Add and use libclang_error exception class

include/cppast/libclang_parser.hpp

@@ -5,6 +5,8 @@
 #ifndef CPPAST_LIBCLANG_PARSER_HPP_INCLUDED
 #define CPPAST_LIBCLANG_PARSER_HPP_INCLUDED
 
+#include <stdexcept>
+
 #include <cppast/parser.hpp>
 
 namespace cppast
@@ -53,6 +55,16 @@ namespace cppast
         friend detail::libclang_compile_config_access;
     };
 
+    /// The exception thrown when a fatal parse error occurs.
+    class libclang_error final : public std::runtime_error
+    {
+    public:
+        /// \effects Creates it with a message.
+        libclang_error(std::string msg) : std::runtime_error(std::move(msg))
+        {
+        }
+    };
+
     /// A parser that uses libclang.
     class libclang_parser final : public parser
     {

src/libclang/libclang_parser.cpp

@@ -134,7 +134,23 @@ namespace
                                             | CXTranslationUnit_KeepGoing, // flags
                                         &tu);
         if (error != CXError_Success)
-            DEBUG_UNREACHABLE(detail::assert_handler{}, "libclang error"); // TODO
+        {
+            switch (error)
+            {
+            case CXError_Success:
+                DEBUG_UNREACHABLE(detail::assert_handler{});
+                break;
+
+            case CXError_Failure:
+                throw libclang_error("clang_parseTranslationUnit: generic error");
+            case CXError_Crashed:
+                throw libclang_error("clang_parseTranslationUnit: libclang crashed :(");
+            case CXError_InvalidArguments:
+                throw libclang_error("clang_parseTranslationUnit: you shouldn't see this message");
+            case CXError_ASTReadError:
+                throw libclang_error("clang_parseTranslationUnit: AST deserialization error");
+            }
+        }
 
         return tu;
     }

src/libclang/preprocessor.cpp

@@ -73,7 +73,9 @@ namespace
 
         auto exit_code = process.get_exit_status();
         if (exit_code != 0)
-            DEBUG_UNREACHABLE(detail::assert_handler{}); // TODO: improve error handling
+            throw libclang_error("preprocessor: command '" + cmd
+                                 + "' exited with non-zero exit code (" + std::to_string(exit_code)
+                                 + ")");
 
         return preprocessed;
     }