install: Added error message for when v is prefixed with version

Author: Pyr0de

src/bin/cargo/commands/install.rs

@@ -286,6 +286,12 @@ fn parse_semver_flag(v: &str) -> CargoResult<VersionReq> {
         .next()
         .ok_or_else(|| format_err!("no version provided for the `--version` flag"))?;
 
+    if let Some(stripped) = v.strip_prefix("v") {
+        bail!(
+            "the version provided, `{v}` is not a valid SemVer requirement\n\n\
+            help: try changing the version to `{stripped}`",
+        )
+    }
     let is_req = "<>=^~".contains(first) || v.contains('*');
     if is_req {
         match v.parse::<VersionReq>() {

tests/testsuite/install.rs

@@ -2906,7 +2906,9 @@ fn prefixed_v_in_version() {
     cargo_process("install [email protected]")
         .with_status(1)
         .with_stderr_data(str![[r#"
-[ERROR] invalid value '[email protected]' for '[CRATE[@<VER>]]...': unexpected character 'v' while parsing major version number
+[ERROR] invalid value '[email protected]' for '[CRATE[@<VER>]]...': the version provided, `v0.0.1` is not a valid SemVer requirement
+
+[HELP] try changing the version to `0.0.1`
 
 For more information, try '--help'.