Add patches to installer to support transition from cargo-home to flat install layouts

cargo-dist/templates/installer/installer.ps1.j2

@@ -302,6 +302,22 @@ function Invoke-Installer($artifacts, $platforms) {
     $install_layout = "flat"
   }
 
+  # Check if the install layout should be changed from `flat` to `cargo-home`
+  # for backwards compatible updates of applications that switched layouts.
+  if (($force_install_dir) -and ($install_layout -eq "flat")) {
+    # If the install directory is targeting the Cargo home directory, then
+    # we assume this application was previously installed that layout
+    # Note the installer passes the path with `\\` separators, but here they are
+    # `\` so we normalize for comparison. We don't use `Resolve-Path` because they
+    # may not exist.
+    $cargo_home = if ($env:CARGO_HOME) { $env:CARGO_HOME } else {
+        Join-Path $(if ($env:HOME) { $env:HOME } else { "" }) ".cargo"
+    }
+    if ($force_install_dir.Replace('\\', '\') -eq $cargo_home) {
+      $install_layout = "cargo-home"
+    }
+  }
+
   # The actual path we're going to install to
   $dest_dir = $null
   $dest_dir_lib = $null

cargo-dist/templates/installer/installer.sh.j2

@@ -461,6 +461,18 @@ install() {
         _install_layout="flat"
     fi
 
+    # Check if the install layout should be changed from `flat` to `cargo-home`
+    # for backwards compatible updates of applications that switched layouts.
+    if [ -n "${_force_install_dir:-}" ]; then
+        if [ "$_install_layout" = "flat" ]; then
+            # If the install directory is targeting the Cargo home directory, then
+            # we assume this application was previously installed that layout
+            if [ "$_force_install_dir" = "${CARGO_HOME:-${HOME:-}/.cargo}" ]; then
+                _install_layout="cargo-home"
+            fi
+        fi
+     fi
+
     # Before actually consulting the configured install strategy, see
     # if we're overriding it.
     if [ -n "${_force_install_dir:-}" ]; then