feat(codegen): accept pointers to C-struct records in EXTERN signatures

A TYPE record whose fields are all C types, C structs or pointer types to
C structs now crosses the EXTERN "C" boundary through a pointer type.
Records by value are rejected for now, and a pointer to a record with a
non-C field names that field.

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

8 files changed, 79 insertions, 0 deletions

diff --git a/tests/i/extern-c-struct/case.json b/tests/i/extern-c-struct/case.json
new file mode 100644
index 0000000..1ce5970
--- /dev/null
+++ b/tests/i/extern-c-struct/case.json
@@ -0,0 +1,5 @@
+{
+  "objects": [
+    {"source": "lib.c", "output": "lib.o"}
+  ]
+}
diff --git a/tests/i/extern-c-struct/expected.txt b/tests/i/extern-c-struct/expected.txt
new file mode 100644
index 0000000..62e50ed
--- /dev/null
+++ b/tests/i/extern-c-struct/expected.txt
@@ -0,0 +1,3 @@
+S 4.500000 5
+G 0.500000 7
+9
diff --git a/tests/i/extern-c-struct/lib.c b/tests/i/extern-c-struct/lib.c
new file mode 100644
index 0000000..39380ec
--- /dev/null
+++ b/tests/i/extern-c-struct/lib.c
@@ -0,0 +1,11 @@
+struct Sample {
+    char tag;
+    double value;
+    int count;
+};
+
+static struct Sample shared = {'G', 0.5, 7};
+
+void scale_sample(struct Sample *s, int k) { s->value *= k; }
+struct Sample *shared_sample(void) { return &shared; }
+int shared_count(void) { return shared.count; }
diff --git a/tests/i/extern-c-struct/notes.md b/tests/i/extern-c-struct/notes.md
new file mode 100644
index 0000000..1a0d215
--- /dev/null
+++ b/tests/i/extern-c-struct/notes.md
@@ -0,0 +1,7 @@
+# extern-c-struct
+
+Human review: pending. Expected output was independently traced by AI, not captured from cpsc.
+
+Basis: compiler extension (EXTERN "C", INCLUDE_OBJ of a user object); a record whose fields are all C types has the layout of the matching C struct.
+
+Trace: the harness compiles `lib.c` with the host C compiler. Sample matches `struct Sample {char; double; int}`, including the padding after the char. S is 'S', 1.5, 5. scale_sample(^S, 3) multiplies the value through the pointer to 4.5 and leaves tag and count alone, so the first line is `S 4.500000 5`. shared_sample returns the address of the static struct in lib.c, initialised to 'G', 0.5, 7, giving `G 0.500000 7`. P^.Count <- 9 writes through that pointer into the C object, so shared_count() returns 9.
diff --git a/tests/i/extern-c-struct/program.cps b/tests/i/extern-c-struct/program.cps
new file mode 100644
index 0000000..1954d29
--- /dev/null
+++ b/tests/i/extern-c-struct/program.cps
@@ -0,0 +1,22 @@
+// Records whose fields are C types pass to C functions through pointer types.
+INCLUDE_OBJ "lib.o"
+TYPE Sample
+    DECLARE Tag : C_CHAR
+    DECLARE Value : C_DOUBLE
+    DECLARE Count : C_INT
+ENDTYPE
+TYPE PSample = ^Sample
+EXTERN "C" EXTERN_PROCEDURE scale_sample(PSample, C_INT)
+EXTERN "C" EXTERN_FUNCTION shared_sample() RETURNS PSample
+EXTERN "C" EXTERN_FUNCTION shared_count() RETURNS C_INT
+DECLARE S : Sample
+DECLARE P : PSample
+S.Tag <- (C_CHAR)'S'
+S.Value <- (C_DOUBLE)1.5
+S.Count <- (C_INT)5
+CALL scale_sample(^S, (C_INT)3)
+OUTPUT S.Tag, " ", S.Value, " ", S.Count
+P <- shared_sample()
+OUTPUT P^.Tag, " ", P^.Value, " ", P^.Count
+P^.Count <- (C_INT)9
+OUTPUT shared_count()
diff --git a/tests/iii/extern-struct-rejected/case.json b/tests/iii/extern-struct-rejected/case.json
new file mode 100644
index 0000000..6a4483f
--- /dev/null
+++ b/tests/iii/extern-struct-rejected/case.json
@@ -0,0 +1,12 @@
+{
+  "errors": [
+    {
+      "reason": "EXTERN\\ parameter\\ 1\\ of\\ puts\\ uses\\ record\\ Person,\\ which\\ is\\ not\\ a\\ C\\ struct:\\ field\\ Name\\ of\\ Person\\ has\\ type\\ STRING",
+      "line": 12
+    },
+    {
+      "reason": "EXTERN\\ parameter\\ 1\\ of\\ abs\\ cannot\\ be\\ record\\ Point\\ by\\ value;\\ use\\ a\\ pointer\\ type\\ to\\ it",
+      "line": 13
+    }
+  ]
+}
diff --git a/tests/iii/extern-struct-rejected/notes.md b/tests/iii/extern-struct-rejected/notes.md
new file mode 100644
index 0000000..f33ef66
--- /dev/null
+++ b/tests/iii/extern-struct-rejected/notes.md
@@ -0,0 +1,5 @@
+# extern-struct-rejected
+
+Compiler extension: an EXTERN signature accepts a record only as a C struct (every field a C type, a C struct or a pointer type to one) and, for now, only through a pointer type. Person has a STRING field, so a pointer to it is rejected and the field is named. Point is a C struct, but passing it by value is not supported yet.
+
+Require exit 1 and each cause on its EXTERN line.
diff --git a/tests/iii/extern-struct-rejected/program.cps b/tests/iii/extern-struct-rejected/program.cps
new file mode 100644
index 0000000..e7f38d1
--- /dev/null
+++ b/tests/iii/extern-struct-rejected/program.cps
@@ -0,0 +1,14 @@
+// Records cross the EXTERN boundary only as C structs through a pointer type.
+INCLUDE_OBJ "__libc"
+TYPE Person
+    DECLARE Name : STRING
+    DECLARE Age : C_INT
+ENDTYPE
+TYPE PPerson = ^Person
+TYPE Point
+    DECLARE X : C_INT
+    DECLARE Y : C_INT
+ENDTYPE
+EXTERN "C" EXTERN_PROCEDURE puts(PPerson)
+EXTERN "C" EXTERN_FUNCTION abs(Point) RETURNS C_INT
+OUTPUT 1