coverage: Run-make regression test for #[derive(arbitrary::Arbitrary)]

Author: Zalathar

src/tools/run-make-support/src/external_deps/llvm.rs

@@ -17,6 +17,13 @@ pub fn llvm_profdata() -> LlvmProfdata {
     LlvmProfdata::new()
 }
 
+/// Constructs a new `llvm-cov` invocation.
+/// This assumes that `llvm-cov` is available at `$LLVM_BIN_DIR/llvm-cov`.
+#[track_caller]
+pub fn llvm_cov() -> LlvmCov {
+    LlvmCov::new()
+}
+
 /// Construct a new `llvm-filecheck` invocation. This assumes that `llvm-filecheck` is available
 /// at `$LLVM_FILECHECK`.
 #[track_caller]
@@ -86,6 +93,13 @@ pub struct LlvmProfdata {
     cmd: Command,
 }
 
+/// An `llvm-cov` invocation builder.
+#[derive(Debug)]
+#[must_use]
+pub struct LlvmCov {
+    cmd: Command,
+}
+
 /// A `llvm-filecheck` invocation builder.
 #[derive(Debug)]
 #[must_use]
@@ -151,6 +165,7 @@ pub struct LlvmObjcopy {
 
 crate::macros::impl_common_helpers!(LlvmReadobj);
 crate::macros::impl_common_helpers!(LlvmProfdata);
+crate::macros::impl_common_helpers!(LlvmCov);
 crate::macros::impl_common_helpers!(LlvmFilecheck);
 crate::macros::impl_common_helpers!(LlvmObjdump);
 crate::macros::impl_common_helpers!(LlvmAr);
@@ -259,6 +274,17 @@ impl LlvmProfdata {
     }
 }
 
+impl LlvmCov {
+    /// Constructs a new `llvm-cov` invocation.
+    /// This assumes that `llvm-cov` is available at `$LLVM_BIN_DIR/llvm-cov`.
+    #[track_caller]
+    pub fn new() -> Self {
+        let llvm_cov = llvm_bin_dir().join("llvm-cov");
+        let cmd = Command::new(llvm_cov);
+        Self { cmd }
+    }
+}
+
 impl LlvmFilecheck {
     /// Construct a new `llvm-filecheck` invocation. This assumes that `llvm-filecheck` is available
     /// at `$LLVM_FILECHECK`.

tests/run-make/coverage-arbitrary/Cargo.lock

@@ -0,0 +1,65 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "arbitrary"
+version = "1.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dde20b3d026af13f561bdd0f15edf01fc734f0dafcedbaf42bba506a9517f223"
+dependencies = [
+ "derive_arbitrary",
+]
+
+[[package]]
+name = "coverage-arbitrary"
+version = "0.0.0"
+dependencies = [
+ "arbitrary",
+]
+
+[[package]]
+name = "derive_arbitrary"
+version = "1.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "30542c1ad912e0e3d22a1935c290e12e8a29d704a420177a31faad4a601a0800"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.95"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "02b3e5e68a3a1a02aad3ec490a98007cbc13c37cbe84a3cd7b8e406d76e7f778"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.40"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1885c039570dc00dcb4ff087a89e185fd56bae234ddc7f056a945bf36467248d"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.104"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "17b6f705963418cdb9927482fa304bc562ece2fdd4f616084c50b7023b435a40"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a5f39404a5da50712a4c1eecf25e90dd62b613502b7e925fd4e4d19b5c96512"

tests/run-make/coverage-arbitrary/Cargo.toml

@@ -0,0 +1,9 @@
+[workspace]
+resolver = "2"
+
+[package]
+name = "coverage-arbitrary-crate"
+edition = "2024"
+
+[dependencies]
+arbitrary = { version = "1.4.1", features = ["derive"] }

tests/run-make/coverage-arbitrary/rmake.rs

@@ -0,0 +1,35 @@
+//! Regression test for edge-case bugs in coverage instrumentation that have
+//! historically been triggered by derived `arbitrary::Arbitrary` impls.
+//!
+//! See <https://github.com/rust-lang/rust/issues/141577#issuecomment-3120667286>
+//! for an example of one such bug.
+
+use run_make_support::{cargo, is_windows, llvm};
+
+fn main() {
+    let profraw_path = "default.profraw";
+    let profdata_path = "default.profdata";
+
+    // Build and run the crate with coverage instrumentation,
+    // producing a `.profraw` file.
+    let run_out = cargo()
+        .args(&["run", "--manifest-path=Cargo.toml", "--release"])
+        .env("RUSTFLAGS", "-Cinstrument-coverage")
+        .env("LLVM_PROFILE_FILE", profraw_path)
+        .run();
+
+    // The program prints its own executable path (i.e. args[0]) to stdout.
+    let exe_path = run_out.stdout_utf8().lines().next().unwrap().to_owned();
+
+    // Convert `.profraw` output to `.profdata`, as needed by `llvm-cov`.
+    llvm::llvm_profdata()
+        .args(&["merge", "--sparse", "--output", profdata_path, profraw_path])
+        .run();
+
+    // The contents of the coverage report are not very important;
+    // what matters is that `llvm-cov` should not encounter an error
+    // (e.g. "malformed instrumentation profile data: function name is empty").
+    llvm::llvm_cov()
+        .args(&["show", "-format=text", "-instr-profile", profdata_path, "-object", &exe_path])
+        .run();
+}

tests/run-make/coverage-arbitrary/src/main.rs

@@ -0,0 +1,30 @@
+use core::hint::black_box;
+use std::env::args;
+
+use arbitrary::{Arbitrary, Unstructured};
+
+#[derive(Debug, Arbitrary)]
+struct MyStruct {
+    _x: u32,
+}
+
+#[derive(Debug, Arbitrary)]
+enum MyEnum {
+    One,
+    Two,
+    Three,
+}
+
+fn main() {
+    // Print the executable path to stdout, so that the rmake script has easy
+    // access to it. This is easier than trying to interrogate cargo.
+    println!("{}", args().nth(0).unwrap());
+
+    dbg!(MyStruct::size_hint(0));
+    dbg!(MyEnum::size_hint(0));
+
+    let mut data = Unstructured::new(black_box(&[0; 1024]));
+
+    dbg!(MyStruct::arbitrary(&mut data));
+    dbg!(MyEnum::arbitrary(&mut data));
+}