Early error if toolchain unavailable for testsuite (#1655)

testsuite/run.py

@@ -10,6 +10,7 @@
 from __future__ import absolute_import, print_function
 
 import os.path
+import shutil
 import sys
 from argparse import ArgumentTypeError
 
@@ -35,6 +36,13 @@ def add_options(self, parser):
             dest='alr_path', metavar='FILE', help='''Set `alr` binary to run the testsuite
             against. Defaults to `alr` from project's `bin` directory.''')
 
+    def require_executable(self, name):
+        path = shutil.which(name)
+        if path is None:
+            raise FileNotFoundError(f"{name} not found in PATH")
+        else:
+            print(f"Using {name} at {path}")
+
     def set_up(self):
         super().set_up()
         os.environ['ALR_PATH'] = self.main.args.alr_path
@@ -51,6 +59,13 @@ def set_up(self):
         # during the tests (e.g. submitting a release by accident)
         os.environ["ALR_TESTSUITE"] = "TRUE"
 
+        # Ensure toolchain is in scope, or err early instead of during tests
+        # Locate gnat and gprbuild in path and report their location
+        required_executables = ['gnat', 'gprbuild']
+        for exe in required_executables:
+            self.require_executable(exe)
+        print()
+
     def _alr_path(self, alr_file):
         alr_path = os.path.abspath(alr_file)
         if not os.path.isfile(alr_path):