Add skip-lts-prepass input to optimize .NET SDK installation process (#791)

- Introduced `skip-lts-prepass` input to allow users to skip the LTS runtime pre-pass during installation.
- Updated documentation to explain the new input and its usage.
- Enhanced tests to verify the behavior of the `skip-lts-prepass` functionality.

Co-authored-by: chiranjib-swain <chiranjib-swain@github.com>

.github/workflows/e2e-tests.yml

@@ -769,3 +769,24 @@ jobs:
             throw "Expected 9.0.100 to be reused, got '${{ steps.reuse.outputs.dotnet-version }}'."
           }
           __tests__/verify-dotnet.ps1 -Patterns "^9\.0\.100$"
+
+  test-skip-lts-prepass:
+    runs-on: ${{ matrix.operating-system }}
+    strategy:
+      fail-fast: false
+      matrix:
+        operating-system: [ubuntu-latest, windows-latest]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Clear toolcache
+        shell: pwsh
+        run: __tests__/clear-toolcache.ps1 ${{ runner.os }}
+      - name: Setup dotnet 9.0.308 with skip-lts-prepass
+        uses: ./
+        with:
+          dotnet-version: 9.0.308
+          skip-lts-prepass: true
+      - name: Verify dotnet
+        shell: pwsh
+        run: __tests__/verify-dotnet.ps1 -Patterns "^9\.0\.308$"

README.md

@@ -86,6 +86,21 @@ steps:
     dotnet-channel: LTS
 ```
 
+## Using the `skip-lts-prepass` input
+
+By default, `setup-dotnet` installs a minimal LTS runtime before installing the requested `dotnet-version`, to guarantee a stable `dotnet` executable is available. If your workflow doesn't need this safeguard (for example, the runner image already has a `dotnet` executable, or you're on a clean self-hosted/container environment and want to avoid the extra download), set `skip-lts-prepass: true` to install only the requested version.
+
+```yaml
+steps:
+- uses: actions/checkout@v7
+- uses: actions/setup-dotnet@v6
+  with:
+    dotnet-version: '9.0.x'
+    skip-lts-prepass: true
+```
+
+> **Note**: Setting skip-lts-prepass: true skips the LTS runtime pre-pass, so the action won't proactively install the latest LTS runtime. The existing dotnet executable and host components will be used if present; on a clean machine, they will come from the requested SDK installation. Consequently, dotnet --info may report a different Host: Version than when the pre-pass runs.
+
 ## Using the `architecture` input
 Using the architecture input, it is possible to specify the required .NET SDK architecture. Possible values:  `x64`, `x86`, `arm64`, `amd64`, `arm`, `s390x`, `ppc64le`, `riscv64`. If the input is not specified, the architecture defaults to the host OS architecture (not all of the architectures are available on all platforms).
