From becea217436a79b7ef37a023da6cb4c560225a71 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 2 Dec 2015 14:24:10 +0200
Subject: Redo extension derivation for file{}, doc{}, and cli{}

We now first check the 'extension' variable, then use the default.
---
 build/cli/target.cxx |  6 ++++--
 build/cxx/target.cxx | 12 ++++++------
 build/parser.cxx     |  7 +++++++
 build/target         |  5 +++--
 build/target.cxx     |  9 +++++----
 build/target.txx     | 22 ++++++++++++++--------
 6 files changed, 39 insertions(+), 22 deletions(-)

diff --git a/build/cli/target.cxx b/build/cli/target.cxx
index a480633..6eef99b 100644
--- a/build/cli/target.cxx
+++ b/build/cli/target.cxx
@@ -15,13 +15,15 @@ namespace build
   {
     // cli
     //
-    constexpr const char cli_ext[] = "cli";
+    constexpr const char cli_ext_var[] = "extension";
+    constexpr const char cli_ext_def[] = "cli";
+
     const target_type cli::static_type
     {
       "cli",
       &file::static_type,
       &target_factory<cli>,
-      &target_extension_fix<cli_ext>,
+      &target_extension_var<cli_ext_var, cli_ext_def>,
       &search_file,
       false
     };
diff --git a/build/cxx/target.cxx b/build/cxx/target.cxx
index c8680b7..b84167b 100644
--- a/build/cxx/target.cxx
+++ b/build/cxx/target.cxx
@@ -16,7 +16,7 @@ namespace build
       "hxx",
       &file::static_type,
       &target_factory<hxx>,
-      &target_extension_var<hxx_ext_var>,
+      &target_extension_var<hxx_ext_var, nullptr>,
       &search_file,
       false
     };
@@ -27,7 +27,7 @@ namespace build
       "ixx",
       &file::static_type,
       &target_factory<ixx>,
-      &target_extension_var<ixx_ext_var>,
+      &target_extension_var<ixx_ext_var, nullptr>,
       &search_file,
       false
     };
@@ -38,7 +38,7 @@ namespace build
       "txx",
       &file::static_type,
       &target_factory<txx>,
-      &target_extension_var<txx_ext_var>,
+      &target_extension_var<txx_ext_var, nullptr>,
       &search_file,
       false
     };
@@ -49,7 +49,7 @@ namespace build
       "cxx",
       &file::static_type,
       &target_factory<cxx>,
-      &target_extension_var<cxx_ext_var>,
+      &target_extension_var<cxx_ext_var, nullptr>,
       &search_file,
       false
     };
@@ -60,7 +60,7 @@ namespace build
       "h",
       &file::static_type,
       &target_factory<h>,
-      &target_extension_var<h_ext_var>,
+      &target_extension_var<h_ext_var, nullptr>,
       &search_file,
       false
     };
@@ -71,7 +71,7 @@ namespace build
       "c",
       &file::static_type,
       &target_factory<c>,
-      &target_extension_var<c_ext_var>,
+      &target_extension_var<c_ext_var, nullptr>,
       &search_file,
       false
     };
diff --git a/build/parser.cxx b/build/parser.cxx
index c896c71..ee22254 100644
--- a/build/parser.cxx
+++ b/build/parser.cxx
@@ -818,6 +818,8 @@ namespace build
     return r;
   }
 
+  constexpr const char derived_ext_var[] = "extension";
+
   void parser::
   define (token& t, token_type& tt)
   {
@@ -852,6 +854,11 @@ namespace build
       dt->base = bt;
       dt->factory = &derived_factory;
 
+      // Override extension derivation function: we most likely don't want
+      // to use the same default as our base (think cli: file).
+      //
+      dt->extension = &target_extension_var<derived_ext_var, nullptr>;
+
       target_type& rdt (*dt); // Save a non-const reference to the object.
 
       auto pr (scope_->target_types.emplace (dn, target_type_ref (move (dt))));
diff --git a/build/target b/build/target
index 2aea7ae..69f8f4f 100644
--- a/build/target
+++ b/build/target
@@ -1051,9 +1051,10 @@ namespace build
   const std::string&
   target_extension_fix (const target_key&, scope&);
 
-  // Get the extension from the variable.
+  // Get the extension from the variable or use the default if none set.
+  // Issue diagnostics and fail if the default is NULL.
   //
-  template <const char* var>
+  template <const char* var, const char* def>
   const std::string&
   target_extension_var (const target_key&, scope&);
 
diff --git a/build/target.cxx b/build/target.cxx
index 5c31311..41fe54a 100644
--- a/build/target.cxx
+++ b/build/target.cxx
@@ -433,13 +433,15 @@ namespace build
                   (e != nullptr ? e : &extension_pool.find ("")));
   }
 
-  constexpr const char extension_var[] = "extension";
+  constexpr const char file_ext_var[] = "extension";
+  constexpr const char file_ext_def[] = "";
+
   const target_type file::static_type
   {
     "file",
     &path_target::static_type,
     &file_factory<file>,
-    &target_extension_var<extension_var>,
+    &target_extension_var<file_ext_var, file_ext_def>,
     &search_file,
     false
   };
@@ -493,13 +495,12 @@ namespace build
     false
   };
 
-  constexpr const char doc_ext[] = "";
   const target_type doc::static_type
   {
     "doc",
     &file::static_type,
     &file_factory<doc>,
-    &target_extension_fix<doc_ext>,
+    &target_extension_var<file_ext_var, file_ext_def>, // Same as file.
     &search_file,
     false
   };
diff --git a/build/target.txx b/build/target.txx
index e347f77..89a402e 100644
--- a/build/target.txx
+++ b/build/target.txx
@@ -10,24 +10,27 @@
 namespace build
 {
   template <const char* ext>
-  const std::string&
+  const string&
   target_extension_fix (const target_key&, scope&)
   {
     return extension_pool.find (ext);
   }
 
-  template <const char* var>
-  const std::string&
+  template <const char* var, const char* def>
+  const string&
   target_extension_var (const target_key& tk, scope& s)
   {
     // Include target type/pattern-specific variables.
     //
-    auto l (s.lookup (tk, var));
+    if (auto l = s.lookup (tk, var))
+      return extension_pool.find (as<string> (*l));
+
+    if (def != nullptr)
+      return extension_pool.find (def);
 
-    if (!l)
     {
       diag_record dr;
-      dr << fail << "no default extension in variable '" << var << "'"
+      dr << error << "no default extension in variable '" << var << "'"
          << info << "required to derive file name for ";
 
       // This is a bit hacky: we may be dealing with a target (see
@@ -39,11 +42,14 @@ namespace build
         dr << "target " << tk;
       else
       {
-        const std::string* proj (nullptr); // Used for local prerequisites.
+        const string* proj (nullptr); // Used for local prerequisites.
         dr << "prerequisite " << prerequisite_key {&proj, tk, &s};
       }
+
+      dr << info << "perhaps you forgot to add "
+         << tk.type->name << "{*}: " << var << " = ...";
     }
 
-    return extension_pool.find (as<std::string> (*l));
+    throw failed ();
   }
 }
-- 
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