apphost does not respect DOTNET_ROOT

[mspielberg]

Describe the bug

Attempting to run an .NET Core app with the runtime installed to a non-default directory fails to find libhostfxr.so, as in #9304 / #12359. Unlike in those issues, the problem persists even with DOTNET_ROOT correctly set. Moving the installation to the default /usr/share/dotnet location resolves the error, so this seems to be a problem of the environment variable not being respected.

To Reproduce

❯ dotnet tool install ilspycmd --prerelease -g
You can invoke the tool using the following command: ilspycmd
Tool 'ilspycmd' (version '8.0.0.7106-preview2') was successfully installed.
❯ dotnet tool list -g
Package Id      Version                  Commands
-------------------------------------------------
ilspycmd        8.0.0.7106-preview2      ilspycmd
❯ dotnet --list-runtimes
Microsoft.AspNetCore.App 6.0.3 [/home/orion/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 6.0.3 [/home/orion/dotnet/shared/Microsoft.NETCore.App]
❯ export DOTNET_ROOT=/home/orion/dotnet
❯ echo $DOTNET_ROOT
/home/orion/dotnet
❯ ls -l $DOTNET_ROOT
total 188
-rw-r--r--    1 orion    orion         1116 Feb 23  2022 LICENSE.txt
-rw-r--r--    1 orion    orion        78479 Feb 23  2022 ThirdPartyNotices.txt
-rwxr-xr-x    1 orion    orion        76136 Feb 23  2022 dotnet
drwxr-sr-x    3 orion    orion         4096 Feb 24  2022 host
drwxr-sr-x    2 orion    orion         4096 Sep 29 23:45 metadata
drwxr-sr-x    6 orion    orion         4096 Feb 24  2022 packs
drwxr-sr-x    3 orion    orion         4096 Feb 24  2022 sdk
drwxr-sr-x    3 orion    orion         4096 Feb 24  2022 sdk-manifests
drwxr-sr-x    4 orion    orion         4096 Feb 24  2022 shared
drwxr-sr-x    3 orion    orion         4096 Feb 24  2022 templates
❯ ilspycmd
A fatal error occurred. The required library libhostfxr.so could not be found.
If this is a self-contained application, that library should exist in [/home/orion/.dotnet/tools/.store/ilspycmd/8.0.0.7106-preview2/ilspycmd/8.0.0.7106-preview2/tools/net6.0/any/].
If this is a framework-dependent application, install the runtime in the global location [/usr/share/dotnet] or use the DOTNET_ROOT environment variable to specify the runtime location or register the runtime location in [/etc/dotnet].

The .NET runtime can be found at:
  - https://aka.ms/dotnet-core-applaunch?missing_runtime=true&arch=x64&rid=alpine.3.15-x64&apphost_version=6.0.3
❯ sudo mv $DOTNET_ROOT /usr/share/dotnet
❯ ilspycmd
The Assembly file name(s) field is required.
Specify --help for a list of available options and commands.

Exceptions (if any)

(See error message above.)

Further technical details

• Include the output of dotnet --info

❯ dotnet --info
.NET SDK (reflecting any global.json):
 Version:   6.0.201
 Commit:    ef40e6aa06

Runtime Environment:
 OS Name:     alpine
 OS Version:  3.15
 OS Platform: Linux
 RID:         alpine.3.15-x64
 Base Path:   /home/orion/dotnet/sdk/6.0.201/

Host (useful for support):
  Version: 6.0.3
  Commit:  c24d9a9c91

.NET SDKs installed:
  6.0.201 [/home/orion/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.3 [/home/orion/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.3 [/home/orion/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download

• Note that updating to runtime 6.0.9 did not affect the issue at all:

❯ dotnet --info
.NET SDK (reflecting any global.json):
 Version:   6.0.401
 Commit:    0906eae6f8

Runtime Environment:
 OS Name:     alpine
 OS Version:  3.15
 OS Platform: Linux
 RID:         alpine.3.15-x64
 Base Path:   /home/orion/dotnet/sdk/6.0.401/

global.json file:
  Not found

Host:
  Version:      6.0.9
  Architecture: x64
  Commit:       163a63591c

.NET SDKs installed:
  6.0.401 [/home/orion/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.9 [/home/orion/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.9 [/home/orion/dotnet/shared/Microsoft.NETCore.App]

Download .NET:
  https://aka.ms/dotnet-download

Learn about .NET Runtimes and SDKs:
  https://aka.ms/dotnet/runtimes-sdk-info

[mspielberg]

Apologies. I discovered a forgotten shell alias defined that was changing the value of DOTNET_ROOT to an incorrect value. I discovered this by using COREHOST_TRACE=1, which may help other troubleshoot similar issues.