Rust: switch to .rust-project.json from Cargo.toml for running tests

rust/ql/test/.gitignore

@@ -1,4 +1,5 @@
 Cargo.toml
 Cargo.lock
+.rust-project.json
 lib.rs
 target/

rust/tools/qltest.sh

@@ -5,8 +5,21 @@ mkdir -p "$CODEQL_EXTRACTOR_RUST_TRAP_DIR"
 export RUST_BACKTRACE=full
 
 QLTEST_LOG="$CODEQL_EXTRACTOR_RUST_LOG_DIR"/qltest.log
-
 EXTRACTOR="$CODEQL_EXTRACTOR_RUST_ROOT/tools/$CODEQL_PLATFORM/extractor"
+sysroot="$(rustc --print sysroot)"
+sysroot_src="$sysroot/lib/rustlib/src/rust/library"
+if [ ! -d "$sysroot_src" ]; then
+  echo "rustlib source must be available" >&2
+  if [[ "$CODEQL_THREADS" != 1 ]]; then
+    echo "refusing to run rustup in parallel mode, please run" >&2
+    echo "  rustup component add rust-src" >&2
+    echo "and try again" >&2
+    exit 1
+  fi
+  echo "running rustup to fetch it" >&2
+  rustup component add rust-src
+fi
+
 echo > lib.rs
 for src in *.rs; do
   if [[ "$src" == "lib.rs" ]]; then
@@ -17,7 +30,9 @@ for src in *.rs; do
     echo "mod ${src%.rs};" >> lib.rs
   fi
 done
-cat > Cargo.toml << EOF
+if [[ "$CODEQL_EXTRACTOR_RUST_TEST_GENERATE_CARGO" = true ]]; then
+  rm -f .rust-project.json
+  cat > Cargo.toml << EOF
 [workspace]
 [package]
 name = "test"
@@ -26,14 +41,40 @@ edition="2021"
 [lib]
 path="lib.rs"
 EOF
-if [[ -f "main.rs" ]]; then
-cat >> Cargo.toml << EOF
+  if [[ -f "main.rs" ]]; then
+    cat >> Cargo.toml << EOF
 [[bin]]
 name = "main"
 path = "main.rs"
 EOF
+  fi
+else
+  rm -f Cargo.{toml,lock}
+  cat > .rust-project.json << EOF
+{
+  "sysroot": "$sysroot",
+  "sysroot_src": "$sysroot_src",
+  "crates": [
+    {
+      "root_module": "lib.rs",
+      "edition": "2021",
+      "deps": []
+    }
+EOF
+  if [[ -f "main.rs" ]]; then
+    cat >> .rust-project.json << EOF
+    ,
+    {
+      "root_module": "main.rs",
+      "edition": "2021",
+      "deps": [{"crate": 0, "name": "lib"}]
+    }
+EOF
+  fi
+  echo -e "  ]\n}" >> .rust-project.json
 fi
-"$EXTRACTOR" *.rs >> "$QLTEST_LOG"
+
+"$EXTRACTOR" *.rs &>> "$QLTEST_LOG"
 if [[ "$?" != 0 ]]; then
   cat "$QLTEST_LOG" # Show compiler errors on extraction failure
   exit 1