feat: support platform-specific SHA256 verification

Adds support for platform-specific BAZELISK_VERIFY_SHA256 variables,
enabling SHA256 verification in multiplatform projects.

Bazelisk now checks for configuration in the following order:
1. BAZELISK_VERIFY_SHA256_NOJDK_<OS>_<ARCH> (when BAZELISK_NOJDK is enabled)
2. BAZELISK_VERIFY_SHA256_<OS>_<ARCH>
3. BAZELISK_VERIFY_SHA256 (existing behavior, fallback)

Implementation notes:
- Refactored downloadBazelIfNecessary to compute platform info once upfront
- Added FormatBazelFilename helper to avoid redundant OS/arch computation
- Hash values normalized to lowercase for case-insensitive comparison
- Full backward compatibility maintained

Fixes #522

Author: albertocavalcante

README.md

@@ -77,7 +77,13 @@ Note: `last_downstream_green` support has been removed, please use `last_green`
 
 ## Where does Bazelisk get Bazel from?
 
-By default Bazelisk retrieves Bazel releases, release candidates and binaries built at green commits from Google Cloud Storage. The downloaded artifacts are validated against the SHA256 value recorded in `BAZELISK_VERIFY_SHA256` if this variable is set in the configuration file.
+By default Bazelisk retrieves Bazel releases, release candidates and binaries built at green commits from Google Cloud Storage. The downloaded artifacts can be validated against an expected SHA256 hash.
+
+Since each platform has a different binary with a different hash, Bazelisk supports platform-specific hash variables:
+
+- `BAZELISK_VERIFY_SHA256_<OS>_<ARCH>` - hash for a specific platform (e.g., `BAZELISK_VERIFY_SHA256_LINUX_X86_64`)
+- `BAZELISK_VERIFY_SHA256_NOJDK_<OS>_<ARCH>` - hash for nojdk builds (when `BAZELISK_NOJDK` is enabled)
+- `BAZELISK_VERIFY_SHA256` - fallback used when no platform-specific hash is set
 
 As mentioned in the previous section, the `<FORK>/<VERSION>` version format allows you to use your own Bazel fork hosted on GitHub:
 
@@ -270,6 +276,8 @@ The following variables can be set:
 - `BAZELISK_SKIP_WRAPPER`
 - `BAZELISK_USER_AGENT`
 - `BAZELISK_VERIFY_SHA256`
+- `BAZELISK_VERIFY_SHA256_<OS>_<ARCH>` (e.g., `BAZELISK_VERIFY_SHA256_DARWIN_ARM64`)
+- `BAZELISK_VERIFY_SHA256_NOJDK_<OS>_<ARCH>` (e.g., `BAZELISK_VERIFY_SHA256_NOJDK_LINUX_X86_64`)
 - `USE_BAZEL_VERSION`
 
 Configuration variables are evaluated with precedence order. The preferred values are derived in order from highest to lowest precedence as follows:
@@ -278,7 +286,7 @@ Configuration variables are evaluated with precedence order. The preferred value
 * Variables defined in the workspace root `.bazeliskrc`
 * Variables defined in the user home `.bazeliskrc`
 
-Additionally, the Bazelisk home directory is also evaluated in precedence order. The preferred value is OS-specific e.g. `BAZELISK_HOME_LINUX`, then we fall back to `BAZELISK_HOME`.
+Some variables support platform-specific variants. For example, `BAZELISK_HOME_LINUX` takes precedence over `BAZELISK_HOME`, and `BAZELISK_VERIFY_SHA256_DARWIN_ARM64` takes precedence over `BAZELISK_VERIFY_SHA256`.
 
 ## Requirements
 

bazelisk_test.sh

@@ -448,6 +448,78 @@ function test_bazel_verify_sha256() {
       (echo "FAIL: Expected to find 'Build label' in the output of 'bazelisk version'"; exit 1)
 }
 
