feat: Add configurable functions path via SUPABASE_FUNCTIONS_PATH environment variable

[kshivang]

Problem

Currently, the edge-runtime has a hardcoded path for function compilation at /var/tmp/sb-compile-<executable-name>. This creates compatibility issues with deployment scenarios that require custom paths, particularly:

1. Kubernetes deployments using community Helm charts that mount functions at different paths (e.g., /home/deno/functions)
2. Restricted environments where /var/tmp may not be writable or available
3. Custom Docker deployments that prefer different directory structures

Solution

This PR adds a configurable SUPABASE_FUNCTIONS_PATH environment variable that allows users to override the default function compilation path while maintaining full backward compatibility.

Changes Made:

1. Modified standalone.rs: Added environment variable check for SUPABASE_FUNCTIONS_PATH with fallback to existing behavior
2. Updated README.md: Added documentation for the new environment variable
3. Maintained backward compatibility: Existing deployments continue to work unchanged

Code Changes:

let root_path = match std::env::var("SUPABASE_FUNCTIONS_PATH") {
  Ok(custom_path) => PathBuf::from(custom_path),
  Err(_) => {
    // Default behavior: use platform-specific temp directory
    if cfg!(target_family = "unix") {
      PathBuf::from("/var/tmp")
    } else {
      std::env::temp_dir()
    }
    .join(format!("sb-compile-{}", current_exe_name))
  }
};

Usage

Default behavior (unchanged):

• Unix/Linux: /var/tmp/sb-compile-edge-runtime
• Windows: %TEMP%\sb-compile-edge-runtime

Custom path:

export SUPABASE_FUNCTIONS_PATH=/home/deno/functions
./edge-runtime start --main-service /path/to/function

Kubernetes example:

env:
  - name: SUPABASE_FUNCTIONS_PATH
    value: "/home/deno/functions"

Testing

• ✅ Maintains backward compatibility (no environment variable set)
• ✅ Respects custom path when SUPABASE_FUNCTIONS_PATH is set
• ✅ Documentation updated

Benefits

1. Kubernetes compatibility: Enables edge functions to work with community Helm charts
2. Deployment flexibility: Allows custom paths for different deployment scenarios
3. Zero breaking changes: Existing deployments continue working without modification
4. Security: Enables deployment in environments with restricted /var/tmp access

Related Issues

• Addresses hardcoded path incompatibility reported in Edge Functions fail due to hardcoded path mismatch in edge-runtime supabase-community/supabase-kubernetes#117
• Enables edge functions support for community Kubernetes deployments

---

Reported-by: kshivang
Tested with: edge-runtime v1.69.6+

[kallebysantos]

May need to update this to not directly reference risashivang user.

[kallebysantos]

Hi @kshivang 💚
Is install_onnx.sh related with the main thread of this PR? or you just took the opportunity to refactor it as well?
May you please add a note of this change on your PR description? - for documenting

[kshivang]

sure I will

[kshivang]

Hey @kallebysantos I removed other commit from this PR, keeping just first commit that is relevant for this fix. For onnx I will create separate PR, as it is not relevant for this PR