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() {
@@ -45594,24 +45596,30 @@ 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.
          */
-        const runtimeInstallOutput = await new DotnetInstallScript()
-            .useArchitecture(this.architecture)
-            // If dotnet CLI is already installed - avoid overwriting it
-            .useArguments(utils_IS_WINDOWS ? '-SkipNonVersionedFiles' : '--skip-non-versioned-files')
-            // Install only runtime + CLI
-            .useArguments(utils_IS_WINDOWS ? '-Runtime' : '--runtime', 'dotnet')
-            // Use latest stable version
-            .useArguments(utils_IS_WINDOWS ? '-Channel' : '--channel', 'LTS')
-            .useArguments(...architectureArguments)
-            .execute();
-        if (runtimeInstallOutput.exitCode) {
-            /**
-             * dotnetInstallScript will install CLI and runtime even if previous script haven't succeded,
-             * so at this point it's too early to throw an error
-             */
-            warning(`Failed to install dotnet runtime + cli, exit code: ${runtimeInstallOutput.exitCode}. ${runtimeInstallOutput.stderr}`);
+        if (!this.skipLtsPrepass) {
+            const runtimeInstallOutput = await new DotnetInstallScript()
+                .useArchitecture(this.architecture)
+                // If dotnet CLI is already installed - avoid overwriting it
+                .useArguments(utils_IS_WINDOWS ? '-SkipNonVersionedFiles' : '--skip-non-versioned-files')
+                // Install only runtime + CLI
+                .useArguments(utils_IS_WINDOWS ? '-Runtime' : '--runtime', 'dotnet')
+                // Use latest stable version
+                .useArguments(utils_IS_WINDOWS ? '-Channel' : '--channel', 'LTS')
+                .useArguments(...architectureArguments)
+                .execute();
+            if (runtimeInstallOutput.exitCode) {
+                /**
+                 * dotnetInstallScript will install CLI and runtime even if previous script haven't succeded,
+                 * so at this point it's too early to throw an error
+                 */
+                warning(`Failed to install dotnet runtime + cli, exit code: ${runtimeInstallOutput.exitCode}. ${runtimeInstallOutput.stderr}`);
+            }
+        }
+        else {
+            info('Skipping LTS runtime pre-pass (skip-lts-prepass: true).');
         }
         /**
          * Install dotnet over the latest version of
@@ -106872,11 +106880,12 @@ async function run() {
             if (quality && !qualityOptions.includes(quality)) {
                 throw new Error(`Value '${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);
             }

package-lock.json

@@ -36,7 +36,7 @@
         "husky": "^9.1.7",
         "jest": "^30.4.2",
         "jest-circus": "^30.4.2",
-        "jest-each": "^30.5.2",
+        "jest-each": "^30.0.0",
         "prettier": "^3.8.4",
         "ts-jest": "^29.4.11",
         "typescript": "^6.0.3",
@@ -1425,22 +1425,6 @@
         "node": "^18.14.0 || ^20.0.0 || ^22.0.0 || >=24.0.0"
       }
     },
-    "node_modules/@jest/react-is-18": {
-      "name": "react-is",
-      "version": "18.3.1",
-      "resolved": "https://registry.npmjs.org/react-is/-/react-is-18.3.1.tgz",
-      "integrity": "sha512-/LLMVyas0ljjAtoYiPqYiL8VWXzUUdThrmU5+n20DZv+a+ClRoevUzw5JxU+Ieh5/c87ytoTBV9G1FiKfNJdmg==",
-      "dev": true,
-      "license": "MIT"
-    },
-    "node_modules/@jest/react-is-19": {
-      "name": "react-is",
-      "version": "19.3.0",
-      "resolved": "https://registry.npmjs.org/react-is/-/react-is-19.3.0.tgz",
-      "integrity": "sha512-UpMYezM4v5/18F28aC66AEsjXIgE02kyEMH6yLdgLXu/UTfa1Ntwck/nNLrbqJsEXW7gPb0coNO9FQse9WTovA==",
-      "dev": true,
-      "license": "MIT"
-    },
     "node_modules/@jest/reporters": {
       "version": "30.4.1",
       "resolved": "https://registry.npmjs.org/@jest/reporters/-/reporters-30.4.1.tgz",
@@ -4509,23 +4493,6 @@
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       }
     },
-    "node_modules/jest-circus/node_modules/jest-each": {
-      "version": "30.4.1",
-      "resolved": "https://registry.npmjs.org/jest-each/-/jest-each-30.4.1.tgz",
-      "integrity": "sha512-/8MJbH6fuj48TstjrMf+u/pd06Qezz5xOXvZA6442heNOWr8bdeoGZX2d9fCn028CoMgYmroH9//zky5GfyYmA==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "@jest/get-type": "30.1.0",
-        "@jest/types": "30.4.1",
-        "chalk": "^4.1.2",
-        "jest-util": "30.4.1",
-        "pretty-format": "30.4.1"
-      },
-      "engines": {
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-      }
-    },
     "node_modules/jest-cli": {
       "version": "30.4.2",
       "resolved": "https://registry.npmjs.org/jest-cli/-/jest-cli-30.4.2.tgz",
@@ -4640,144 +4607,17 @@
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     },
     "node_modules/jest-each": {
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       "dev": true,
       "license": "MIT",
       "dependencies": {
-        "@jest/get-type": "30.5.0",
-        "@jest/types": "30.5.1",
+        "@jest/get-type": "30.1.0",
+        "@jest/types": "30.4.1",
         "chalk": "^4.1.2",
-        "jest-regex-util": "30.5.0",
-        "jest-util": "30.5.1",
-        "pretty-format": "30.5.1"
-      },
-      "engines": {
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-      }
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-      "version": "4.0.7",
-      "resolved": "https://registry.npmjs.org/picomatch/-/picomatch-4.0.7.tgz",
-      "integrity": "sha512-qcJu88Q2IWqJsDD529JKMdwGm/dvInW4HvQnRwiH9JtihJvzGOscDtHE3x1pBKeUOTysQ8kVmLnJ2kJu7yhcGA==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=12"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/jonschlinkert"
-      }
-    },
-    "node_modules/jest-each/node_modules/pretty-format": {
-      "version": "30.5.1",
-      "resolved": "https://registry.npmjs.org/pretty-format/-/pretty-format-30.5.1.tgz",
-      "integrity": "sha512-byhRAPguVKMQIj4kjJwJ5lAskVhfuiSdiYl/aLTWpgkGEmic2jYhJh1yE9ih8Ox44Xg9ccCT11/S6QrzSJuNrg==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "@jest/react-is-18": "npm:react-is@^18.3.1",
-        "@jest/react-is-19": "npm:react-is@^19.2.5",
-        "@jest/schemas": "30.5.0",
-        "ansi-styles": "^5.2.0"
+        "jest-util": "30.4.1",
+        "pretty-format": "30.4.1"
       },
       "engines": {
         "node": "^18.14.0 || ^20.0.0 || ^22.0.0 || >=24.0.0"

