From 83459829f24624e3cee20a7199af5c69e9678b69 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 19 Oct 2018 10:44:52 +0200
Subject: Suggest override variable (config.x) when tool is not found

---
 build2/bin/guess.cxx | 47 +++++++++++++++++++++++++++++++++++++++++------
 build2/cc/guess.cxx  | 21 ++++++++++++++++-----
 build2/cc/guess.hxx  |  1 +
 build2/cc/module.cxx |  1 +
 build2/cli/init.cxx  |  6 ++++--
 5 files changed, 63 insertions(+), 13 deletions(-)

diff --git a/build2/bin/guess.cxx b/build2/bin/guess.cxx
index a142e59..78a1940 100644
--- a/build2/bin/guess.cxx
+++ b/build2/bin/guess.cxx
@@ -42,12 +42,29 @@ namespace build2
     {
       tracer trace ("bin::guess_ar");
 
+      process_path arp, rlp;
       guess_result arr, rlr;
 
-      process_path arp (run_search (ar, true, fallback));
-      process_path rlp (rl != nullptr
-                        ? run_search (*rl, true, fallback)
-                        : process_path ());
+      {
+        auto df = make_diag_frame (
+          [](const diag_record& dr)
+          {
+            dr << info << "use config.bin.ar to override";
+          });
+
+        arp = run_search (ar, true, fallback);
+      }
+
+      if (rl != nullptr)
+      {
+        auto df = make_diag_frame (
+          [](const diag_record& dr)
+          {
+            dr << info << "use config.bin.ranlib to override";
+          });
+
+        rlp = run_search (*rl, true, fallback);
+      }
 
       // Binutils, LLVM, and FreeBSD ar/ranlib all recognize the --version
       // option. While Microsoft's lib.exe doesn't support --version, it only
@@ -244,7 +261,16 @@ namespace build2
 
       guess_result r;
 
-      process_path pp (run_search (ld, true, fallback));
+      process_path pp;
+      {
+        auto df = make_diag_frame (
+          [](const diag_record& dr)
+          {
+            dr << info << "use config.bin.ld to override";
+          });
+
+        pp = run_search (ld, true, fallback);
+      }
 
       // Binutils ld recognizes the --version option. Microsoft's link.exe
       // doesn't support --version (nor any other way to get the version
@@ -363,7 +389,16 @@ namespace build2
 
       guess_result r;
 
-      process_path pp (run_search (rc, true, fallback));
+      process_path pp;
+      {
+        auto df = make_diag_frame (
+          [](const diag_record& dr)
+          {
+            dr << info << "use config.bin.rc to override";
+          });
+
+        pp = run_search (rc, true, fallback);
+      }
 
       // Binutils windres recognizes the --version option.
       //
diff --git a/build2/cc/guess.cxx b/build2/cc/guess.cxx
index e9f85e3..e75a6ee 100644
--- a/build2/cc/guess.cxx
+++ b/build2/cc/guess.cxx
@@ -288,13 +288,22 @@ namespace build2
     // Allowed to change pre if succeeds.
     //
     static guess_result
-    guess (lang, const path& xc, string& pre)
+    guess (lang, const string& xv, const path& xc, string& pre)
     {
       tracer trace ("cc::guess");
 
       guess_result r;
 
-      process_path xp (run_search (xc, false /* init */)); // Note: cached.
+      process_path xp;
+      {
+        auto df = make_diag_frame (
+          [&xv](const diag_record& dr)
+          {
+            dr << info << "use " << xv << " to override";
+          });
+
+        xp = run_search (xc, false /* init */); // Note: cached.
+      }
 
       // Start with -v. This will cover gcc and clang.
       //
@@ -1450,6 +1459,7 @@ namespace build2
 
     const compiler_info&
     guess (lang xl,
+           const string& xv,
            const path& xc,
            const strings* c_po, const strings* x_po,
            const strings* c_co, const strings* x_co,
@@ -1485,16 +1495,17 @@ namespace build2
 
       if (!type.empty ())
       {
-        gr = guess (xl, xc, type);
+        gr = guess (xl, xv, xc, type);
 
         if (gr.empty ())
-          warn << xc << " name looks like " << type << " but it is not";
+          warn << xc << " looks like " << type << " but it is not" <<
+            info << "use " << xv << " to override";
 
         type.clear ();
       }
 
       if (gr.empty ())
-        gr = guess (xl, xc, type);
+        gr = guess (xl, xv, xc, type);
 
       if (gr.empty ())
         fail << "unable to guess " << xl << " compiler type of " << xc;
diff --git a/build2/cc/guess.hxx b/build2/cc/guess.hxx
index 599c56d..6e0281c 100644
--- a/build2/cc/guess.hxx
+++ b/build2/cc/guess.hxx
@@ -215,6 +215,7 @@ namespace build2
     //
     const compiler_info&
     guess (lang,
+           const string& xv, // Override variable (config.x) for diagnostics.
            const path& xc,
            const strings* c_poptions, const strings* x_poptions,
            const strings* c_coptions, const strings* x_coptions,
diff --git a/build2/cc/module.cxx b/build2/cc/module.cxx
index e9d5c09..76935f9 100644
--- a/build2/cc/module.cxx
+++ b/build2/cc/module.cxx
@@ -117,6 +117,7 @@ namespace build2
       //
       const path& xc (cast<path> (*p.first));
       ci_ = &build2::cc::guess (x_lang,
+                                config_x.name,
                                 xc,
                                 cast_null<strings> (rs[config_c_poptions]),
                                 cast_null<strings> (rs[config_x_poptions]),
diff --git a/build2/cli/init.cxx b/build2/cli/init.cxx
index 4ad8a1a..bad2533 100644
--- a/build2/cli/init.cxx
+++ b/build2/cli/init.cxx
@@ -150,7 +150,8 @@ namespace build2
               else
               {
                 if (!optional)
-                  fail << cli << " is not command line interface compiler";
+                  fail << cli << " is not command line interface compiler" <<
+                    info << "use config.cli to override";
 
                 v.clear ();
               }
@@ -178,7 +179,8 @@ namespace build2
             // found). So it would be good to redirect child's STDERR.
             //
             if (!optional)
-              error << "unable to execute " << args[0] << ": " << e;
+              error << "unable to execute " << args[0] << ": " << e <<
+                info << "use config.cli to override";
 
             if (e.child)
               exit (1);
-- 
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