fix(manager/composer): respect the PHP override in composer.json

lib/manager/composer/types.ts

@@ -8,6 +8,11 @@ export interface Repo {
 }
 export interface ComposerConfig {
   type?: string;
+  config?: {
+    platform?: {
+      php?: string;
+    };
+  };
   /**
    * A repositories field can be an array of Repo objects or an object of repoName: Repo
    * Also it can be a boolean (usually false) to disable packagist.

lib/manager/composer/utils.spec.ts

@@ -18,6 +18,18 @@ describe('manager/composer/utils', () => {
       ).toEqual({ php: '>=5.3.2', composer: '1.1.0' });
     });
 
+    it('returns platform php version', () => {
+      expect(
+        extractContraints(
+          {
+            config: { platform: { php: '7.4.27' } },
+            require: { php: '~7.4 || ~8.0' },
+          },
+          {}
+        )
+      ).toEqual({ php: '7.4.27' });
+    });
+
     it('returns from require-dev', () => {
       expect(
         extractContraints(

lib/manager/composer/utils.ts

@@ -69,7 +69,9 @@ export function extractContraints(
   const res: Record<string, string> = { composer: '1.*' };
 
   // extract php
-  if (composerJson.require?.php) {
+  if (composerJson.config?.platform?.php) {
+    res.php = composerJson.config?.platform?.php;
+  } else if (composerJson.require?.php) {
     res.php = composerJson.require?.php;
   }