LICENSE file
+
+test.arguments = --match-only update
+
+.include ../common.test
+
++cat <<EOI >=build/root.build
+define txt: file
+txt{*}: extension = txt
+EOI
+
+: unspecified
+:
+touch foo.txt;
+$* <'./: txt{foo}'
+
+: specified
+:
+touch foo.text;
+$* <'./: txt{foo.text}'
+
+: specified-none
+:
+touch foo;
+$* <'./: txt{foo.}'
+
+: specified-default
+:
+touch foo.test.txt;
+$* <'./: txt{foo.test...}'
+
+: specified-escape-one
+:
+touch foo.;
+$* <'./: txt{foo..}'
+
+: specified-escape-two
+:
+touch foo..;
+$* <'./: txt{foo....}'
+
+: specified-invalid
+:
+$* <'./: txt{foo.....}' 2>>EOE != 0
+<stdin>:1:5: error: invalid trailing dot sequence in target name 'foo.....'
+EOE