package.json

@@ -57,7 +57,7 @@
     "husky": "^9.1.7",
     "jest": "^30.4.2",
     "jest-circus": "^30.4.2",
-    "jest-each": "^30.5.2",
+    "jest-each": "^30.0.0",
     "prettier": "^3.8.4",
     "ts-jest": "^29.4.11",
     "typescript": "^6.0.3",

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();
   }
@@ -720,29 +721,34 @@ 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.
      */
-    const runtimeInstallOutput = await new DotnetInstallScript()
-      .useArchitecture(this.architecture)
-      // If dotnet CLI is already installed - avoid overwriting it
-      .useArguments(
-        IS_WINDOWS ? '-SkipNonVersionedFiles' : '--skip-non-versioned-files'
-      )
-      // Install only runtime + CLI
-      .useArguments(IS_WINDOWS ? '-Runtime' : '--runtime', 'dotnet')
-      // Use latest stable version
-      .useArguments(IS_WINDOWS ? '-Channel' : '--channel', 'LTS')
-      .useArguments(...architectureArguments)
-      .execute();
+    if (!this.skipLtsPrepass) {
+      const runtimeInstallOutput = await new DotnetInstallScript()
+        .useArchitecture(this.architecture)
+        // If dotnet CLI is already installed - avoid overwriting it
+        .useArguments(
+          IS_WINDOWS ? '-SkipNonVersionedFiles' : '--skip-non-versioned-files'
+        )
+        // Install only runtime + CLI
+        .useArguments(IS_WINDOWS ? '-Runtime' : '--runtime', 'dotnet')
+        // Use latest stable version
+        .useArguments(IS_WINDOWS ? '-Channel' : '--channel', 'LTS')
+        .useArguments(...architectureArguments)
+        .execute();
 
-    if (runtimeInstallOutput.exitCode) {
-      /**
-       * dotnetInstallScript will install CLI and runtime even if previous script haven't succeded,
-       * so at this point it's too early to throw an error
-       */
-      core.warning(
-        `Failed to install dotnet runtime + cli, exit code: ${runtimeInstallOutput.exitCode}. ${runtimeInstallOutput.stderr}`
-      );
+      if (runtimeInstallOutput.exitCode) {
+        /**
+         * dotnetInstallScript will install CLI and runtime even if previous script haven't succeded,
+         * so at this point it's too early to throw an error
+         */
+        core.warning(
+          `Failed to install dotnet runtime + cli, exit code: ${runtimeInstallOutput.exitCode}. ${runtimeInstallOutput.stderr}`
+        );
+      }
+    } else {
+      core.info('Skipping LTS runtime pre-pass (skip-lts-prepass: true).');
     }
 
     /**

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);