wip

src/Plugins/Tia/ChangedFiles.php

@@ -241,7 +241,20 @@ final readonly class ChangedFiles
             }
         }
 
-        return $this->gitOutput(['git', 'config', '--get', 'init.defaultBranch']);
+        // `init.defaultBranch` is a setting of the machine, not of the
+        // repository — it names what `git init` would have called the first
+        // branch here, which is worth nothing once the repository disagrees.
+        // Taken only when a branch by that name actually exists.
+        $configured = $this->gitOutput(['git', 'config', '--get', 'init.defaultBranch']);
+
+        if ($configured === null) {
+            return null;
+        }
+
+        $exists = $this->gitOutput(['git', 'rev-parse', '--verify', '--quiet', 'refs/heads/'.$configured]) !== null
+            || $this->gitOutput(['git', 'rev-parse', '--verify', '--quiet', 'refs/remotes/origin/'.$configured]) !== null;
+
+        return $exists ? $configured : null;
     }
 
     /**

src/Plugins/Tia/CiDefaultBranch.php

@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Plugins\Tia;
+
+/**
+ * The default branch as the CI provider itself reports it.
+ *
+ * Worth asking before git: a CI checkout is the one place where git knows the
+ * least. `actions/checkout` builds the working copy with `git init` plus a
+ * single-ref `fetch` rather than a `clone`, so `origin/HEAD` is never set and
+ * `init.defaultBranch` — a setting of the runner image, not of the repository —
+ * is all git has left to offer. The provider, meanwhile, states the answer
+ * outright in the environment it handed us.
+ *
+ * @internal
+ */
+final class CiDefaultBranch
+{
+    /**
+     * Advisory, like every other source in the chain: anything unreadable,
+     * unparsable, or simply absent means "no answer", never a failure.
+     */
+    public static function detect(): ?string
+    {
+        return self::fromGitLab() ?? self::fromGitHubEvent();
+    }
+
+    private static function fromGitLab(): ?string
+    {
+        return self::environment('CI_DEFAULT_BRANCH');
+    }
+
+    /**
+     * GitHub publishes no default-branch variable, but every repository-scoped
+     * event payload carries `repository.default_branch`, and the path to that
+     * payload is in the environment.
+     */
+    private static function fromGitHubEvent(): ?string
+    {
+        $path = self::environment('GITHUB_EVENT_PATH');
+
+        if ($path === null || ! is_file($path) || ! is_readable($path)) {
+            return null;
+        }
+
+        $contents = @file_get_contents($path);
+
+        if ($contents === false) {
+            return null;
+        }
+
+        $payload = json_decode($contents, true);
+
+        if (! is_array($payload) || ! is_array($payload['repository'] ?? null)) {
+            return null;
+        }
+
+        $branch = $payload['repository']['default_branch'] ?? null;
+
+        return is_string($branch) && $branch !== '' ? $branch : null;
+    }
+
+    private static function environment(string $name): ?string
+    {
+        $value = getenv($name);
+
+        if (! is_string($value)) {
+            return null;
+        }
+
+        $value = trim($value);
+
+        return $value === '' ? null : $value;
+    }
+}

src/Plugins/Tia/Graph.php

@@ -1482,6 +1482,35 @@ final class Graph
         }
     }
 
+    /**
+     * The branches a recorded graph holds baselines for, read straight from the
+     * encoded form.
+     *
+     * Answerable before the graph is hydrated because the default branch has to
+     * be resolved first: the fallback is what every hydrated graph reads its
+     * baselines through.
+     *
+     * @return list<string>
+     */
+    public static function branchesIn(string $json): array
+    {
+        $data = json_decode($json, true);
+
+        if (! is_array($data) || ! is_array($data['baselines'] ?? null)) {
+            return [];
+        }
+
+        $branches = [];
+
+        foreach (array_keys($data['baselines']) as $branch) {
+            if (is_string($branch) && $branch !== '') {
+                $branches[] = $branch;
+            }
+        }
+
+        return $branches;
+    }
+
     public static function decode(string $json, string $projectRoot): ?self
     {
         $data = json_decode($json, true);