Ask for last good commit in bisect level

app/build.gradle.kts

@@ -19,8 +19,8 @@ android {
         applicationId = "solutions.tretter.githugandroid"
         minSdk = 26
         targetSdk = 35
-        versionCode = 152
-        versionName = "0.1.151"
+        versionCode = 153
+        versionName = "0.1.152"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
         vectorDrawables.useSupportLibrary = true

app/src/main/java/solutions/tretter/githugandroid/GitRuntime.kt

@@ -584,8 +584,8 @@ class GitRepositoryRuntime private constructor(
 
     private fun materializeNativeGitState(nativeGit: File, sandbox: File, desired: RepoState, level: Level) {
         level.nativeSetup?.let { setup ->
-            val nativeSetup = NativeLevelSetup(sandbox) { directory, arguments ->
-                runGit(nativeGit, directory, arguments).exitCode
+            val nativeSetup = NativeLevelSetup(sandbox) { directory, arguments, environment ->
+                runGit(nativeGit, directory, arguments, environment).exitCode
             }
             if (nativeSetup.setup()) {
                 return

app/src/main/java/solutions/tretter/githugandroid/NativeLevelSetup.kt

@@ -4,8 +4,10 @@ import java.io.File
 
 class NativeLevelSetup internal constructor(
     internal val sandbox: File,
-    private val runGit: (File, List<String>) -> Int,
+    private val runGit: (File, List<String>, Map<String, String>) -> Int,
 ) {
+    private var commitSequence = 0
+
     fun resetFiles() {
         sandbox.listFiles()
             ?.filterNot { it.name == ".git" }
@@ -13,9 +15,9 @@ class NativeLevelSetup internal constructor(
         git("checkout", "-B", "master")
     }
 
-    fun git(vararg arguments: String): Int = runGit(sandbox, arguments.toList())
+    fun git(vararg arguments: String): Int = runGit(sandbox, arguments.toList(), emptyMap())
 
-    fun git(directory: File, vararg arguments: String): Int = runGit(directory, arguments.toList())
+    fun git(directory: File, vararg arguments: String): Int = runGit(directory, arguments.toList(), emptyMap())
 
     fun initRepo(directory: File) {
         directory.mkdirs()
@@ -43,10 +45,15 @@ class NativeLevelSetup internal constructor(
     }
 
     fun commit(message: String, author: String? = null) {
+        val commitDate = nextDeterministicCommitDate()
+        val environment = mapOf(
+            "GIT_AUTHOR_DATE" to commitDate,
+            "GIT_COMMITTER_DATE" to commitDate,
+        )
         if (author == null) {
-            git("commit", "-m", message)
+            gitWithEnvironment(environment, "commit", "-m", message)
         } else {
-            git("commit", "--author", author, "-m", message)
+            gitWithEnvironment(environment, "commit", "--author", author, "-m", message)
         }
     }
 
@@ -85,4 +92,15 @@ class NativeLevelSetup internal constructor(
     fun tag(name: String) {
         git("tag", "-f", name)
     }
+
+    private fun gitWithEnvironment(environment: Map<String, String>, vararg arguments: String): Int {
+        return runGit(sandbox, arguments.toList(), environment)
+    }
+
+    private fun nextDeterministicCommitDate(): String {
+        commitSequence += 1
+        val minute = (commitSequence / 60).toString().padStart(2, '0')
+        val second = (commitSequence % 60).toString().padStart(2, '0')
+        return "2000-01-01T00:$minute:$second+0000"
+    }
 }