 

__tests__/installer.test.ts

@@ -1218,6 +1218,135 @@ describe('installer tests', () => {
           }
         );
       });
+
+      describe('skip-lts-prepass tests', () => {
+        it('should run the LTS pre-pass by default (skip-lts-prepass not set)', async () => {
+          const inputVersion = '9.0.100';
+          const inputQuality = '';
+          const stdout = `Fictitious dotnet version ${inputVersion} is installed`;
+
+          getExecOutputSpy.mockImplementation(() => {
+            return Promise.resolve({exitCode: 0, stdout, stderr: ''});
+          });
+          maxSatisfyingSpy.mockImplementation(() => inputVersion);
+
+          const dotnetInstaller = new installer.DotnetCoreInstaller(
+            inputVersion,
+            inputQuality
+          );
+          await dotnetInstaller.installDotnet();
+
+          expect(getExecOutputSpy).toHaveBeenCalledTimes(2);
+          const ltsCallArguments = (
+            getExecOutputSpy.mock.calls[0][1] as string[]
+          ).join(' ');
+          expect(ltsCallArguments).toContain(
+            IS_WINDOWS ? '-Channel LTS' : '--channel LTS'
+          );
+        });
+
+        it('should skip the LTS pre-pass and install only the requested version when skip-lts-prepass is true', async () => {
+          const inputVersion = '9.0.100';
+          const inputQuality = '';
+          const stdout = `Fictitious dotnet version ${inputVersion} is installed`;
+
+          getExecOutputSpy.mockImplementation(() => {
+            return Promise.resolve({exitCode: 0, stdout, stderr: ''});
+          });
+          maxSatisfyingSpy.mockImplementation(() => inputVersion);
+
+          const dotnetInstaller = new installer.DotnetCoreInstaller(
+            inputVersion,
+            inputQuality,
+            undefined,
+            undefined,
+            true,
+            undefined,
+            undefined,
+            true
+          );
+          const installedVersion = await dotnetInstaller.installDotnet();
+
+          expect(getExecOutputSpy).toHaveBeenCalledTimes(1);
+          const scriptArguments = (
+            getExecOutputSpy.mock.calls[0][1] as string[]
+          ).join(' ');
+          expect(scriptArguments).not.toContain('LTS');
+          expect(scriptArguments).toContain(
+            IS_WINDOWS
+              ? `-Version ${inputVersion}`
+              : `--version ${inputVersion}`
+          );
+          expect(installedVersion).toBe(inputVersion);
+        });
+
+        it('should skip the LTS pre-pass for a cross-architecture install', async () => {
+          const inputVersion = '9.0.100';
+          const inputQuality = '';
+          const inputArchitecture =
+            installer.normalizeArch(os.arch()) === 'x64' ? 'arm64' : 'x64';
+          const stdout = `Fictitious dotnet version ${inputVersion} is installed`;
+
+          getExecOutputSpy.mockImplementation(() => {
+            return Promise.resolve({exitCode: 0, stdout, stderr: ''});
+          });
+          maxSatisfyingSpy.mockImplementation(() => inputVersion);
+
+          const dotnetInstaller = new installer.DotnetCoreInstaller(
+            inputVersion,
+            inputQuality,
+            inputArchitecture,
+            undefined,
+            true,
+            undefined,
+            undefined,
+            true
+          );
+          await dotnetInstaller.installDotnet();
+
+          expect(getExecOutputSpy).toHaveBeenCalledTimes(1);
+          const scriptArguments = (
+            getExecOutputSpy.mock.calls[0][1] as string[]
+          ).join(' ');
+          expect(scriptArguments).not.toContain('LTS');
+          expect(scriptArguments).toContain(
+            IS_WINDOWS ? '-Architecture' : '--architecture'
+          );
+        });
+
+        it('should skip the LTS pre-pass for each requested version', async () => {
+          const inputQuality = '';
+
+          getExecOutputSpy.mockImplementation(() => {
+            return Promise.resolve({
+              exitCode: 0,
+              stdout: `Fictitious dotnet version installed`,
+              stderr: ''
+            });
+          });
+          maxSatisfyingSpy.mockImplementation(() => '9.0.100');
+
+          for (const version of ['8.0.100', '9.0.100']) {
+            const dotnetInstaller = new installer.DotnetCoreInstaller(
