From e90e4f70fcc4f5afce03dd1050f715dd8c218586 Mon Sep 17 00:00:00 2001
From: nuno maduro <enunomaduro@gmail.com>
Date: Wed, 5 Aug 2026 20:20:35 +0100
Subject: [PATCH] wip

---
 src/Exceptions/TiaRequiresDefaultBranch.php   |  52 ++++++++
 src/Plugins/Tia.php                           |  71 +++++++++--
 src/Plugins/Tia/ChangedFiles.php              |  15 ++-
 src/Plugins/Tia/CiDefaultBranch.php           |  77 ++++++++++++
 src/Plugins/Tia/Graph.php                     |  29 +++++
 .../Features/Tia/DefaultBranchResolution.php  | 114 +++++++++++++++++-
 tests/Fixtures/Tia/GitRepo.php                |  11 ++
 tests/Fixtures/Tia/Project.php                |   7 ++
 8 files changed, 360 insertions(+), 16 deletions(-)
 create mode 100644 src/Exceptions/TiaRequiresDefaultBranch.php
 create mode 100644 src/Plugins/Tia/CiDefaultBranch.php

diff --git a/src/Exceptions/TiaRequiresDefaultBranch.php b/src/Exceptions/TiaRequiresDefaultBranch.php
new file mode 100644
index 00000000..d914d26b
--- /dev/null
+++ b/src/Exceptions/TiaRequiresDefaultBranch.php
@@ -0,0 +1,52 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Exceptions;
+
+use NunoMaduro\Collision\Contracts\RenderlessEditor;
+use NunoMaduro\Collision\Contracts\RenderlessTrace;
+use Pest\Contracts\Panicable;
+use RuntimeException;
+use Symfony\Component\Console\Exception\ExceptionInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * @internal
+ */
+final class TiaRequiresDefaultBranch extends RuntimeException implements ExceptionInterface, Panicable, RenderlessEditor, RenderlessTrace
+{
+    public function __construct()
+    {
+        parent::__construct(
+            'Tia mode could not determine the default branch every other branch falls back to reading.',
+        );
+    }
+
+    public function render(OutputInterface $output): void
+    {
+        $output->writeln([
+            '',
+            '  <fg=white;options=bold;bg=red> ERROR </> Tia mode could not determine the default branch.',
+            '',
+            '  It is the branch whose baseline every other branch falls back to reading, and',
+            '  nothing in this checkout names it: the repository has a remote, but no',
+            '  <fg=yellow>origin/HEAD</>, and no CI provider stated it either. Guessing would re-run the',
+            '  whole suite on every new branch while reporting it as a cache hit.',
+            '',
+            '  Name the branch in <fg=yellow>tests/Pest.php</>:',
+            '',
+            '    <fg=yellow>pest()->tia()->defaultBranch(\'master\');</>',
+            '',
+            '  Or let git answer, once per clone:',
+            '',
+            '    <fg=yellow>git remote set-head origin --auto</>',
+            '',
+        ]);
+    }
+
+    public function exitCode(): int
+    {
+        return 1;
+    }
+}
diff --git a/src/Plugins/Tia.php b/src/Plugins/Tia.php
index 97e5e791..3032be6c 100644
--- a/src/Plugins/Tia.php
+++ b/src/Plugins/Tia.php
@@ -12,12 +12,14 @@ use Pest\Contracts\Plugins\Terminable;
 use Pest\Exceptions\InvalidOption;
 use Pest\Exceptions\MissingDependency;
 use Pest\Exceptions\NoAffectedTestsFound;
+use Pest\Exceptions\TiaRequiresDefaultBranch;
 use Pest\Exceptions\TiaRequiresRemote;
 use Pest\Exceptions\TiaRequiresRepositoryRoot;
 use Pest\Panic;
 use Pest\Plugins\Concerns\HandleArguments;
 use Pest\Plugins\Tia\BaselineSync;
 use Pest\Plugins\Tia\ChangedFiles;
+use Pest\Plugins\Tia\CiDefaultBranch;
 use Pest\Plugins\Tia\Contracts\State;
 use Pest\Plugins\Tia\CoverageCollector;
 use Pest\Plugins\Tia\Fingerprint;
@@ -244,6 +246,16 @@ final class Tia implements AddsOutput, HandlesArguments, HandlesOriginalArgument
      */
     private string $fallbackBranch = self::DEFAULT_BRANCH;
 
