stage1: make C++ switch fallthrough an error

Make fallthrough an error when compiler supports it. This requires a new
macro that is defined with such compilers to be used as a statement, at
all fallthrough sites:

    switch (...) {
        case 0:
            ...
            ZIG_FALLTHROUGH;
        case 1:
            ...
            break;
        default:
            ...
            break;
    }

If we ever move to C++17 as minimal requirement, then the macro can be
replaced with `[[fallthrough]];` at statement sites.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/dump_analysis.cpp b/src/dump_analysis.cpp
index c31438b658..3522dcf6f4 100644
--- a/src/dump_analysis.cpp
+++ b/src/dump_analysis.cpp
@@ -80,7 +80,7 @@ static void jw_array_elem(JsonWriter *jw) {
             zig_unreachable();
         case JsonWriterStateArray:
             fprintf(jw->f, ",");
-            // fallthrough
+            ZIG_FALLTHROUGH;
         case JsonWriterStateArrayStart:
             jw->state[jw->state_index] = JsonWriterStateArray;
             jw_push_state(jw, JsonWriterStateValue);
@@ -134,7 +134,7 @@ static void jw_object_field(JsonWriter *jw, const char *name) {
             zig_unreachable();
         case JsonWriterStateObject:
             fprintf(jw->f, ",");
-            // fallthrough
+            ZIG_FALLTHROUGH;
         case JsonWriterStateObjectStart:
             jw->state[jw->state_index] = JsonWriterStateObject;
             jw_push_state(jw, JsonWriterStateValue);