Fix warning, make them errors in CI (#693)

.github/workflows/tests.yml

@@ -6,6 +6,7 @@ env:
   CARGO_TERM_COLOR: always
   CLICOLOR_FORCE: 1
   RUSTDOCFLAGS: "-Dwarnings"
+  RUSTFLAGS: "-D warnings"
 
 jobs:
   test-latest:

cargo-insta/tests/functional/inline.rs

@@ -24,6 +24,7 @@ serde = { version = "1.0", features = ["derive"] }
             r#"
 use serde::Serialize;
 
+#[allow(dead_code)]
 #[derive(Serialize)]
 struct User {
     id: u64,
@@ -56,7 +57,7 @@ fn test_json_snapshot() {
     assert_snapshot!(test_project.diff("src/lib.rs"), @r##"
     --- Original: src/lib.rs
     +++ Updated: src/lib.rs
-    @@ -15,5 +15,10 @@
+    @@ -16,5 +16,10 @@
          };
          insta::assert_json_snapshot!(&user, {
              ".id" => "[user_id]",
@@ -93,6 +94,7 @@ serde = { version = "1.0", features = ["derive"] }
             r#"
 use serde::Serialize;
 
+#[allow(dead_code)]
 #[derive(Serialize)]
 struct User {
     id: u64,
@@ -122,10 +124,10 @@ fn test_yaml_snapshot() {
 
     assert!(&output.status.success());
 
-    assert_snapshot!(test_project.diff("src/lib.rs"), @r###"
+    assert_snapshot!(test_project.diff("src/lib.rs"), @r##"
     --- Original: src/lib.rs
     +++ Updated: src/lib.rs
-    @@ -15,5 +15,8 @@
+    @@ -16,5 +16,8 @@
          };
          insta::assert_yaml_snapshot!(&user, {
              ".id" => "[user_id]",
@@ -135,7 +137,7 @@ fn test_yaml_snapshot() {
     +    email: [email protected]
     +    "#);
      }
-    "###);
+    "##);
 }
 
 #[test]

insta/src/env.rs

@@ -4,7 +4,7 @@ use std::path::{Path, PathBuf};
 use std::sync::{Arc, Mutex};
 use std::{env, fmt, fs};
 
-use crate::utils::{get_cargo, is_ci};
+use crate::utils::is_ci;
 use crate::{
     content::{yaml, Content},
     elog,
@@ -42,6 +42,7 @@ impl TestRunner {
     /// Fall back to `cargo test` if `cargo nextest` isn't installed and
     /// `test_runner_fallback` is true
     pub fn resolve_fallback(&self, test_runner_fallback: bool) -> &TestRunner {
+        use crate::utils::get_cargo;
         if self == &TestRunner::Nextest
             && test_runner_fallback
             && std::process::Command::new(get_cargo())

insta/src/utils.rs

@@ -108,6 +108,7 @@ pub fn format_rust_expression(value: &str) -> Cow<'_, str> {
     Cow::Borrowed(value)
 }
 
+#[cfg(feature = "_cargo_insta_internal")]
 pub fn get_cargo() -> std::ffi::OsString {
     let cargo = env::var_os("CARGO");
     let cargo = cargo