Auto merge of #12766 - shnaramn:WarnAboutNameCase, r=epage

Warn about crate name's format when creating new crate

### What does this PR try to resolve?
Warns about a crate's name during creation (`crate new ...`) if it doesn't follow the preferred snake_case format.

Fixes #2708

The warning message uses the language mentioned in [RFC 430](https://github.com/rust-lang/rfcs/blob/master/text/0430-finalizing-naming-conventions.md#general-naming-conventions).

### How should we test and review this PR?
Verified existing tests succeeded with updates.  Added new tests to verify fix.

### Additional information
The link to [API naming guidelines](https://rust-lang.github.io/api-guidelines/naming.html) was not used since it still stays `unclear` for naming convention for crates.

Author: bors

src/cargo/ops/cargo_new.rs

@@ -258,6 +258,12 @@ fn check_name(
             name
         ))?;
     }
+    let name_in_lowercase = name.to_lowercase();
+    if name != name_in_lowercase {
+        shell.warn(format!(
+            "the name `{name}` is not snake_case or kebab-case which is recommended for package names, consider `{name_in_lowercase}`"
+        ))?;
+    }
 
     Ok(())
 }

tests/testsuite/new.rs

@@ -451,6 +451,7 @@ fn non_ascii_name() {
             "\
 [WARNING] the name `Привет` contains non-ASCII characters
 Non-ASCII crate names are not supported by Rust.
+[WARNING] the name `Привет` is not snake_case or kebab-case which is recommended for package names, consider `привет`
 [CREATED] binary (application) `Привет` package
 ",
         )
@@ -501,6 +502,29 @@ or change the name in Cargo.toml with:
         .run();
 }
 
+#[cargo_test]
+fn non_snake_case_name() {
+    cargo_process("new UPPERcase_name")
+        .with_stderr(
+            "\
+[WARNING] the name `UPPERcase_name` is not snake_case or kebab-case which is recommended for package names, consider `uppercase_name`
+[CREATED] binary (application) `UPPERcase_name` package
+",
+        )
+        .run();
+}
+
+#[cargo_test]
+fn kebab_case_name_is_accepted() {
+    cargo_process("new kebab-case-is-valid")
+        .with_stderr(
+            "\
+[CREATED] binary (application) `kebab-case-is-valid` package
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn git_default_branch() {
     // Check for init.defaultBranch support.