+    /**
+     * Whether anything actually named the branch above.
+     *
+     * When nothing did, the value is a guess, and a guess is what the TIA path
+     * refuses to run on: an unresolved fallback reads no baseline at all, which
+     * looks exactly like a hit in the output. Runs that never asked for TIA
+     * still have to write somewhere, so the guess stands for them.
+     */
+    private bool $fallbackBranchResolved = false;
+
     private bool $branchResolved = false;
 
     /** @var array<string, true> */
@@ -889,11 +901,15 @@ final class Tia implements AddsOutput, HandlesArguments, HandlesOriginalArgument
         $this->resolveBranch($projectRoot);
 
         // After resolveBranch(), so a directory that is no repository at all
-        // still reports the missing git dependency rather than a missing remote.
-        // Skipped once the default branch is configured by hand: there is then
-        // nothing left for a remote to answer.
-        if ($this->watchPatterns->defaultBranch() === null && ! new ChangedFiles($projectRoot)->hasRemote()) {
-            Panic::with(new TiaRequiresRemote);
+        // still reports the missing git dependency rather than an unresolved
+        // default branch. Nothing named the branch every other baseline reads
+        // through, so every new branch would re-run the whole suite while the
+        // output called it a hit. A repository with no remote is the likeliest
+        // reason and gets said out loud.
+        if (! $this->fallbackBranchResolved) {
+            Panic::with(new ChangedFiles($projectRoot)->hasRemote()
+                ? new TiaRequiresDefaultBranch
+                : new TiaRequiresRemote);
         }
 
         $fingerprint = Fingerprint::compute($projectRoot);
@@ -2001,7 +2017,10 @@ final class Tia implements AddsOutput, HandlesArguments, HandlesOriginalArgument
         // Resolved before the current branch, which throws where git is
         // missing: the fallback is advisory, so a run that cannot name its
         // branch at all should still carry the best answer available.
-        $this->fallbackBranch = $this->resolveFallbackBranch($changedFiles);
+        $resolved = $this->resolveFallbackBranch($changedFiles);
+
+        $this->fallbackBranchResolved = $resolved !== null;
+        $this->fallbackBranch = $resolved ?? self::DEFAULT_BRANCH;
 
         Parallel::setGlobal(self::FALLBACK_BRANCH_GLOBAL, $this->fallbackBranch);
 
@@ -2012,7 +2031,18 @@ final class Tia implements AddsOutput, HandlesArguments, HandlesOriginalArgument
         $this->branch = $changedFiles->currentBranch() ?? $this->fallbackBranch;
     }
 
-    private function resolveFallbackBranch(ChangedFiles $changedFiles): string
+    /**
+     * The branch every other baseline falls back to reading, or null when
+     * nothing in the checkout can name it.
+     *
+     * Ordered by how much the source actually knows. Configuration first: it is
+     * the escape hatch for a repository whose git-side answers disagree with its
+     * branches. Then the CI provider, which states the answer outright where git
+     * is at its least informed. Then git itself. Then the recorded graph, whose
+     * single baseline can only have come from the branch this repository
+     * integrates on.
+     */
+    private function resolveFallbackBranch(ChangedFiles $changedFiles): ?string
     {
         $inherited = Parallel::getGlobal(self::FALLBACK_BRANCH_GLOBAL);
 
@@ -2020,12 +2050,31 @@ final class Tia implements AddsOutput, HandlesArguments, HandlesOriginalArgument
             return $inherited;
         }
 
-        // Configuration wins over autodetection: it is the escape hatch for a
-        // repository whose `origin/HEAD` is unset and whose `init.defaultBranch`
-        // says something else than its branches do.
         return $this->watchPatterns->defaultBranch()
+            ?? CiDefaultBranch::detect()
             ?? $changedFiles->defaultBranch()
-            ?? self::DEFAULT_BRANCH;
+            ?? $this->soleRecordedBranch();
+    }
+
+    /**
+     * The one branch a recorded graph holds a baseline for.
+     *
+     * Last in the chain and deliberately narrow: with a single baseline on disk
+     * there is only one branch whose results can be read at all, so naming it is
+     * strictly better than resolving to a branch that holds nothing. Two or more
+     * baselines carry no such implication and are left alone.
+     */
+    private function soleRecordedBranch(): ?string
+    {
+        $json = $this->state->read(self::KEY_GRAPH);
+
+        if ($json === null) {
+            return null;
+        }
+
+        $branches = Graph::branchesIn($json);
+
+        return count($branches) === 1 ? $branches[0] : null;
     }
 
