Improve reporting when bootstrapping from source

Signed-off-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

lib/spack/llnl/util/lang.py

@@ -996,11 +996,8 @@ def _receive_forwarded(self, context: str, exc: Exception, tb: List[str]):
     def grouped_message(self, with_tracebacks: bool = True) -> str:
         """Print out an error message coalescing all the forwarded errors."""
         each_exception_message = [
-            "{0} raised {1}: {2}{3}".format(
-                context,
-                exc.__class__.__name__,
-                exc,
-                "\n{0}".format("".join(tb)) if with_tracebacks else "",
+            "\n\t{0} raised {1}: {2}\n{3}".format(
+                context, exc.__class__.__name__, exc, f"\n{''.join(tb)}" if with_tracebacks else ""
             )
             for context, exc, tb in self.exceptions
         ]

lib/spack/spack/bootstrap/clingo.py

@@ -62,9 +62,15 @@ def _valid_compiler_or_raise(self):
             )
         candidates.sort(key=lambda x: x.version, reverse=True)
         best = candidates[0]
-        # FIXME (compiler as nodes): we need to find a better place for setting namespaces
+        # Get compilers for bootstrapping from the 'builtin' repository
         best.namespace = "builtin"
-        # TODO: check it has C and C++, and supports C++14
+        # If the compiler does not support C++ 14, fail with a legible error message
+        try:
+            _ = best.package.standard_flag(language="cxx", standard="14")
+        except RuntimeError as e:
+            raise RuntimeError(
+                "cannot find a compiler supporting C++ 14 [needed to bootstrap clingo]"
+            ) from e
         return candidates[0]
 
     def _externals_from_yaml(

lib/spack/spack/spec.py

@@ -5221,9 +5221,6 @@ class DuplicateCompilerSpecError(spack.error.SpecError):
 class UnsupportedCompilerError(spack.error.SpecError):
     """Raised when the user asks for a compiler spack doesn't know about."""
 
-    def __init__(self, compiler_name):
-        super().__init__("The '%s' compiler is not yet supported." % compiler_name)
-
 
 class DuplicateArchitectureError(spack.error.SpecError):
     """Raised when the same architecture occurs in a spec twice."""