rt: memreport marks a leaked value whose drop never ran with (drop); spec 4.11, readme, memdebug_report_drop.zc

4 files changed, 20 insertions, 3 deletions

diff --git a/README.md b/README.md
index 4ebbe0e..a90017d 100644
--- a/README.md
+++ b/README.md
@@ -272,7 +272,7 @@ zy: double free from line 12
 zy: bad heap pointer
 ```
 
-the line is the `new` that made the block. a double free prints and returns; it does not smash the block. `rt.memreport()` prints one line per recorded object that is still live, `leak: line 12 3 words`, and returns how many. the word count is the block's payload, which is a power-of-two chunk minus the 5 word header, not the size you asked for. the table holds 64 sites. freed blocks stay in it until the storage is reused, which is how a double free still knows the line. nothing here changes programs that never say `memdebug`.
+the line is the `new` that made the block. a double free prints and returns; it does not smash the block. `rt.memreport()` prints one line per recorded object that is still live, `leak: line 12 3 words` (with ` (drop)` after it when the object's drop never ran), and returns how many. the word count is the block's payload, which is a power-of-two chunk minus the 5 word header, not the size you asked for. the table holds 64 sites. freed blocks stay in it until the storage is reused, which is how a double free still knows the line. nothing here changes programs that never say `memdebug`.
 
 ### line tables and backtraces
 
diff --git a/docs/SPEC.md b/docs/SPEC.md
index 4406123..bb0f44f 100644
--- a/docs/SPEC.md
+++ b/docs/SPEC.md
@@ -629,7 +629,7 @@ o3 int sum(fixed int[?] a) { int s = 0; for (int i = 0; i < len(a); i++) s += a[
 
 ### 4.11 memdebug
 
-`memdebug on;` turns on heap header checks and allocation-site tracking from this point in the file (top level) or from this point in the function (statement); the runtime enables the checks before `main` for the top-level form. `memdebug scrub;` additionally fills freed payloads with 57005; `memdebug off;` stops. with checks on, a use after free prints `zy: use after free from line N`, a double free prints `zy: double free from line N` and returns, a stray address prints `zy: bad heap pointer`. `rt.memreport()` prints a line `leak: line N W words` per live recorded object (W is the n words new asked for, not the block's payload) and returns the count.
+`memdebug on;` turns on heap header checks and allocation-site tracking from this point in the file (top level) or from this point in the function (statement); the runtime enables the checks before `main` for the top-level form. `memdebug scrub;` additionally fills freed payloads with 57005; `memdebug off;` stops. with checks on, a use after free prints `zy: use after free from line N`, a double free prints `zy: double free from line N` and returns, a stray address prints `zy: bad heap pointer`. `rt.memreport()` prints a line `leak: line N W words` per live recorded object (W is the n words new asked for, not the block's payload), with ` (drop)` after it when the object has a drop that hasn't run (6.15: a leaked resource), and returns the count.
 
 ### 4.12 hints
 
diff --git a/src/runtime/rt.zc b/src/runtime/rt.zc
index 099ca2e..3d448b0 100644
--- a/src/runtime/rt.zc
+++ b/src/runtime/rt.zc
@@ -1627,7 +1627,9 @@ int memreport() {
 		if (site_p[i]) {
 			p = site_p[i] ^ MAGIC;
 			if (isobj(p)) {
-				put_s("leak: line "); put_n(site_line[i]); put_s(" "); put_n(paylen(p)); put_s(" words\n");	// n, the words new asked for
+				put_s("leak: line "); put_n(site_line[i]); put_s(" "); put_n(paylen(p)); put_s(" words");	// n, the words new asked for
+				if ((p[-4] & (F_HASDROP | F_DROPPED)) == F_HASDROP) put_s(" (drop)");	// a leaked resource: its drop never ran
+				put_c(10);
 				n++;
 			}
 		}
diff --git a/tests/conformance/4-statements/memdebug_report_drop.zc b/tests/conformance/4-statements/memdebug_report_drop.zc
new file mode 100644
index 0000000..cf33b69
--- /dev/null
+++ b/tests/conformance/4-statements/memdebug_report_drop.zc
@@ -0,0 +1,15 @@
+// expect: leak: line 9 1 words (drop)/leak: line 10 2 words/207/
+// spec 4.11, 6.15: rt.memreport() marks a leaked value whose drop never ran with (drop): a leaked resource, not just words
+include rt;
+void pn(int x) { rt.put_n(x); rt.put_c(10); }
+struct res { int fd; void drop() { rt.put_s("closed "); } }
+memdebug on;
+fn main() {
+	unchecked {
+		res* f = rt.new(res);
+		int* q = rt.new(2);
+		pn(rt.memreport() * 100 + 7);
+	}
+	return 0;
+}
+// zc0: skip