default allow-empty-coverage if disable-coverage set

Fix: #1001

src/config/src/index.ts

@@ -125,7 +125,14 @@ export class TapConfig<C extends ConfigSet = BaseConfigSet> {
    * Get a configuration value, as we currently know it
    */
   get<K extends keyof OptionsResults<C>>(k: K): OptionsResults<C>[K] {
-    return this.parse().values[k]
+    const value = this.parse().values[k]
+    // special case: if --disable-coverage is set, then default
+    // --allow-empty-coverage to true, so we don't get unuseful failures.
+    if (k === 'allow-empty-coverage' && value === undefined) {
+      const disabled = this.get('disable-coverage')
+      if (disabled) return true as OptionsResults<C>[K]
+    }
+    return value
   }
 
   /**

src/config/src/jack.ts

@@ -463,8 +463,9 @@ export default jack({
       description: `Do not generate code coverage information for the test run.
 
                     This will always result in a \`# No coverage generated\`
-                    message being printed, and will cause the test run to exit
-                    in error unless \`allow-empty-coverage\` is also set.
+                    message being printed. If this flag is set, then
+                    \`--allow-empty-coverage\` will default to \`true\`,
+                    because we do not expect to get any coverage.
 
                     WARNING: tests that do not produce coverage are
                     untrustworthy. This should only be used when coverage is

src/config/tap-snapshots/test/jack.ts.test.cjs

@@ -131,7 +131,7 @@ Object {
     "description": String(
       Do not generate code coverage information for the test run.
       
-      This will always result in a \`# No coverage generated\` message being printed, and will cause the test run to exit in error unless \`allow-empty-coverage\` is also set.
+      This will always result in a \`# No coverage generated\` message being printed. If this flag is set, then \`--allow-empty-coverage\` will default to \`true\`, because we do not expect to get any coverage.
       
       WARNING: tests that do not produce coverage are untrustworthy. This should only be used when coverage is being generated and tracked by some other mechanism.
     ),

src/config/test/index.ts

@@ -892,3 +892,20 @@ t.test('load file from env.TAP_RCFILE', async t => {
     }
   }
 })
+
+t.test('default allow-empty-coverage when disable-coverage set', async t => {
+  const dir = t.testdir({
+    '.taprc': `
+disable-coverage: true
+`,
+  })
+  const cwd = process.cwd()
+  t.teardown(() => process.chdir(cwd))
+  process.chdir(dir)
+  const { TapConfig } = await t.mockImport<
+    typeof import('../dist/esm/index.js')
+  >('../dist/esm/index.js')
+  const c = await TapConfig.load()
+  t.equal(c.get('disable-coverage'), true)
+  t.equal(c.get('allow-empty-coverage'), true)
+})