Disable clippy for submissions with dependencies (#72)

snippets/with_dependency/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "with_dependency"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+itertools = "*"

snippets/with_dependency/expected_analysis.json

@@ -0,0 +1,3 @@
+{
+  "comments": []
+}

snippets/with_dependency/src/lib.rs

@@ -0,0 +1,3 @@
+pub fn decrement(x: i32) -> i32 {
+    --x
+}

src/lib.rs

@@ -4,11 +4,23 @@ use anyhow::{Context, Result};
 use serde::Serialize;
 
 pub fn analyze_exercise(solution_dir: &Path) -> Result<AnalysisOutput> {
+    let manifest_path = solution_dir.join("Cargo.toml");
+    if std::fs::read_to_string(&manifest_path)
+        .context("failed to read Cargo.toml")?
+        .contains("[dependencies]")
+    {
+        // Do not run clippy on exercises that make use of dependencies.
+        // The analyzer currently has no support for dependencies like the
+        // test runner.
+        return Ok(AnalysisOutput { comments: vec![] });
+    }
+
     let clippy_output = Command::new("cargo")
         .arg("clippy")
+        .arg("--offline")
         .arg("--quiet") // suppress compilation progress output
         .arg("--manifest-path")
-        .arg(solution_dir.join("Cargo.toml").display().to_string())
+        .arg(manifest_path.display().to_string())
         .output()
         .context("failed to run clippy")?
         .stderr;