+              version,
+              inputQuality,
+              undefined,
+              undefined,
+              true,
+              undefined,
+              undefined,
+              true
+            );
+            await dotnetInstaller.installDotnet();
+          }
+
+          // 2 versions x 1 call each (no LTS pre-pass call for either)
+          expect(getExecOutputSpy).toHaveBeenCalledTimes(2);
+          for (const call of getExecOutputSpy.mock.calls) {
+            expect((call[1] as string[]).join(' ')).not.toContain('LTS');
+          }
+        });
+      });
     });
 
     describe('addToPath() tests', () => {

__tests__/setup-dotnet.test.ts

@@ -315,6 +315,44 @@ describe('setup-dotnet tests', () => {
       expect(capturedCheckLatest).toBe(false);
     });
 
+    it("should read the 'skip-lts-prepass' input and pass it to DotnetCoreInstaller", async () => {
+      inputs['dotnet-version'] = ['10.0.101'];
+      inputs['dotnet-quality'] = '';
+      inputs['architecture'] = '';
+      inputs['skip-lts-prepass'] = 'true';
+
+      let capturedSkipLtsPrepass: boolean | undefined;
+      installDotnetSpy.mockImplementation(function (this: any) {
+        capturedSkipLtsPrepass = this.skipLtsPrepass;
+        return Promise.resolve('');
+      });
+
+      await setup.run();
+
+      expect(getBooleanInputSpy).toHaveBeenCalledWith('skip-lts-prepass');
+      expect(installDotnetSpy).toHaveBeenCalledTimes(1);
+      expect(capturedSkipLtsPrepass).toBe(true);
+    });
+
+    it("should default 'skip-lts-prepass' to false when the input isn't set", async () => {
+      inputs['dotnet-version'] = ['10.0.101'];
+      inputs['dotnet-quality'] = '';
+      inputs['architecture'] = '';
+      inputs['skip-lts-prepass'] = '';
+
+      let capturedSkipLtsPrepass: boolean | undefined;
+      installDotnetSpy.mockImplementation(function (this: any) {
+        capturedSkipLtsPrepass = this.skipLtsPrepass;
+        return Promise.resolve('');
+      });
+
+      await setup.run();
+
+      expect(getBooleanInputSpy).toHaveBeenCalledWith('skip-lts-prepass');
+      expect(installDotnetSpy).toHaveBeenCalledTimes(1);
+      expect(capturedSkipLtsPrepass).toBe(false);
+    });
+
     describe("'check-latest' resolution", () => {
       const captureCheckLatest = async () => {
         inputs['dotnet-version'] = ['10.0.101'];

action.yml

@@ -14,6 +14,10 @@ inputs:
   dotnet-channel:
     description: 'Optional channel for the installation. The possible values are: STS, LTS, A.B (e.g. 8.0), A.B.Cxx (e.g. 8.0.1xx, available since 5.0). To be used with "dotnet-version: latest".'
     required: false
+  skip-lts-prepass:
+    description: 'Optional. When true, skips the LTS runtime pre-pass and installs only the requested dotnet-version. Default: false.'
+    required: false
+    default: false
   global-json-file:
     description: 'Optional global.json location, if your global.json isn''t located in the root of the repo.'
     required: false

dist/setup/index.js

@@ -45382,11 +45382,12 @@ class DotnetCoreInstaller {
     checkLatest;
     minimumVersion;
     rollForward;
+    skipLtsPrepass;
     static FeatureBandSyntax = /^(\d+)\.(\d+)\.(\d)xx$/;
     static {
         DotnetInstallDir.setEnvironmentVariable();
     }
-    constructor(version, quality, architecture, dotnetChannel, checkLatest = true, minimumVersion, rollForward) {
+    constructor(version, quality, architecture, dotnetChannel, checkLatest = true, minimumVersion, rollForward, skipLtsPrepass = false) {
         this.version = version;
         this.quality = quality;
         this.architecture = architecture;
@@ -45394,6 +45395,7 @@ class DotnetCoreInstaller {
         this.checkLatest = checkLatest;
         this.minimumVersion = minimumVersion;
         this.rollForward = rollForward;
+        this.skipLtsPrepass = skipLtsPrepass;
         this.version = version.trim();
     }
     getInstalledSdkVersions() {
@@ -45594,8 +45596,10 @@ class DotnetCoreInstaller {
             : [];
         /**
          * Install dotnet runtime first in order to get
-         * the latest stable version of dotnet CLI
+         * the latest stable version of dotnet CLI.
+         * Opt-out via skip-lts-prepass when this safeguard isn't needed.
