Implement searching for b in bpkg's exec directory as last resort

This way if we run /opt/build2/bin/bpkg it will be able to find b in
/opt/build2/bin/ without PATH.

3 files changed, 31 insertions, 8 deletions

diff --git a/bpkg/bpkg.cxx b/bpkg/bpkg.cxx
index 561e32e..d6f6924 100644
--- a/bpkg/bpkg.cxx
+++ b/bpkg/bpkg.cxx
@@ -98,6 +98,8 @@ try
 {
   using namespace cli;
 
+  exec_dir = path (argv[0]).directory ();
+
   argv_file_scanner scan (argc, argv, "--options-file");
 
   // First parse common options and --version/--help.
diff --git a/bpkg/utility b/bpkg/utility
index 85cf1ca..a09cac5 100644
--- a/bpkg/utility
+++ b/bpkg/utility
@@ -78,11 +78,22 @@ namespace bpkg
   // The process command line is printed for verbosity >= 2 (essential
   // command lines).
   //
+  // If fallback is specified, then this directory is searched for the
+  // executable as a last resort.
+  //
   void
-  run (const char* args[]);
+  run (const char* args[], const dir_path& fallback = dir_path ());
 
   inline void
-  run (cstrings& args) {run (args.data ());}
+  run (cstrings& args, const dir_path& fallback = dir_path ())
+  {
+    run (args.data (), fallback);
+  }
+
+  // Directory extracted from argv[0] (i.e., this process' recall directory)
+  // or empty if there is none. Can be used as a search fallback.
+  //
+  extern dir_path exec_dir;
 
   // Run build2, mapping verbosity levels. If quiet is true, then run build2
   // quiet if our verbosity level is 1. Common vars (cvars) are set on the
diff --git a/bpkg/utility.cxx b/bpkg/utility.cxx
index 12ef220..002d316 100644
--- a/bpkg/utility.cxx
+++ b/bpkg/utility.cxx
@@ -167,15 +167,19 @@ namespace bpkg
     }
   }
 
+  dir_path exec_dir;
+
   void
-  run (const char* args[])
+  run (const char* args[], const dir_path& fallback)
   {
-    if (verb >= 2)
-      print_process (args);
-
     try
     {
-      process pr (args);
+      process_path pp (process::path_search (args[0], fallback));
+
+      if (verb >= 2)
+        print_process (args);
+
+      process pr (pp, args);
 
       if (!pr.wait ())
         throw failed (); // Assume the child issued diagnostics.
@@ -253,7 +257,13 @@ namespace bpkg
     args.push_back (bspec.c_str ());
 
     args.push_back (nullptr);
-    run (args);
+
+    // Use our executable directory as a fallback search since normally the
+    // entire toolchain is installed into one directory. This way, for
+    // example, if we installed into /opt/build2 and run bpkg with absolute
+    // path (and without PATH), then bpkg will be able to find "its" b.
+    //
+    run (args, exec_dir);
   }
 
   bool exception_unwinding_dtor = false;