+function test_bazel_verify_sha256_platform_specific() {
+  setup
+
+  echo "9.0.0" > .bazelversion
+
+  local os="$(uname -s | tr A-Z a-z)"
+  local arch="$(uname -m)"
+
+  # Map to bazelisk naming convention
+  case "${arch}" in
+    x86_64|amd64)
+      arch="X86_64"
+      ;;
+    arm64|aarch64)
+      arch="ARM64"
+      ;;
+  esac
+
+  # SHA256 hashes for Bazel 9.0.0 binaries.
+  # Mixed case is intentional to test hash normalization.
+  case "${os}" in
+    darwin)
+      os_upper="DARWIN"
+      if [[ "${arch}" == "ARM64" ]]; then
+        expected_sha256="2c3cce548a4b6a97A2A5267712187b784b52714c4a2b0613e7386b15669d783c"
+      else
+        expected_sha256="aa7e5fc364eaaba7f4f271dbf8c14172a5433f663cca6b130325df4b6569b3f0"
+      fi
+      ;;
+    linux)
+      os_upper="LINUX"
+      if [[ "${arch}" == "ARM64" ]]; then
+        expected_sha256="cab23c59d3d39c5E5382F12cd116b47445afdff9813516c18ae3ee8836b3037f"
+      else
+        expected_sha256="C44A93f25398c68f904fa1d19b61d321de6c0d2f09dca375d7bc0dc9b9428403"
+      fi
+      ;;
+    msys*|mingw*|cygwin*)
+      os_upper="WINDOWS"
+      if [[ "${arch}" == "ARM64" ]]; then
+        expected_sha256="ab3db0b1f129436180927Baa0f1f38e6d86a88fc9ee802572a76c9519a06f550"
+      else
+        expected_sha256="463faee497df2913854D80776784137cb47f42960b4ef4e4f85068c8da4849a8"
+      fi
+      ;;
+    *)
+      echo "FAIL: Unknown OS ${os} in test"
+      exit 1
+      ;;
+  esac
+
+  local platform_var="BAZELISK_VERIFY_SHA256_${os_upper}_${arch}"
+
+  # Test 1: Platform-specific variable should work
+  env BAZELISK_HOME="$BAZELISK_HOME" "${platform_var}=${expected_sha256}" \
+      bazelisk version 2>&1 | tee log
+
+  grep "Build label:" log || \
+      (echo "FAIL: Expected to find 'Build label' with platform-specific hash"; exit 1)
+
+  # Test 2: Platform-specific should take precedence over generic
+  rm -rf "$BAZELISK_HOME/downloads"
+
+  env BAZELISK_HOME="$BAZELISK_HOME" \
+      BAZELISK_VERIFY_SHA256="wrong-generic-hash" \
+      "${platform_var}=${expected_sha256}" \
+      bazelisk version 2>&1 | tee log
+
+  grep "Build label:" log || \
+      (echo "FAIL: Platform-specific should take precedence over generic"; exit 1)
+}
+
 function test_bazel_download_path_py() {
   setup
 
@@ -570,6 +642,10 @@ if [[ $BAZELISK_VERSION == "GO" ]]; then
   test_bazel_verify_sha256
   echo
 
+  echo '# test_bazel_verify_sha256_platform_specific'
+  test_bazel_verify_sha256_platform_specific
+  echo
+
   echo "# test_bazel_prepend_binary_directory_to_path_go"
   test_bazel_prepend_binary_directory_to_path_go
   echo

core/core.go

@@ -441,11 +441,17 @@ func downloadBazel(bazelVersionString string, bazeliskHome string, repos *Reposi
 //	downloads/metadata/[fork-or-url]/bazel-[version-os-etc] is a text file containing a hex sha256 of the contents of the downloaded bazel file.
 //	downloads/sha256/[sha256]/bin/bazel[extension] contains the bazel with a particular sha256.
 func downloadBazelIfNecessary(version string, bazeliskHome string, bazelForkOrURLDirName string, repos *Repositories, config config.Config, downloader DownloadFunc) (string, error) {
-	pathSegment, err := platforms.DetermineBazelFilename(version, false, config)
+	osName, err := platforms.DetermineOperatingSystem()
 	if err != nil {
-		return "", fmt.Errorf("could not determine path segment to use for Bazel binary: %v", err)
+		return "", fmt.Errorf("could not determine operating system: %v", err)
 	}
+	arch, err := platforms.DetermineArchitecture(osName, version)
+	if err != nil {
+		return "", fmt.Errorf("could not determine architecture: %v", err)
+	}
+	isNojdk := platforms.IsNojdkEnabled(config)
 
