C import: unions (SDL_Event) and their fields; #defines that are expressions, casts or text; typedef'd structs no function mentions; FLAG_A | FLAG_B fits a u64

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/new/c_unions_macros.fch

@@ -0,0 +1,25 @@
+// C unions (SDL_Event-style) and #defines that are expressions, strings or casts
+import "cunion.h"
+link "cunion.c"
+
+fn main() {
+    print(EV_MOTION, EV_KEY, FLAG_BIG, FLAGS_BOTH, HALF, GREETING, LONG_NAME)
+    u64 flags = FLAG_BIG | FLAG_GL
+    u32 small = EV_KEY
+    print(flags, small)
+
+    Event e
+    if poll_event(addr(e)) != 0 && e.type == EV_MOTION {
+        print("motion", e.motion.x, e.motion.y)
+    }
+    k := Event(key: Key(type: EV_KEY, key: 32))
+    print(k.type == EV_KEY, k.key.key)
+    []Event queue
+    queue.push(e)
+    queue.push(k)
+    print(queue[1].key.key, queue.len)
+
+    Tagged t
+    t.as.f = 0.5
+    print(t.as.f)
+}

tests/new/c_unions_macros.out

@@ -0,0 +1,6 @@
+1024 1025 1099511627776 1099511627778 0.5 hi	there ab
+1099511627778 1025
+motion 1.5 -2
+true 32
+32 2
+0.5

tests/new/cunion.c

@@ -0,0 +1,7 @@
+#include "cunion.h"
+int poll_event(Event *e) {
+    e->motion.type = EV_MOTION;
+    e->motion.x = 1.5f;
+    e->motion.y = -2.0f;
+    return 1;
+}

tests/new/cunion.h

@@ -0,0 +1,30 @@
+// C unions and #define constants that are expressions (tests/new/c_unions_macros.fch)
+#include <stdint.h>
+
+typedef struct { uint32_t type; float x, y; } Motion;
+typedef struct { uint32_t type; int32_t key; } Key;
+typedef union {
+    uint32_t type;
+    Motion motion;
+    Key key;
+    uint8_t padding[64];
+} Event;
+
+typedef struct { int kind; union { int i; float f; } as; } Tagged;
+
+#define EV_MOTION 0x400u
+#define EV_KEY (EV_MOTION + 1)
+#define FLAG_BIG ((uint64_t)1 << 40)
+#define FLAG_GL 0x2ULL
+#define FLAGS_BOTH (FLAG_BIG | FLAG_GL)
+#define HALF (1.0 / 2)
+#define GREETING "hi\tthere"
+#define LONG_NAME "a" "b"
+#define NOT_A_CONSTANT do { } while (0)
+
+static inline int fill_key(Event *e, int key) {
+    e->key.type = EV_KEY;
+    e->key.key = key;
+    return 1;
+}
+int poll_event(Event *e);

tests/new/fail/union_two_fields.fch

@@ -0,0 +1,5 @@
+// expect: Event is a C union: give one field by name
+import "../cunion.h"
+fn main() {
+    e := Event(1, 2)
+}