          */
+        if (!this.skipLtsPrepass) {
             const runtimeInstallOutput = await new DotnetInstallScript()
                 .useArchitecture(this.architecture)
                 // If dotnet CLI is already installed - avoid overwriting it
@@ -45613,6 +45617,10 @@ class DotnetCoreInstaller {
                  */
                 warning(`Failed to install dotnet runtime + cli, exit code: ${runtimeInstallOutput.exitCode}. ${runtimeInstallOutput.stderr}`);
             }
+        }
+        else {
+            info('Skipping LTS runtime pre-pass (skip-lts-prepass: true).');
+        }
         /**
          * Install dotnet over the latest version of
          * dotnet CLI
@@ -106872,11 +106880,12 @@ async function run() {
             if (quality && !qualityOptions.includes(quality)) {
                 throw new Error(`Value '${quality}' is not supported for the 'dotnet-quality' option. Supported values are: daily, preview, ga.`);
             }
+            const skipLtsPrepass = getBooleanInput('skip-lts-prepass');
             let dotnetInstaller;
             const uniqueVersions = new Set(versions.map(v => (v.toLowerCase() === 'latest' ? 'latest' : v)));
             for (const version of uniqueVersions) {
                 const constraint = globalJsonConstraints.get(version);
-                dotnetInstaller = new DotnetCoreInstaller(version, quality, architecture, version.toLowerCase() === 'latest' ? dotnetChannel : undefined, checkLatest, constraint?.minimumVersion, constraint?.rollForward);
+                dotnetInstaller = new DotnetCoreInstaller(version, quality, architecture, version.toLowerCase() === 'latest' ? dotnetChannel : undefined, checkLatest, constraint?.minimumVersion, constraint?.rollForward, skipLtsPrepass);
                 const installedVersion = await dotnetInstaller.installDotnet();
                 installedDotnetVersions.push(installedVersion);
             }

src/installer.ts

@@ -421,7 +421,8 @@ export class DotnetCoreInstaller {
     private dotnetChannel?: string,
     private checkLatest: boolean = true,
     private minimumVersion?: string,
-    private rollForward?: string
+    private rollForward?: string,
+    private skipLtsPrepass: boolean = false
   ) {
     this.version = version.trim();
   }
@@ -720,8 +721,10 @@ export class DotnetCoreInstaller {
       : [];
     /**
      * Install dotnet runtime first in order to get
-     * the latest stable version of dotnet CLI
+     * the latest stable version of dotnet CLI.
+     * Opt-out via skip-lts-prepass when this safeguard isn't needed.
      */
+    if (!this.skipLtsPrepass) {
       const runtimeInstallOutput = await new DotnetInstallScript()
         .useArchitecture(this.architecture)
         // If dotnet CLI is already installed - avoid overwriting it
@@ -744,6 +747,9 @@ export class DotnetCoreInstaller {
           `Failed to install dotnet runtime + cli, exit code: ${runtimeInstallOutput.exitCode}. ${runtimeInstallOutput.stderr}`
         );
       }
+    } else {
+      core.info('Skipping LTS runtime pre-pass (skip-lts-prepass: true).');
+    }
 
     /**
      * Install dotnet over the latest version of

src/setup-dotnet.ts

@@ -130,6 +130,8 @@ export async function run() {
         );
       }
 
+      const skipLtsPrepass = core.getBooleanInput('skip-lts-prepass');
+
       let dotnetInstaller: DotnetCoreInstaller;
       const uniqueVersions = new Set<string>(
         versions.map(v => (v.toLowerCase() === 'latest' ? 'latest' : v))
@@ -143,7 +145,8 @@ export async function run() {
           version.toLowerCase() === 'latest' ? dotnetChannel : undefined,
           checkLatest,
           constraint?.minimumVersion,
-          constraint?.rollForward
+          constraint?.rollForward,
+          skipLtsPrepass
         );
         const installedVersion = await dotnetInstaller.installDotnet();
         installedDotnetVersions.push(installedVersion);