app/src/main/java/solutions/tretter/githugandroid/levels/BisectLevel.kt

@@ -10,16 +10,19 @@ package solutions.tretter.githugandroid
 internal fun bisectLevel(): Level = level(
     id = "bisect",
     title = "Bisect",
-    description = "A balance check started failing somewhere in the history. Run `./test-balance.sh` to test the current commit. Use `git bisect` to identify the first bad commit.",
+    description = "A balance check started failing somewhere in the history. The current HEAD is bad: `./test-balance.sh` prints `balance broken`. Use `git bisect` to locate the break, then enter the abbreviated hash of the last good commit.",
     hints = listOf(
-        "Start with a known bad commit and a known good commit.",
+        "Mark the current HEAD as bad, because the test fails there.",
         "`known-good` marks a commit where the balance check passes.",
-        "You can automate the search with `git bisect run ./test-balance.sh`.",
+        "`git bisect run ./test-balance.sh` identifies the first bad commit; the last good commit is its parent in this linear history.",
     ),
     commandSuggestions = listOf(
         "./test-balance.sh",
-        "git bisect start HEAD known-good",
+        "git bisect start",
+        "git bisect bad HEAD",
+        "git bisect good known-good",
         "git bisect run ./test-balance.sh",
+        "git rev-parse --short HEAD^",
     ),
     setup = {
         RepoState(
@@ -68,22 +71,26 @@ internal fun bisectLevel(): Level = level(
         addCommit("Update help text", "README")
         append("notes.txt", "Forecast still depends on the balance check\n")
         addCommit("Add forecast note", "notes.txt")
-        append("README", "Use git bisect to find the first broken commit.\n")
+        append("README", "Use git bisect to find the last good commit before the report broke.\n")
         addCommit("Polish report labels", "README")
         true
     },
     validator = { repo, command ->
-        val badCommit = repo.commits.firstOrNull { it.message == "Break closing balance calculation" }
+        val lastGoodCommit = repo.commits.firstOrNull { it.message == "Add audit note" }
         val normalized = command.trim()
-        val answerMatches = badCommit != null &&
-            normalized.isNotBlank() &&
+        lastGoodCommit != null &&
+            normalized.length >= 4 &&
             !normalized.startsWith("git ") &&
-            (normalized.startsWith(badCommit.id, ignoreCase = true) || badCommit.id.startsWith(normalized, ignoreCase = true))
-        val bisectFoundBadCommit = normalized.startsWith("git bisect run", ignoreCase = true) &&
-            "bisect-found" in repo.maintenanceActions
-        answerMatches || bisectFoundBadCommit
+            (normalized.startsWith(lastGoodCommit.id, ignoreCase = true) || lastGoodCommit.id.startsWith(normalized, ignoreCase = true))
     },
     testCases = listOf(
-        levelTestCase("automated bisect", "git bisect start HEAD known-good", "git bisect run ./test-balance.sh"),
+        levelTestCase(
+            "answer last good commit",
+            "git bisect start",
+            "git bisect bad HEAD",
+            "git bisect good known-good",
+            "git bisect run ./test-balance.sh",
+            "c8c7c00",
+        ),
     ),
 )

app/src/test/java/solutions/tretter/githugandroid/LevelSolutionsTest.kt

@@ -139,6 +139,19 @@ class LevelSolutionsTest {
             "A normal commit using the current system date must not solve the commit_in_future level.",
             futureCommitExercise.validator(currentDateCommitRepo, "git commit -m \"Current date commit\""),
         )
+
+        val bisectExercise = bisectLevel()
+        val bisectRuntime = GitRepositoryRuntime(runtimeRoot, gitBinary)
+        var bisectRepo = bisectRuntime.prepareLevel(bisectExercise)
+        listOf("git bisect start", "git bisect bad HEAD", "git bisect good known-good").forEach { command ->
+            val (nextRepo, _) = bisectRuntime.execute(bisectExercise, bisectRepo, command)
+            bisectRepo = nextRepo
+        }
+        val (bisectRunRepo, _) = bisectRuntime.execute(bisectExercise, bisectRepo, "git bisect run ./test-balance.sh")
+        assertFalse(
+            "Running bisect should not solve the bisect level until the learner enters the last good commit hash.",
+            bisectExercise.validator(bisectRunRepo, "git bisect run ./test-balance.sh"),
+        )
     }
 
     private companion object {