feat: Don't check antivirus when few binaries are affected

This is very much a heuristic to avoid outputting the note to users
where it might not be relevant.

Author: madsmtm

src/cargo/ops/cargo_compile/mod.rs

@@ -43,7 +43,7 @@ use crate::core::compiler::UserIntent;
 use crate::core::compiler::unit_dependencies::build_unit_dependencies;
 use crate::core::compiler::unit_graph::{self, UnitDep, UnitGraph};
 use crate::core::compiler::{BuildConfig, BuildContext, BuildRunner, Compilation};
-use crate::core::compiler::{CompileKind, CompileTarget, RustcTargetData, Unit};
+use crate::core::compiler::{CompileKind, CompileMode, CompileTarget, RustcTargetData, Unit};
 use crate::core::compiler::{CrateType, TargetInfo, apply_env_config, standard_lib};
 use crate::core::compiler::{DefaultExecutor, Executor, UnitInterner};
 use crate::core::profiles::Profiles;
@@ -561,15 +561,34 @@ where `<compatible-ver>` is the latest version supporting rustc {rustc_version}"
     }
 
     if build_config.detect_antivirus {
-        // TODO(madsmtm): Maybe only do this when we have above a certain
-        // number of build scripts or test binaries to run?
+        // Count the number of test binaries and build scripts we'll need to
+        // run. This doesn't take into account the binary that will be run
+        // if `cargo run` was specified, and doesn't handle pre-2024 `rustdoc`
+        // tests, but that's fine, this is only a heuristic.
+        let num_binaries = unit_graph
+            .keys()
+            .filter(|unit| {
+                matches!(
+                    unit.mode,
+                    CompileMode::Test | CompileMode::Doctest | CompileMode::RunCustomBuild
+                )
+            })
+            .count();
+
+        tracing::debug!("estimated {num_binaries} binaries that could be slowed down by antivirus");
 
         // TODO(madsmtm): Consider only warning once every X days.
 
-        // We don't want to do this check when installing, since there might
-        // be `cargo install` users who are not necessarily developers (and so
-        // the note will be irrelevant to them).
-        if build_config.intent != UserIntent::Install {
+        // Heuristic: Only do the check if we have to run more than a specific
+        // number of binaries. This makes it so that small beginner projects
+        // don't hit this.
+        //
+        // TODO(madsmtm): What should the threshold be?
+        //
+        // We also don't want to do this check when installing, since there
+        // might be `cargo install` users who are not necessarily developers
+        // (and so the note will be irrelevant to them).
+        if 10 < num_binaries && build_config.intent != UserIntent::Install {
             if let Err(err) = detect_antivirus::detect_and_report(gctx) {
                 // Errors in this detection are not fatal.
                 tracing::error!("failed detecting whether binaries may be slow to run: {err}");