Normalize --path to install bin outside current workspace

For `Workspace::find_root`, `cargo_util::path::PathAncestors` won't do
path normalization while walking back the ancestors. The responsibility
lies in the caller. Thus, `cargo install` should normalize its `--path`
argument before passing in `SourceId::for_path` and `Workspace::new`.

`Config::reload_rooted_at` is not affected because cargo always starts
searching and merging configs from where it is invoked.

src/bin/cargo/commands/install.rs

@@ -1,9 +1,11 @@
 use crate::command_prelude::*;
 
-use cargo::core::{GitReference, SourceId};
+use cargo::core::{GitReference, SourceId, Workspace};
 use cargo::ops;
 use cargo::util::IntoUrl;
 
+use cargo_util::paths;
+
 pub fn cli() -> App {
     subcommand("install")
         .about("Install a Rust binary. Default location is $HOME/.cargo/bin")
@@ -80,13 +82,20 @@ pub fn cli() -> App {
 }
 
 pub fn exec(config: &mut Config, args: &ArgMatches) -> CliResult {
-    if let Some(path) = args.value_of_path("path", config) {
+    let path = args.value_of_path("path", config);
+    if let Some(path) = &path {
         config.reload_rooted_at(path)?;
     } else {
         // TODO: Consider calling set_search_stop_path(home).
         config.reload_rooted_at(config.home().clone().into_path_unlocked())?;
     }
 
+    // In general, we try to avoid normalizing paths in Cargo,
+    // but in these particular cases we need it to fix rust-lang/cargo#10283.
+    // (Handle `SourceId::for_path` and `Workspace::new`,
+    // but not `Config::reload_rooted_at` which is always cwd)
+    let path = path.map(|p| paths::normalize_path(&p));
+
     let krates = args
         .values_of("crate")
         .unwrap_or_default()
@@ -106,7 +115,7 @@ pub fn exec(config: &mut Config, args: &ArgMatches) -> CliResult {
             GitReference::DefaultBranch
         };
         SourceId::for_git(&url, gitref)?
-    } else if let Some(path) = args.value_of_path("path", config) {
+    } else if let Some(path) = &path {
         SourceId::for_path(&path)?
     } else if krates.is_empty() {
         from_cwd = true;
@@ -125,9 +134,14 @@ pub fn exec(config: &mut Config, args: &ArgMatches) -> CliResult {
     // We only provide workspace information for local crate installation from
     // one of the following sources:
     // - From current working directory (only work for edition 2015).
-    // - From a specific local file path.
-    let workspace = if from_cwd || args.is_present("path") {
+    // - From a specific local file path (from `--path` arg).
+    //
+    // This workspace information is for emitting helpful messages from
+    // `ArgMatchesExt::compile_options` and won't affect the actual compilation.
+    let workspace = if from_cwd {
         args.workspace(config).ok()
+    } else if let Some(path) = &path {
+        Workspace::new(&path.join("Cargo.toml"), config).ok()
     } else {
         None
     };