cargo_embargo: detect and ignore harness-less tests

These currently cause cargo_embargo to fail. We should support them
eventually, but for now we'll ignore them to unblock crosvm merges.

Test: external/crosvm/android-merge-2-cargo-embargo.sh
Bug: 275386231
Change-Id: I3e156afa5672ddd6257c7caabd05346e060448fb

tools/cargo_embargo/src/cargo_out.rs

@@ -35,6 +35,8 @@ pub enum CrateType {
     ProcMacro,
     // --test
     Test,
+    // "--cfg test" without --test. (Assume it is a test with the harness disabled.
+    TestNoHarness,
 }
 
 /// Info extracted from `CargoOut` for a crate.
@@ -383,8 +385,13 @@ impl Crate {
         if out.main_src.as_os_str().is_empty() {
             bail!("missing main source file");
         }
+        // Must have at least one type.
         if out.types.is_empty() {
-            bail!("must specify one of --test or --crate-type");
+            if out.cfgs.contains(&"test".to_string()) {
+                out.types.push(CrateType::TestNoHarness);
+            } else {
+                bail!("failed to detect crate type. did not have --crate-type or --test or '--cfg test'");
+            }
         }
         if out.types.contains(&CrateType::Test) && out.types.len() != 1 {
             bail!("cannot specify both --test and --crate-type");

tools/cargo_embargo/src/main.rs

@@ -360,7 +360,14 @@ fn write_android_bp(
     };
 
     for c in crates {
-        modules.extend(crate_to_bp_modules(c, cfg, package_cfg, &extra_srcs)?);
+        modules.extend(crate_to_bp_modules(c, cfg, package_cfg, &extra_srcs).with_context(
+            || {
+                format!(
+                    "failed to generate bp module for crate \"{}\" with package name \"{}\"",
+                    c.name, c.package_name
+                )
+            },
+        )?);
     }
     if modules.is_empty() {
         return Ok(());
@@ -444,10 +451,17 @@ fn crate_to_bp_modules(
                 let stem = "lib".to_string() + &crate_.name;
                 ("rust_proc_macro".to_string(), stem.clone(), stem)
             }
-            CrateType::Test => {
+            CrateType::Test | CrateType::TestNoHarness => {
                 let suffix = crate_.main_src.to_string_lossy().into_owned();
                 let suffix = suffix.replace('/', "_").replace(".rs", "");
                 let stem = crate_.package_name.clone() + "_test_" + &suffix;
+                if crate_type == &CrateType::TestNoHarness {
+                    eprintln!(
+                        "WARNING: ignoring test \"{}\" with harness=false. not supported yet",
+                        stem
+                    );
+                    return Ok(Vec::new());
+                }
                 ("rust_test".to_string() + host, stem.clone(), stem)
             }
         };