+	pathSegment := platforms.FormatBazelFilename(version, false, osName, arch, isNojdk)
 	destFile := "bazel" + platforms.DetermineExecutableFilenameSuffix()
 
 	mappingPath := filepath.Join(bazeliskHome, "downloads", "metadata", bazelForkOrURLDirName, pathSegment)
@@ -462,7 +468,7 @@ func downloadBazelIfNecessary(version string, bazeliskHome string, bazelForkOrUR
 		return "", fmt.Errorf("failed to download bazel: %w", err)
 	}
 
-	expectedSha256 := strings.ToLower(config.Get("BAZELISK_VERIFY_SHA256"))
+	expectedSha256 := getExpectedSHA256(config, osName, arch, isNojdk)
 	if len(expectedSha256) > 0 {
 		if expectedSha256 != downloadedDigest {
 			return "", fmt.Errorf("%s has sha256=%s but need sha256=%s", pathToBazelInCAS, downloadedDigest, expectedSha256)
@@ -1508,3 +1514,20 @@ func extractCompletionScriptsFromZip(zipData []byte) (map[string]string, error)
 
 	return completionScripts, nil
 }
+
+// getExpectedSHA256 returns the expected SHA256 hash for verification.
+// It checks platform-specific keys first, then falls back to the generic key.
+// Returns empty string if no hash is configured.
+func getExpectedSHA256(cfg config.Config, osName, arch string, nojdk bool) string {
+	suffix := strings.ToUpper(osName) + "_" + strings.ToUpper(arch)
+
+	if nojdk {
+		if hash := cfg.Get("BAZELISK_VERIFY_SHA256_NOJDK_" + suffix); hash != "" {
+			return strings.ToLower(hash)
+		}
+	}
+	if hash := cfg.Get("BAZELISK_VERIFY_SHA256_" + suffix); hash != "" {
+		return strings.ToLower(hash)
+	}
+	return strings.ToLower(cfg.Get("BAZELISK_VERIFY_SHA256"))
+}

core/core_test.go

@@ -888,3 +888,100 @@ func TestRunBazeliskWithStderrRedirection(t *testing.T) {
 		t.Error("stdout content should not appear in stderr")
 	}
 }
+
+func TestGetExpectedSHA256(t *testing.T) {
+	testCases := []struct {
+		name     string
+		config   map[string]string
+		osName   string
+		arch     string
+		nojdk    bool
+		expected string
+	}{
+		{
+			name: "platform-specific takes precedence",
+			config: map[string]string{
+				"BAZELISK_VERIFY_SHA256":              "generic-hash",
+				"BAZELISK_VERIFY_SHA256_LINUX_X86_64": "platform-hash",
+			},
+			osName:   "linux",
+			arch:     "x86_64",
+			nojdk:    false,
+			expected: "platform-hash",
+		},
+		{
+			name: "falls back to generic when platform-specific not set",
+			config: map[string]string{
+				"BAZELISK_VERIFY_SHA256": "generic-hash",
+			},
+			osName:   "darwin",
+			arch:     "arm64",
+			nojdk:    false,
+			expected: "generic-hash",
+		},
+		{
+			name:     "empty when neither set",
+			config:   map[string]string{},
+			osName:   "windows",
+			arch:     "x86_64",
+			nojdk:    false,
+			expected: "",
+		},
+		{
+			name: "hash is normalized to lowercase",
+			config: map[string]string{
+				"BAZELISK_VERIFY_SHA256_LINUX_ARM64": "AbCdEf123456",
+			},
+			osName:   "linux",
+			arch:     "arm64",
+			nojdk:    false,
+			expected: "abcdef123456",
+		},
+		// nojdk test cases
+		{
+			name: "nojdk-specific takes precedence when nojdk enabled",
+			config: map[string]string{
+				"BAZELISK_VERIFY_SHA256":                    "generic-hash",
+				"BAZELISK_VERIFY_SHA256_LINUX_X86_64":       "platform-hash",
+				"BAZELISK_VERIFY_SHA256_NOJDK_LINUX_X86_64": "nojdk-hash",
+			},
+			osName:   "linux",
+			arch:     "x86_64",
+			nojdk:    true,
+			expected: "nojdk-hash",
+		},
+		{
+			name: "nojdk falls back to platform-specific when nojdk key not set",
+			config: map[string]string{
+				"BAZELISK_VERIFY_SHA256":              "generic-hash",
+				"BAZELISK_VERIFY_SHA256_LINUX_X86_64": "platform-hash",
+			},
+			osName:   "linux",
+			arch:     "x86_64",
+			nojdk:    true,
+			expected: "platform-hash",
+		},
+		{
+			name: "nojdk key ignored when nojdk disabled",
+			config: map[string]string{
+				"BAZELISK_VERIFY_SHA256":                    "generic-hash",
+				"BAZELISK_VERIFY_SHA256_LINUX_X86_64":       "platform-hash",
+				"BAZELISK_VERIFY_SHA256_NOJDK_LINUX_X86_64": "nojdk-hash",
+			},
+			osName:   "linux",
+			arch:     "x86_64",
+			nojdk:    false,
+			expected: "platform-hash",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			cfg := config.Static(tc.config)
+			result := getExpectedSHA256(cfg, tc.osName, tc.arch, tc.nojdk)
+			if result != tc.expected {
+				t.Errorf("getExpectedSHA256() = %q, want %q", result, tc.expected)
+			}
+		})
+	}
+}

