Add ensure option to cargo install

src/bin/cargo/commands/install.rs

@@ -24,6 +24,13 @@ pub fn cli() -> App {
         ))
         .arg_jobs()
         .arg(opt("force", "Force overwriting existing crates or binaries").short("f"))
+        .arg(
+            opt(
+                "ensure",
+                "Simply leaves it as-is when  you already have a suitable version",
+            )
+            .short("e"),
+        )
         .arg_features()
         .arg(opt("debug", "Build in debug mode instead of release mode"))
         .arg_targets_bins_examples(
@@ -128,6 +135,7 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
             version,
             &compile_opts,
             args.is_present("force"),
+            args.is_present("ensure"),
         )?;
     }
     Ok(())

src/cargo/ops/cargo_install.rs

@@ -42,6 +42,7 @@ pub fn install(
     vers: Option<&str>,
     opts: &ops::CompileOptions<'_>,
     force: bool,
+    ensure: bool,
 ) -> CargoResult<()> {
     let root = resolve_root(root, opts.config)?;
     let map = SourceConfigMap::new(opts.config)?;
@@ -56,6 +57,7 @@ pub fn install(
             vers,
             opts,
             force,
+            ensure,
             true,
         )?;
         (true, false)
@@ -75,6 +77,7 @@ pub fn install(
                 vers,
                 opts,
                 force,
+                ensure,
                 first,
             ) {
                 Ok(()) => succeeded.push(krate),
@@ -137,6 +140,7 @@ fn install_one(
     vers: Option<&str>,
     opts: &ops::CompileOptions<'_>,
     force: bool,
+    ensure: bool,
     is_first_install: bool,
 ) -> CargoResult<()> {
     let config = opts.config;
@@ -248,7 +252,7 @@ fn install_one(
         let metadata = metadata(config, root)?;
         let list = read_crate_list(&metadata)?;
         let dst = metadata.parent().join("bin");
-        check_overwrites(&dst, pkg, &opts.filter, &list, force)?;
+        check_overwrites(&dst, pkg, &opts.filter, &list, force, ensure)?;
     }
 
     let exec: Arc<dyn Executor> = Arc::new(DefaultExecutor);
@@ -287,7 +291,7 @@ fn install_one(
     let metadata = metadata(config, root)?;
     let mut list = read_crate_list(&metadata)?;
     let dst = metadata.parent().join("bin");
-    let duplicates = check_overwrites(&dst, pkg, &opts.filter, &list, force)?;
+    let duplicates = check_overwrites(&dst, pkg, &opts.filter, &list, force, ensure)?;
 
     fs::create_dir_all(&dst)?;
 
@@ -411,6 +415,7 @@ fn check_overwrites(
     filter: &ops::CompileFilter,
     prev: &CrateListingV1,
     force: bool,
+    ensure: bool,
 ) -> CargoResult<BTreeMap<String, Option<PackageId>>> {
     // If explicit --bin or --example flags were passed then those'll
     // get checked during cargo_compile, we only care about the "build
@@ -433,6 +438,12 @@ fn check_overwrites(
         }
     }
     msg.push_str("Add --force to overwrite");
+
+    if ensure {
+        eprintln!("{}", msg);
+        std::process::exit(0)
+    };
+
     Err(failure::format_err!("{}", msg))
 }
 

tests/testsuite/install.rs

@@ -504,6 +504,27 @@ foo v0.2.0 ([..]):
         .run();
 }
 
+#[test]
+fn install_ensure() {
+    let p = project()
+        .file("src/bin/foo-bin1.rs", "fn main() {}")
+        .file("src/bin/foo-bin2.rs", "fn main() {}")
+        .build();
+
+    cargo_process("install --ensure --path").arg(p.root()).run();
+    cargo_process("install --ensure --path")
+        .arg(p.root())
+        .with_stderr(
+            "\
+[INSTALLING] foo v0.0.1 [..]
+binary `foo-bin1[..]` already exists in destination as part of `foo v0.0.1 ([..])`
+binary `foo-bin2[..]` already exists in destination as part of `foo v0.0.1 ([..])`
+Add --force to overwrite
+",
+        )
+        .run();
+}
+
 #[test]
 fn install_force_partial_overlap() {
     let p = project()