     /**
diff --git a/src/Plugins/Tia/ChangedFiles.php b/src/Plugins/Tia/ChangedFiles.php
index 979eba48..9207bd03 100644
--- a/src/Plugins/Tia/ChangedFiles.php
+++ b/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;
     }
 
     /**
diff --git a/src/Plugins/Tia/CiDefaultBranch.php b/src/Plugins/Tia/CiDefaultBranch.php
new file mode 100644
index 00000000..07450ae3
--- /dev/null
+++ b/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;
+    }
+}
diff --git a/src/Plugins/Tia/Graph.php b/src/Plugins/Tia/Graph.php
index 83806b53..22f42f7d 100644
--- a/src/Plugins/Tia/Graph.php
+++ b/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);
diff --git a/tests/Features/Tia/DefaultBranchResolution.php b/tests/Features/Tia/DefaultBranchResolution.php
index e80fd29d..a79a350f 100644
--- a/tests/Features/Tia/DefaultBranchResolution.php
+++ b/tests/Features/Tia/DefaultBranchResolution.php
@@ -42,9 +42,117 @@ test('a declared default branch that does not exist degrades to a full run', fun
         ->and($project->branchKeys())->toBe(['master', 'feature-x']);
 })->skipOnWindows();
 
+test('the CI provider names the default branch where the checkout cannot', function (): void {
+    // A CI checkout: `actions/checkout` fetches a single ref instead of cloning,
+    // so there is no `origin/HEAD` for git to read the default branch from. The
+    // event payload GitHub hands the job says it outright.
+    $project = Project::make('master');
+    $project->git()->unsetOriginHead();
+    $project->seed('master');
+
+    $project->git()->switchTo('feature-x', new: true);
+
+    $project->write('.home/event.json', (string) json_encode([
+        'repository' => ['default_branch' => 'master'],
+    ]));
+
+    $result = $project->pestWithEnvironment($project->path(), [
+        'GITHUB_EVENT_PATH' => $project->path('.home/event.json'),
+    ], '--tia');
+
+    expect($result->replayed())->toBe(Project::TOTAL_TESTS, $result->describe())
+        ->and($result->uncached())->toBe(0, $result->describe());
+})->skipOnWindows();
+
+test('GitLab names the default branch through its own variable', function (): void {
+    $project = Project::make('master');
+    $project->git()->unsetOriginHead();
+    $project->seed('master');
+
+    $project->git()->switchTo('feature-x', new: true);
+
+    $result = $project->pestWithEnvironment($project->path(), [
+        'CI_DEFAULT_BRANCH' => 'master',
+    ], '--tia');
+
+    expect($result->replayed())->toBe(Project::TOTAL_TESTS, $result->describe())
+        ->and($result->uncached())->toBe(0, $result->describe());
+})->skipOnWindows();
+
+test('a lone recorded baseline names the default branch', function (): void {
+    // Nothing left to ask: no `origin/HEAD`, no CI provider, and an
+    // `init.defaultBranch` that names a branch this repository does not have.
+    // The graph holds exactly one baseline, and it is the only one any branch
+    // could read — so it is the answer.
+    $project = Project::make('master');
+    $project->git()->unsetOriginHead();
+    $project->git()->config('init.defaultBranch', 'main');
+    $project->seed('master');
+
+    $project->git()->switchTo('feature-x', new: true);
+
+    $result = $project->pest('--tia');
+
+    expect($result->replayed())->toBe(Project::TOTAL_TESTS, $result->describe())
+        ->and($result->uncached())->toBe(0, $result->describe());
+})->skipOnWindows();
+
+test('a default branch nothing can name is refused rather than guessed', function (): void {
+    // Same checkout as above, without the graph that answered it. Guessing here
+    // is what made this bug expensive: the guess reads no baseline at all, and
+    // the output calls that a hit.
+    $project = Project::make('master');
+    $project->git()->unsetOriginHead();
+    $project->git()->config('init.defaultBranch', 'main');
+
+    $project->git()->switchTo('feature-x', new: true);
+
+    $result = $project->pest('--tia');
+
+    expect($result->output)->toContain('Tia mode could not determine the default branch.')
+        ->and($result->output)->toContain('git remote set-head origin --auto')
+        ->and($result->exitCode)->toBe(1, $result->describe())
+        ->and($project->graphExists())->toBeFalse();
+})->skipOnWindows();
+
+test('an init.defaultBranch naming a branch that exists is still trusted', function (): void {
+    // The setting is the machine's, not the repository's — worth taking only
+    // where the repository has a branch by that name. It does here, and with no
+    // graph on disk it is the only source left, so the run must not be refused.
+    $project = Project::make('master');
+    $project->git()->unsetOriginHead();
+    $project->git()->config('init.defaultBranch', 'master');
+
+    $project->git()->switchTo('feature-x', new: true);
+
+    $result = $project->pest('--tia');
+
+    expect($result->exitCode)->toBe(0, $result->describe())
+        ->and($result->output)->not->toContain('could not determine the default branch')
+        ->and($project->branchKeys())->toBe(['feature-x']);
+})->skipOnWindows();
+
 test('a repository with no remote is refused rather than silently re-run', function (): void {
     $project = Project::make('master');
 
