add test for memory usage in worse-case scenario

gix-config/tests/Cargo.toml

@@ -14,6 +14,10 @@ publish = false
 name = "config"
 path = "config.rs"
 
+[[test]]
+name = "mem"
+path = "mem.rs"
+
 [dev-dependencies]
 gix-config = { path = ".."}
 gix-testtools = { path = "../../tests/tools"}
@@ -23,3 +27,6 @@ gix-path = { path = "../../gix-path" }
 gix-sec = { path = "../../gix-sec" }
 serial_test = { version = "2.0.0", default-features = false }
 bstr = { version = "1.3.0", default-features = false, features = ["std"] }
+
+bytesize = "1.3.0"
+cap = { version = "0.1.2", features = ["stats"] }

gix-config/tests/config.rs

@@ -1,6 +1,7 @@
 pub use gix_testtools::Result;
 
 mod file;
+mod mem;
 mod parse;
 mod source;
 mod value;

gix-config/tests/fixtures/fuzzed/.gitattributes

@@ -0,0 +1 @@
+*.config -text -eof

gix-config/tests/mem.rs

@@ -0,0 +1,33 @@
+use bytesize::ByteSize;
+use cap::Cap;
+use std::alloc;
+use std::time::Instant;
+
+#[global_allocator]
+static ALLOCATOR: Cap<alloc::System> = Cap::new(alloc::System, usize::max_value());
+
+#[test]
+fn usage() {
+    let before = ALLOCATOR.allocated();
+    let start = Instant::now();
+    let config = gix_config::File::from_bytes_no_includes(
+        include_bytes!("fixtures/fuzzed/mem-amplification.config"),
+        gix_config::file::Metadata::from(gix_config::Source::User),
+        Default::default(),
+    )
+    .unwrap();
+    let after = ALLOCATOR.allocated();
+    let used = after - before;
+    let elapsed = start.elapsed().as_secs_f32();
+    eprintln!(
+        "used mem: {}B for {} sections, took {elapsed:.02}s [total-mem: {total}, peak-mem: {peak}]",
+        ByteSize(used as u64),
+        config.sections().count(),
+        total = ByteSize(ALLOCATOR.total_allocated() as u64),
+        peak = ByteSize(ALLOCATOR.max_allocated() as u64),
+    );
+    assert!(
+        used < 60 * 1024 * 1024,
+        "we should now start using more memory than anticipated, to keep mem-amplification low"
+    );
+}