Auto merge of #11835 - domsleee:git-install-bin-flag-hint, r=weihanglo

`cargo install --git` multiple packages with binaries found hint

### What does this PR try to resolve?
The issues discussed in: #4830

namely this one:
> 4. a multiple packages with binaries found error should give users a hint about how to specify a single crate

I think improving the error message to provide a suggestion is a simple change that would help a lot of people when this happens, sorry if I'm out of line for just opening a PR here :)

### Before
cargo 1.68.0 (115f345 2023-02-26)
![image](https://user-images.githubusercontent.com/14891742/224546157-d9b48bfd-f896-4fd1-9f0a-e04a3ad60ae2.png)

### After
![image](https://user-images.githubusercontent.com/14891742/224546182-d4b451ae-1b28-41b6-9d74-db860532512b.png)

### Additional information

I added in a related test documenting existing behaviours
* multiple_examples_error: "multiple packages with examples found" (i.e. not "binaries")

I added these tests which aren't necessarily related to this PR, but could be considered if the behaviour were to change
* `multiple_binaries_deep_select_uses_package_name`: it uses the name, not the path. Is this a problem for crates with the same name?
* `multiple_binaries_in_selected_package_installs_all`: so `--bins` is implied when a package is specified?
* `multiple_binaries_in_selected_package_with_bin_option_installs_only_one`: demonstrates a use case where `--bin` and `[crate]` are both used

Author: bors

src/cargo/ops/common_for_install_and_uninstall.rs

@@ -616,9 +616,10 @@ where
         let examples = candidates
             .iter()
             .filter(|cand| cand.targets().iter().filter(|t| t.is_example()).count() > 0);
-        let pkg = match one(binaries, |v| multi_err("binaries", v))? {
+        let git_url = source.source_id().url().to_string();
+        let pkg = match one(binaries, |v| multi_err("binaries", &git_url, v))? {
             Some(p) => p,
-            None => match one(examples, |v| multi_err("examples", v))? {
+            None => match one(examples, |v| multi_err("examples", &git_url, v))? {
                 Some(p) => p,
                 None => bail!(
                     "no packages found with binaries or \
@@ -629,17 +630,20 @@ where
         Ok(pkg.clone())
     };
 
-    fn multi_err(kind: &str, mut pkgs: Vec<&Package>) -> String {
+    fn multi_err(kind: &str, git_url: &str, mut pkgs: Vec<&Package>) -> String {
         pkgs.sort_unstable_by_key(|a| a.name());
+        let first_pkg = pkgs[0];
         format!(
             "multiple packages with {} found: {}. When installing a git repository, \
-            cargo will always search the entire repo for any Cargo.toml. \
-            Please specify which to install.",
+            cargo will always search the entire repo for any Cargo.toml.\n\
+            Please specify a package, e.g. `cargo install --git {} {}`.",
             kind,
             pkgs.iter()
                 .map(|p| p.name().as_str())
                 .collect::<Vec<_>>()
-                .join(", ")
+                .join(", "),
+            git_url,
+            first_pkg.name()
         )
     }
 }

tests/testsuite/install.rs

@@ -560,28 +560,109 @@ Available binaries:
 }
 
 #[cargo_test]
-fn multiple_crates_error() {
+fn multiple_packages_containing_binaries() {
     let p = git::repo(&paths::root().join("foo"))
         .file("Cargo.toml", &basic_manifest("foo", "0.1.0"))
         .file("src/main.rs", "fn main() {}")
         .file("a/Cargo.toml", &basic_manifest("bar", "0.1.0"))
         .file("a/src/main.rs", "fn main() {}")
         .build();
 
+    let git_url = p.url().to_string();
     cargo_process("install --git")
         .arg(p.url().to_string())
         .with_status(101)
-        .with_stderr(
+        .with_stderr(format!(
             "\
 [UPDATING] git repository [..]
 [ERROR] multiple packages with binaries found: bar, foo. \
-When installing a git repository, cargo will always search the entire repo for any Cargo.toml. \
-Please specify which to install.
-",
-        )
+When installing a git repository, cargo will always search the entire repo for any Cargo.toml.
+Please specify a package, e.g. `cargo install --git {git_url} bar`.
+"
+        ))
+        .run();
+}
+
+#[cargo_test]
+fn multiple_packages_matching_example() {
+    let p = git::repo(&paths::root().join("foo"))
+        .file("Cargo.toml", &basic_manifest("foo", "0.1.0"))
+        .file("src/lib.rs", "")
+        .file("examples/ex1.rs", "fn main() {}")
+        .file("bar/Cargo.toml", &basic_manifest("bar", "0.1.0"))
+        .file("bar/src/lib.rs", "")
+        .file("bar/examples/ex1.rs", "fn main() {}")
+        .build();
+
+    let git_url = p.url().to_string();
+    cargo_process("install --example ex1 --git")
+        .arg(p.url().to_string())
+        .with_status(101)
+        .with_stderr(format!(
+            "\
+[UPDATING] git repository [..]
+[ERROR] multiple packages with examples found: bar, foo. \
+When installing a git repository, cargo will always search the entire repo for any Cargo.toml.
+Please specify a package, e.g. `cargo install --git {git_url} bar`."
+        ))
         .run();
 }
 
+#[cargo_test]
+fn multiple_binaries_deep_select_uses_package_name() {
+    let p = git::repo(&paths::root().join("foo"))
+        .file("Cargo.toml", &basic_manifest("foo", "0.1.0"))
+        .file("src/main.rs", "fn main() {}")
+        .file("bar/baz/Cargo.toml", &basic_manifest("baz", "0.1.0"))
+        .file("bar/baz/src/main.rs", "fn main() {}")
+        .build();
+
+    cargo_process("install --git")
+        .arg(p.url().to_string())
+        .arg("baz")
+        .run();
+}
+
+#[cargo_test]
+fn multiple_binaries_in_selected_package_installs_all() {
+    let p = git::repo(&paths::root().join("foo"))
+        .file("Cargo.toml", &basic_manifest("foo", "0.1.0"))
+        .file("src/lib.rs", "")
+        .file("bar/Cargo.toml", &basic_manifest("bar", "0.1.0"))
+        .file("bar/src/bin/bin1.rs", "fn main() {}")
+        .file("bar/src/bin/bin2.rs", "fn main() {}")
+        .build();
+
+    cargo_process("install --git")
+        .arg(p.url().to_string())
+        .arg("bar")
+        .run();
+
+    let cargo_home = cargo_home();
+    assert_has_installed_exe(&cargo_home, "bin1");
+    assert_has_installed_exe(&cargo_home, "bin2");
+}
+
+#[cargo_test]
+fn multiple_binaries_in_selected_package_with_bin_option_installs_only_one() {
+    let p = git::repo(&paths::root().join("foo"))
+        .file("Cargo.toml", &basic_manifest("foo", "0.1.0"))
+        .file("src/lib.rs", "")
+        .file("bar/Cargo.toml", &basic_manifest("bar", "0.1.0"))
+        .file("bar/src/bin/bin1.rs", "fn main() {}")
+        .file("bar/src/bin/bin2.rs", "fn main() {}")
+        .build();
+
+    cargo_process("install --bin bin1 --git")
+        .arg(p.url().to_string())
+        .arg("bar")
+        .run();
+
+    let cargo_home = cargo_home();
+    assert_has_installed_exe(&cargo_home, "bin1");
+    assert_has_not_installed_exe(&cargo_home, "bin2");
+}
+
 #[cargo_test]
 fn multiple_crates_select() {
     let p = git::repo(&paths::root().join("foo"))