+    $project->git()->removeOrigin();
+
+    $project->git()->switchTo('feature-x', new: true);
+
+    $result = $project->pest('--tia');
+
+    // Nothing can name the default branch, so every new branch would re-run the
+    // whole suite with no explanation. Saying so beats doing that quietly. The
+    // missing remote is the likeliest reason and gets named as such.
+    expect($result->output)->toContain('Tia mode requires a repository with a remote.')
+        ->and($result->exitCode)->toBe(1, $result->describe());
+})->skipOnWindows();
+
+test('a remote-less repository holding one baseline is not refused', function (): void {
+    // The refusal above exists to stop a guess, not to demand a remote for its
+    // own sake. With a baseline on disk there is nothing left to guess at.
+    $project = Project::make('master');
+
     $project->git()->removeOrigin();
     $project->seed('master');
 
@@ -52,10 +160,8 @@ test('a repository with no remote is refused rather than silently re-run', funct
 
     $result = $project->pest('--tia');
 
-    // Nothing can name the default branch, so every new branch would re-run the
-    // whole suite with no explanation. Saying so beats doing that quietly.
-    expect($result->output)->toContain('Tia mode requires a repository with a remote.')
-        ->and($result->exitCode)->toBe(1, $result->describe());
+    expect($result->replayed())->toBe(Project::TOTAL_TESTS, $result->describe())
+        ->and($result->uncached())->toBe(0, $result->describe());
 })->skipOnWindows();
 
 test('a declared default branch stands in for a missing remote', function (): void {
diff --git a/tests/Fixtures/Tia/GitRepo.php b/tests/Fixtures/Tia/GitRepo.php
index 18c4689e..e828fd04 100644
--- a/tests/Fixtures/Tia/GitRepo.php
+++ b/tests/Fixtures/Tia/GitRepo.php
@@ -96,6 +96,17 @@ final readonly class GitRepo
         $this->run(['symbolic-ref', 'refs/remotes/origin/HEAD', 'refs/remotes/origin/'.$branch]);
     }
 
+    /**
+     * Drops `refs/remotes/origin/HEAD` while keeping the remote-tracking branch
+     * — what a CI checkout looks like. `actions/checkout` builds its working
+     * copy with `git init` plus a single-ref `fetch` rather than a `clone`, and
+     * only a `clone` writes that symbolic ref.
+     */
+    public function unsetOriginHead(): void
+    {
+        $this->run(['symbolic-ref', '--delete', 'refs/remotes/origin/HEAD']);
+    }
+
     public function config(string $key, string $value): void
     {
         $this->run(['config', '--local', $key, $value]);
diff --git a/tests/Fixtures/Tia/Project.php b/tests/Fixtures/Tia/Project.php
index 67443f43..ee6b42ff 100644
--- a/tests/Fixtures/Tia/Project.php
+++ b/tests/Fixtures/Tia/Project.php
@@ -222,6 +222,13 @@ final class Project
                 'PARATEST' => '0',
                 'PAO_DISABLE' => '1',
                 'HOME' => $this->home(),
+                // Blanked for the same reason `GitRepo::ENV` blanks git's own
+                // config: the default branch a CI provider reports is the one
+                // *its* build is for. Pest's suite runs on GitHub Actions, so
+                // without this every scenario would autodetect Pest's default
+                // branch instead of the fixture's.
+                'GITHUB_EVENT_PATH' => '',
+                'CI_DEFAULT_BRANCH' => '',
                 ...$environment,
             ],
         );