Always prepend to PATH instead of replacing it (microsoft#21906)

For microsoft#20822 microsoft#11039

Replacing as-is has its problems, for eg. pyenv asks their users to
manipulate `PATH` in their init script:
https://github.com/pyenv/pyenv#set-up-your-shell-environment-for-pyenv,
which we could end up replacing.


![image](https://github.com/microsoft/vscode-python/assets/13199757/cc904f76-8d42-47e1-a6c8-6cfff6543db8)

Particularly for pyenv, it mean users not being able to find pyenv:


![image](https://github.com/microsoft/vscode-python/assets/13199757/26100328-c227-435b-a4f2-ec168099f4c1)

Prepending solves it for cases where initial PATH value is suffix of the
final value:


![image](https://github.com/microsoft/vscode-python/assets/13199757/a95e4ffd-68dc-4e73-905e-504b3051324f)

But, in other cases, this means that we end up with the whole `PATH`
thrice. This is because it prepends it twice:
- Once in shell integration script
- Once when creating a process

So the final value could be:
```
PATH=<activated_full_path><activated_full_path><original_path>
```
where `<activated_full_path>` refers to value of `PATH` environment
variable post activation. eg.


![image](https://github.com/microsoft/vscode-python/assets/13199757/7e771f62-eb53-49be-b261-d259096008f3)

src/client/interpreter/activation/terminalEnvVarCollectionService.ts

@@ -167,7 +167,7 @@ export class TerminalEnvVarCollectionService implements IExtensionActivationServ
  if (shouldSkip(key)) {
  return;
  }
- const value = env[key];
+ let value = env[key];
  const prevValue = processEnv[key];
  if (prevValue !== value) {
  if (value !== undefined) {
@@ -180,6 +180,26 @@ export class TerminalEnvVarCollectionService implements IExtensionActivationServ
  });
  return;
  }
+ if (key === 'PATH') {
+ if (processEnv.PATH && env.PATH?.endsWith(processEnv.PATH)) {
+ // Prefer prepending to PATH instead of replacing it, as we do not want to replace any
+ // changes to PATH users might have made it in their init scripts (~/.bashrc etc.)
+ const prependedPart = env.PATH.slice(0, -processEnv.PATH.length);
+ value = prependedPart;
+ traceVerbose(`Prepending environment variable ${key} in collection with ${value}`);
+ envVarCollection.prepend(key, value, {
+ applyAtShellIntegration: true,
+ applyAtProcessCreation: true,
+ });
+ } else {
+ traceVerbose(`Prepending environment variable ${key} in collection to ${value}`);
+ envVarCollection.prepend(key, value, {
+ applyAtShellIntegration: true,
+ applyAtProcessCreation: true,
+ });
+ }
+ return;
+ }
  traceVerbose(`Setting environment variable ${key} in collection to ${value}`);
  envVarCollection.replace(key, value, {
  applyAtShellIntegration: true,

src/test/interpreters/activation/terminalEnvVarCollectionService.unit.test.ts

@@ -216,6 +216,70 @@ suite('Terminal Environment Variable Collection Service', () => {
  assert.deepEqual(opts, { applyAtProcessCreation: false, applyAtShellIntegration: true });
  });
 
+ test('Prepend only "prepend portion of PATH" where applicable', async () => {
+ const processEnv = { PATH: 'hello/1/2/3' };
+ reset(environmentActivationService);
+ when(environmentActivationService.getProcessEnvironmentVariables(anything(), anything())).thenResolve(
+ processEnv,
+ );
+ const prependedPart = 'path/to/activate/dir:';
+ const envVars: NodeJS.ProcessEnv = { PATH: `${prependedPart}${processEnv.PATH}` };
+ when(
+ environmentActivationService.getActivatedEnvironmentVariables(
+ anything(),
+ undefined,
+ undefined,
+ customShell,
+ ),
+ ).thenResolve(envVars);
+
+ when(collection.replace(anything(), anything(), anything())).thenResolve();
+ when(collection.delete(anything())).thenResolve();
+ let opts: EnvironmentVariableMutatorOptions | undefined;
+ when(collection.prepend('PATH', anything(), anything())).thenCall((_, _v, o) => {
+ opts = o;
+ });
+
+ await terminalEnvVarCollectionService._applyCollection(undefined, customShell);
+
+ verify(collection.clear()).once();
+ verify(collection.prepend('PATH', prependedPart, anything())).once();
+ verify(collection.replace('PATH', anything(), anything())).never();
+ assert.deepEqual(opts, { applyAtProcessCreation: true, applyAtShellIntegration: true });
+ });
+
+ test('Prepend full PATH otherwise', async () => {
+ const processEnv = { PATH: 'hello/1/2/3' };
+ reset(environmentActivationService);
+ when(environmentActivationService.getProcessEnvironmentVariables(anything(), anything())).thenResolve(
+ processEnv,
+ );
+ const finalPath = 'hello/3/2/1';
+ const envVars: NodeJS.ProcessEnv = { PATH: finalPath };
+ when(
+ environmentActivationService.getActivatedEnvironmentVariables(
+ anything(),
+ undefined,
+ undefined,
+ customShell,
+ ),
+ ).thenResolve(envVars);
+
+ when(collection.replace(anything(), anything(), anything())).thenResolve();
+ when(collection.delete(anything())).thenResolve();
+ let opts: EnvironmentVariableMutatorOptions | undefined;
+ when(collection.prepend('PATH', anything(), anything())).thenCall((_, _v, o) => {
+ opts = o;
+ });
+
+ await terminalEnvVarCollectionService._applyCollection(undefined, customShell);
+
+ verify(collection.clear()).once();
+ verify(collection.prepend('PATH', finalPath, anything())).once();
+ verify(collection.replace('PATH', anything(), anything())).never();
+ assert.deepEqual(opts, { applyAtProcessCreation: true, applyAtShellIntegration: true });
+ });
+
  test('Verify envs are not applied if env activation is disabled', async () => {
  const envVars: NodeJS.ProcessEnv = { CONDA_PREFIX: 'prefix/to/conda', ...process.env };
  when(