fix(use): do not throw on invalid `packageManager` (#663)

sources/Engine.ts

@@ -293,19 +293,20 @@ export class Engine {
         }
 
         case `Found`: {
-          if (result.spec.name !== locator.name) {
+          const spec = result.getSpec();
+          if (spec.name !== locator.name) {
             if (transparent) {
               if (typeof locator.reference === `function`)
                 fallbackDescriptor.range = await locator.reference();
 
-              debugUtils.log(`Falling back to ${fallbackDescriptor.name}@${fallbackDescriptor.range} in a ${result.spec.name}@${result.spec.range} project`);
+              debugUtils.log(`Falling back to ${fallbackDescriptor.name}@${fallbackDescriptor.range} in a ${spec.name}@${spec.range} project`);
               return fallbackDescriptor;
             } else {
-              throw new UsageError(`This project is configured to use ${result.spec.name} because ${result.target} has a "packageManager" field`);
+              throw new UsageError(`This project is configured to use ${spec.name} because ${result.target} has a "packageManager" field`);
             }
           } else {
-            debugUtils.log(`Using ${result.spec.name}@${result.spec.range} as defined in project manifest ${result.target}`);
-            return result.spec;
+            debugUtils.log(`Using ${spec.name}@${spec.range} as defined in project manifest ${result.target}`);
+            return spec;
           }
         }
       }

sources/commands/Base.ts

@@ -19,7 +19,7 @@ export abstract class BaseCommand extends Command<Context> {
           throw new UsageError(`The local project doesn't feature a 'packageManager' field - please specify the package manager to pack, or update the manifest to reference it`);
 
         default: {
-          return [lookup.spec];
+          return [lookup.getSpec()];
         }
       }
     }

sources/commands/deprecated/Prepare.ts

@@ -42,7 +42,7 @@ export class PrepareCommand extends Command<Context> {
           throw new UsageError(`The local project doesn't feature a 'packageManager' field - please specify the package manager to pack, or update the manifest to reference it`);
 
         default: {
-          specs.push(lookup.spec);
+          specs.push(lookup.getSpec());
         }
       }
     }

sources/specUtils.ts

@@ -75,7 +75,7 @@ export async function setLocalPackageManager(cwd: string, info: PreparedPackageM
 export type LoadSpecResult =
     | {type: `NoProject`, target: string}
     | {type: `NoSpec`, target: string}
-    | {type: `Found`, target: string, spec: Descriptor};
+    | {type: `Found`, target: string, getSpec: () => Descriptor};
 
 export async function loadSpec(initialCwd: string): Promise<LoadSpecResult> {
   let nextCwd = initialCwd;
@@ -124,6 +124,7 @@ export async function loadSpec(initialCwd: string): Promise<LoadSpecResult> {
   return {
     type: `Found`,
     target: selection.manifestPath,
-    spec: parseSpec(rawPmSpec, path.relative(initialCwd, selection.manifestPath)),
+    // Lazy-loading it so we do not throw errors on commands that do not need valid spec.
+    getSpec: () => parseSpec(rawPmSpec, path.relative(initialCwd, selection.manifestPath)),
   };
 }

tests/Use.test.ts

@@ -70,4 +70,50 @@ describe(`UseCommand`, () => {
       });
     });
   });
+
+  describe(`should not care if packageManager is set to an invalid value`, () => {
+    for (const {description, packageManager} of [
+      {
+        description: `when a version range is given`,
+        packageManager: `yarn@1.x`,
+      },
+      {
+        description: `when only the pm name is given`,
+        packageManager: `yarn`,
+      },
+      {
+        description: `when the version is missing`,
+        packageManager: `yarn@`,
+      },
+      {
+        description: `when the field is not a string`,
+        packageManager: [],
+      },
+    ]) {
+      it(description, async () => {
+        await xfs.mktempPromise(async cwd => {
+          await xfs.writeJsonPromise(ppath.join(cwd, `package.json`), {
+            packageManager,
+            license: `MIT`, // To avoid warning
+          });
+
+          await expect(runCli(cwd, [`use`, `yarn@1.22.4`])).resolves.toMatchObject({
+            exitCode: 0,
+            stderr: ``,
+            stdout: expect.stringMatching(/^Installing yarn@1\.22\.4 in the project\.\.\.\n\nyarn install v1\.22\.4\ninfo No lockfile found\.\n(.*\n)+Done in \d+\.\d+s\.\n$/),
+          });
+
+          await expect(xfs.readJsonPromise(ppath.join(cwd, `package.json`))).resolves.toMatchObject({
+            packageManager: `yarn@1.22.4+sha512.a1833b862fe52169bd6c2a033045a07df5bc6a23595c259e675fed1b2d035ab37abe6ce309720abb6636d68f03615054b6292dc0a70da31c8697fda228b50d18`,
+          });
+
+          await expect(runCli(cwd, [`yarn`, `--version`])).resolves.toMatchObject({
+            exitCode: 0,
+            stdout: `1.22.4\n`,
+            stderr: ``,
+          });
+        });
+      });
+    }
+  });
 });