fix(service): store the Compose default for bare variable references

Closes #12412

bootstrap/helpers/parsers.php

@@ -2422,6 +2422,7 @@ function serviceParser(Service $resource): Collection
                 ->orWhere('key', 'LIKE', '%}');
         })
         ->delete();
+    $existingEnvironmentVariableKeys = $resource->environment_variables()->pluck('key');
 
     $topLevel = collect([
         'volumes' => collect(data_get($yaml, 'volumes', [])),
@@ -3671,6 +3672,7 @@ function serviceParser(Service $resource): Collection
     data_forget($resource, 'environment_variables_preview');
     $resource->save();
 
+    fillDockerComposeDefaultsForBareReferences($resource, $existingEnvironmentVariableKeys);
     syncDockerComposeEnvironmentVariableRequiredState($resource);
 
     return $topLevel;

bootstrap/helpers/shared.php

@@ -5580,6 +5580,63 @@ function dockerComposeEnvironmentVariableInfo(?string $dockerCompose, string $ke
     ];
 }
 
+/**
+ * Docker Compose gives a bare $VAR or ${VAR} reference no default, and the service parser does not store
+ * defaults. So `/$POSTGRES_DB` next to `${POSTGRES_DB:-umami}` in another service resolves to an empty value.
+ * For new variables, store the default when the Compose file has a bare reference and exactly one default.
+ *
+ * @param  Collection<int, string>  $existingKeys
+ */
+function fillDockerComposeDefaultsForBareReferences(Service $resource, Collection $existingKeys): void
+{
+    $dockerCompose = $resource->docker_compose_raw;
+    if (blank($dockerCompose)) {
+        return;
+    }
+
+    $resource->environment_variables()
+        ->whereNull('value')
+        ->whereNotIn('key', $existingKeys)
+        ->get()
+        ->each(function (EnvironmentVariable $environmentVariable) use ($dockerCompose): void {
+            $default = dockerComposeBareReferenceDefault($dockerCompose, $environmentVariable->key);
+            // A nested default (`${A:-${B}}`) must stay with Compose: stored, it would be escaped to a literal.
+            if (filled($default) && ! str_contains($default, '$')) {
+                $environmentVariable->update(['value' => $default]);
+            }
+        });
+}
+
+/** The single default of a variable that the Compose file also references without a default, otherwise null. */
+function dockerComposeBareReferenceDefault(string $dockerCompose, string $key): ?string
+{
+    $quotedKey = preg_quote($key, '/');
+    if (preg_match('/(?<!\$)\$(?:'.$quotedKey.'(?![A-Za-z0-9_])|\{'.$quotedKey.'\})/', $dockerCompose) !== 1) {
+        return null;
+    }
+
+    $defaults = [];
+    $offset = 0;
+    while (($referenceStart = strpos($dockerCompose, '${'.$key, $offset)) !== false) {
+        $offset = $referenceStart + 2;
+        if ($referenceStart > 0 && $dockerCompose[$referenceStart - 1] === '$') {
+            continue;
+        }
+
+        $reference = extractBalancedBraceContent(substr($dockerCompose, $referenceStart));
+        $split = $reference === null ? null : splitOnOperatorOutsideNested($reference['content']);
+        if ($split === null || $split['variable'] !== $key) {
+            continue;
+        }
+        if (str_contains($split['operator'], '?')) {
+            return null;
+        }
+        $defaults[$split['default']] = true;
+    }
+
+    return count($defaults) === 1 ? (string) array_key_first($defaults) : null;
+}
+
 function dockerComposeEnvironmentVariableIsRequired(?string $dockerCompose, string $key): bool
 {
     if (blank($dockerCompose)) {

tests/Feature/EnvironmentVariableSearchTest.php

@@ -396,6 +396,45 @@ YAML;
         ->and(Yaml::parse($service->fresh()->docker_compose_raw))->toBe(Yaml::parse($dockerCompose));
 });
 
+it('stores the Compose default for a variable that another service references without one', function (string $dockerCompose) {
+    $service = Service::factory()->create([
+        'environment_id' => $this->environment->id,
+        'server_id' => Server::factory()->create(['team_id' => $this->team->id])->id,
+        'docker_compose_raw' => $dockerCompose,
+    ]);
+
+    $service->parse();
+
+    expect($service->environment_variables()->where('key', 'POSTGRES_DB')->value('value'))->toBe('umami');
+})->with([
+    'reference before default' => "services:\n  app:\n    image: nginx\n    environment:\n      DATABASE_URL: postgres://user:pass@postgresql:5432/\$POSTGRES_DB\n  postgresql:\n    image: postgres:16-alpine\n    environment:\n      POSTGRES_DB: \${POSTGRES_DB:-umami}\n",
+    'default before reference' => "services:\n  postgresql:\n    image: postgres:16-alpine\n    environment:\n      POSTGRES_DB: \${POSTGRES_DB:-umami}\n  app:\n    image: nginx\n    environment:\n      DATABASE_URL: postgres://user:pass@postgresql:5432/\${POSTGRES_DB}\n",
+]);
+
+it('does not store a nested Compose default for a bare reference', function () {
+    $service = Service::factory()->create([
+        'environment_id' => $this->environment->id,
+        'server_id' => Server::factory()->create(['team_id' => $this->team->id])->id,
+        'docker_compose_raw' => "services:\n  app:\n    image: alpine\n    environment:\n      DB: \${DB:-\${APP_NAME}}\n      URL: postgres://db/\$DB\n",
+    ]);
+
+    $service->parse();
+
+    expect($service->environment_variables()->where('key', 'DB')->firstOrFail()->value)->toBeNull();
+});
+
+it('does not store a Compose default when the defaults for a bare reference conflict', function () {
+    $service = Service::factory()->create([
+        'environment_id' => $this->environment->id,
+        'server_id' => Server::factory()->create(['team_id' => $this->team->id])->id,
+        'docker_compose_raw' => "services:\n  app:\n    image: alpine\n    environment:\n      LEVEL: \${LEVEL:-info}\n      LOG: level=\$LEVEL\n  worker:\n    image: alpine\n    environment:\n      LEVEL: \${LEVEL:-warn}\n",
+    ]);
+
+    $service->parse();
+
+    expect($service->environment_variables()->where('key', 'LEVEL')->firstOrFail()->value)->toBeNull();
+});
+
 it('keeps editable and literal rows when services use the same key differently', function () {
     $service = Service::factory()->create([
         'environment_id' => $this->environment->id,