Better suggestion for redundant mode in build and install commands

src/bin/cargo/commands/build.rs

@@ -30,6 +30,7 @@ pub fn cli() -> Command {
         )
         .arg_features()
         .arg_release("Build artifacts in release mode, with optimizations")
+        .arg_redundant_default_mode("debug", "build", "release")
         .arg_profile("Build artifacts with the specified profile")
         .arg_parallel()
         .arg_target_triple("Build for the target triple")

src/bin/cargo/commands/install.rs

@@ -83,6 +83,7 @@ pub fn cli() -> Command {
             "debug",
             "Build in debug mode (with the 'dev' profile) instead of release mode",
         ))
+        .arg_redundant_default_mode("release", "install", "debug")
         .arg_profile("Install artifacts with the specified profile")
         .arg_target_triple("Build for the target triple")
         .arg_target_dir()

src/cargo/util/command_prelude.rs

@@ -112,6 +112,17 @@ pub trait CommandExt: Sized {
         self._arg(flag("keep-going", "").value_parser(value_parser).hide(true))
     }
 
+    fn arg_redundant_default_mode(
+        self,
+        default_mode: &'static str,
+        command: &'static str,
+        supported_mode: &'static str,
+    ) -> Self {
+        let msg = format!("`--{default_mode}` is the default for `cargo {command}`; instead `--{supported_mode}` is supported");
+        let value_parser = UnknownArgumentValueParser::suggest(msg);
+        self._arg(flag(default_mode, "").value_parser(value_parser).hide(true))
+    }
+
     fn arg_targets_all(
         self,
         lib: &'static str,
@@ -486,7 +497,7 @@ Run `{cmd}` to see possible targets."
             (Some(name @ ("dev" | "test" | "bench" | "check")), ProfileChecking::LegacyRustc)
             // `cargo fix` and `cargo check` has legacy handling of this profile name
             | (Some(name @ "test"), ProfileChecking::LegacyTestOnly) => {
-                if self.flag("release") {
+                if self.maybe_flag("release") {
                     config.shell().warn(
                         "the `--release` flag should not be specified with the `--profile` flag\n\
                          The `--release` flag will be ignored.\n\
@@ -510,7 +521,11 @@ Run `{cmd}` to see possible targets."
             )
         };
 
-        let name = match (self.flag("release"), self.flag("debug"), specified_profile) {
+        let name = match (
+            self.maybe_flag("release"),
+            self.maybe_flag("debug"),
+            specified_profile,
+        ) {
             (false, false, None) => default,
             (true, _, None | Some("release")) => "release",
             (true, _, Some(name)) => return Err(conflict("release", "release", name)),

tests/testsuite/build.rs

@@ -135,6 +135,29 @@ fn incremental_config() {
         .run();
 }
 
+#[cargo_test]
+fn cargo_compile_with_redundant_default_mode() {
+    let p = project()
+        .file("Cargo.toml", &basic_bin_manifest("foo"))
+        .file("src/foo.rs", &main_file(r#""i am foo""#, &[]))
+        .build();
+
+    p.cargo("build --debug")
+        .with_stderr(
+            "\
+error: unexpected argument '--debug' found
+
+  tip: `--debug` is the default for `cargo build`; instead `--release` is supported
+
+Usage: cargo[EXE] build [OPTIONS]
+
+For more information, try '--help'.
+",
+        )
+        .with_status(1)
+        .run();
+}
+
 #[cargo_test]
 fn cargo_compile_with_workspace_excluded() {
     let p = project().file("src/main.rs", "fn main() {}").build();

tests/testsuite/install.rs

@@ -2443,3 +2443,23 @@ fn ambiguous_registry_vs_local_package() {
         .run();
     assert_has_installed_exe(cargo_home(), "foo");
 }
+
+#[cargo_test]
+fn install_with_redundant_default_mode() {
+    pkg("foo", "0.0.1");
+
+    cargo_process("install foo --release")
+        .with_stderr(
+            "\
+error: unexpected argument '--release' found
+
+  tip: `--release` is the default for `cargo install`; instead `--debug` is supported
+
+Usage: cargo[EXE] install [OPTIONS] [crate]...
+
+For more information, try '--help'.
+",
+        )
+        .with_status(1)
+        .run();
+}