platforms/platforms.go

@@ -32,6 +32,12 @@ var supportedPlatforms = map[string]*platform{
 	},
 }
 
+// IsNojdkEnabled returns true if BAZELISK_NOJDK is set to a truthy value.
+func IsNojdkEnabled(config config.Config) bool {
+	v := config.Get("BAZELISK_NOJDK")
+	return v != "" && v != "0"
+}
+
 // GetPlatform returns a Bazel CI-compatible platform identifier for the current operating system.
 // TODO(fweikert): raise an error for unsupported platforms
 func GetPlatform() (string, error) {
@@ -87,14 +93,6 @@ func DetermineOperatingSystem() (string, error) {
 
 // DetermineBazelFilename returns the correct file name of a local Bazel binary.
 func DetermineBazelFilename(version string, includeSuffix bool, config config.Config) (string, error) {
-	flavor := "bazel"
-
-	bazeliskNojdk := config.Get("BAZELISK_NOJDK")
-
-	if len(bazeliskNojdk) != 0 && bazeliskNojdk != "0" {
-		flavor = "bazel_nojdk"
-	}
-
 	osName, err := DetermineOperatingSystem()
 	if err != nil {
 		return "", err
@@ -105,12 +103,22 @@ func DetermineBazelFilename(version string, includeSuffix bool, config config.Co
 		return "", err
 	}
 
+	return FormatBazelFilename(version, includeSuffix, osName, machineName, IsNojdkEnabled(config)), nil
+}
+
+// FormatBazelFilename formats a Bazel binary filename from pre-computed platform values.
+func FormatBazelFilename(version string, includeSuffix bool, osName, machineName string, nojdk bool) string {
+	flavor := "bazel"
+	if nojdk {
+		flavor = "bazel_nojdk"
+	}
+
 	var filenameSuffix string
 	if includeSuffix {
 		filenameSuffix = DetermineExecutableFilenameSuffix()
 	}
 
-	return fmt.Sprintf("%s-%s-%s-%s%s", flavor, version, osName, machineName, filenameSuffix), nil
+	return fmt.Sprintf("%s-%s-%s-%s%s", flavor, version, osName, machineName, filenameSuffix)
 }
 
 // DetermineBazelInstallerFilename returns the correct file name of a Bazel installer script.

platforms/platforms_test.go

@@ -2,6 +2,46 @@ package platforms
 
 import "testing"
 
+func TestFormatBazelFilename(t *testing.T) {
+	tests := []struct {
+		name          string
+		version       string
+		includeSuffix bool
+		osName        string
+		machineName   string
+		nojdk         bool
+		want          string
+	}{
+		{
+			name:          "standard bazel binary",
+			version:       "7.1.1",
+			includeSuffix: false,
+			osName:        "linux",
+			machineName:   "x86_64",
+			nojdk:         false,
+			want:          "bazel-7.1.1-linux-x86_64",
+		},
+		{
+			name:          "nojdk binary",
+			version:       "7.1.1",
+			includeSuffix: false,
+			osName:        "linux",
+			machineName:   "x86_64",
+			nojdk:         true,
+			want:          "bazel_nojdk-7.1.1-linux-x86_64",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := FormatBazelFilename(tt.version, tt.includeSuffix, tt.osName, tt.machineName, tt.nojdk)
+			if got != tt.want {
+				t.Errorf("FormatBazelFilename() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestDarwinFallback(t *testing.T) {
 	type args struct {
 		machineName string