From f0da422177d416aef2e446b23e8bbf2ec79a9aab Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 3 May 2019 14:11:17 +0200
Subject: Support <>-style header specification in importable_headers

---
 build2/cc/compile-rule.cxx |  8 +++++++-
 build2/cc/module.cxx       | 50 +++++++++++++++++++++++++++++++++++++++-------
 build2/cxx/init.cxx        |  6 +++---
 3 files changed, 53 insertions(+), 11 deletions(-)

diff --git a/build2/cc/compile-rule.cxx b/build2/cc/compile-rule.cxx
index dd38945..794b64e 100644
--- a/build2/cc/compile-rule.cxx
+++ b/build2/cc/compile-rule.cxx
@@ -2005,7 +2005,13 @@ namespace build2
             //
             if (const strings* ih = import_hdr)
             {
-              auto i (lower_bound (ih->begin (), ih->end (), hp));
+              auto i (lower_bound (ih->begin (),
+                                   ih->end (),
+                                   hp,
+                                   [] (const string& x, const string& y)
+                                   {
+                                     return path::traits::compare (x, y) < 0;
+                                   }));
 
               if (i != ih->end () && *i == hp)
               {
diff --git a/build2/cc/module.cxx b/build2/cc/module.cxx
index 20e39a8..1e3806a 100644
--- a/build2/cc/module.cxx
+++ b/build2/cc/module.cxx
@@ -290,8 +290,8 @@ namespace build2
       //
       tstd = translate_std (ci, rs, cast_null<string> (rs[x_std]));
 
-      // Extract system library search paths from the compiler and determine
-      // additional system include search paths.
+      // Extract system header/library search paths from the compiler and
+      // determine if we need any additional search paths.
       //
       dir_paths lib_dirs;
       dir_paths inc_dirs;
@@ -506,17 +506,53 @@ namespace build2
       // Process, sort, and cache (in this->import_hdr) importable headers.
       // Keep the cache NULL if unused or empty.
       //
-      // @@ MODHDR TODO: translate <> to absolute paths.
       // @@ MODHDR TODO: support exclusions entries (e.g., -<stdio.h>)?
       //
       if (modules && x_importable_headers != nullptr)
       {
-        strings* v (cast_null<strings> (rs.assign (x_importable_headers)));
+        strings* ih (cast_null<strings> (rs.assign (x_importable_headers)));
 
-        if (v != nullptr && !v->empty ())
+        if (ih != nullptr && !ih->empty ())
         {
-          sort (v->begin (), v->end ());
-          import_hdr = v;
+          // Translate <>-style header names to absolute paths using the
+          // compiler's include search paths.
+          //
+          for (string& h: *ih)
+          {
+            if (h.empty () || h.front () != '<' || h.back () != '>')
+              continue;
+
+            h.pop_back ();
+            h.erase (0, 1);
+
+            path f; // Reuse the buffer.
+            bool r (false);
+            for (const dir_path& d: sys_inc_dirs)
+            {
+              if ((r = file_exists ((f = d, f /= h),
+                                    true /* follow_symlinks */,
+                                    true /* ignore_errors */)))
+              {
+                h = move (f.normalize ()).string ();
+                break;
+              }
+            }
+
+            // What should we do if not found? While we can fail, this could
+            // be too drastic if, for example, the header is "optional" and
+            // may or may not be present/used. So for now let's restore the
+            // original form to aid debugging (it can't possibly match any
+            // absolute path).
+            //
+            if (!r)
+            {
+              h.insert (0, 1, '<');
+              h.push_back ('>');
+            }
+          }
+
+          sort (ih->begin (), ih->end ());
+          import_hdr = ih;
         }
       }
 
diff --git a/build2/cxx/init.cxx b/build2/cxx/init.cxx
index a04a30a..2491d90 100644
--- a/build2/cxx/init.cxx
+++ b/build2/cxx/init.cxx
@@ -399,9 +399,9 @@ namespace build2
         //
         // A header can be specified either as an absolute and normalized path
         // or as a <>-style include name. The latter kind is automatically
-        // translated to the absolute form based on the include search paths
-        // extracted from the compiler. Note also that all entries must be
-        // specified before loading the cxx module.
+        // translated to the absolute form based on the compiler's system
+        // header search paths (as opposed to -I). Note also that all entries
+        // must be specified before loading the cxx module.
         //
         &v.insert<strings> ("config.cxx.importable_headers", true),
 
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