Add triggersRerun setting to control fingerprint inheritance

CHANGELOG.md

@@ -15,6 +15,52 @@ Versioning](https://semver.org/spec/v2.0.0.html).
   or when another script that depends on it is ready to run. A service is stopped
   when all scripts that depend on it have finished, or when Wireit is exited.
 
+- Added `"triggersRerun": false` setting to dependencies.
+
+  By default, the fingerprint of a script includes the fingerprints of its
+  dependencies. This means a script will re-run whenever one of its dependencies
+  re-runs, even if the output produced by the dependency didn't actually change.
+
+  Now, if a dependency is annotated with `"triggersRerun": false`, then the
+  fingerprint of that dependency will no longer be included in the script's own
+  fingerprint. This means a script won't neccessarily re-run just because a
+  dependency re-ran — though Wireit will still always run the dependency first
+  if it is not up-to-date.
+
+  Using `"triggersRerun": false` can result in faster builds thanks to fewer
+  re-runs, but it is very important to specify all of the input files generated
+  by the dependency which the script depends on in the `files` array.
+
+  Example:
+
+  ```json
+  {
+    "wireit": {
+      "build": {
+        "command": "tsc",
+        "files": ["tsconfig.json", "src/**/*.ts"],
+        "output": "lib/**",
+      },
+      "bundle": {
+        "command": "rollup -c",
+        "files": ["rollup.config.json", "lib/**/*.js", "!lib/test"],
+        "output": "dist/bundle.js",
+        "dependencies": {
+          [
+            "script": "build",
+            "triggersRerun": false
+          ]
+        }
+      }
+    }
+  }
+  ```
+
+### Changed
+
+- Added string length > 0 requirement to the `command`, `dependencies`, `files`,
+  `output`, and `packageLocks` properties in `schema.json`.
+
 ### Fixed
 
 - Fixed memory leak in watch mode.

README.md

@@ -23,6 +23,7 @@
 - [Dependencies](#dependencies)
   - [Vanilla scripts](#vanilla-scripts)
   - [Cross-package dependencies](#cross-package-dependencies)
+  - [Triggers re-run](#triggers-re-run)
 - [Parallelism](#parallelism)
 - [Extra arguments](#extra-arguments)
 - [Input and output files](#input-and-output-files)
@@ -168,6 +169,78 @@ workspaces, as well as in other kinds of monorepos.
 }
 ```
 
+### Triggers re-run
+
+By default, whenever a dependency runs, the script that depends on it will be
+marked stale and need to re-run too — regardless of whether the dependency
+actually produced new or relevant output.
+
+This is a safe default because it means you aren't required to specify the input
+files for every script when those input files are generated by a dependency.
+However, it comes with the tradeoff that scripts will sometimes re-run even when
+none of their input files changed.
+
+To change this behavior and further optimize your build, you can use the
+`triggersRerun` setting to tell Wireit that all of the input files needed from
+a dependency are declared in the `files` array. Now, Wireit won't assume that a
+script was stale just because its dependency ran.
+
+To enable this setting, create an object for your dependency instead of a plain
+string, and set `triggersRerun` to `false`:
+
+```json
+{
+  "wireit": {
+    "A": {
+      "dependencies": [
+        {
+          "script": "B",
+          "triggersRerun": false
+        }
+      ]
+    }
+  }
+}
+```
+
+In the following example, `bundle` has a dependency on `build` with
+`triggersRerun: false`. Importantly, it also includes `lib/**/*.js` in its
+`files` array, which are the specific outputs from `tsc` that `rollup` consumes.
+Including these input files wasn't neccessary before, but with
+`triggersRerun: false` it is now critical.
+
+```json
+{
+  "scripts": {
+    "build": "wireit",
+    "bundle": "wireit"
+  },
+  "wireit": {
+    "build": {
+      "command": "tsc",
+      "files": ["src/**/*.ts", "tsconfig.json"],
+      "output": ["lib/**"]
+    },
+    "bundle": {
+      "command": "rollup -c",
+      "dependencies": [
+        {
+          "script": "build",
+          "triggersRerun": false
+        }
+      ],
+      "files": ["rollup.config.json", "lib/**/*.js", "!lib/test"],
+      "output": ["dist/bundle.js"]
+    }
+  }
+}
+```
+
+The advantage of this configuration is that if `tsc` re-runs but doesn't produce
+different `.js` files (for example, if it only produced different `.d.ts`
+files), then `rollup` won't need to re-run. We've also excluded the `lib/test`
+directory, because we know test files aren't included in our bundles.
+
 ## Parallelism
 
 Wireit will run scripts in parallel whenever it is safe to do so according to
@@ -408,26 +481,45 @@ expected to exit by itself, set `"service": true`.
       "command": "node my-server.js",
       "service": true,
       "files": ["server-config.json"],
-      "dependencies": ["build:server", "build:assets"]
+      "dependencies": [
+        "build:server",
+        {
+          "script": "build:assets",
+          "triggersRerun": false
+        }
+      ]
     }
   }
 }
 ```
 
+### Service lifetime
+
 If a service is run _directly_ (e.g. `npm run serve`), then it will stay running
 until the user kills Wireit (e.g. `Ctrl-C`).
 
 If a service is a _dependency_ of one or more other scripts, then it will start
 up before any depending script runs, and will shut down after all depending
 scripts finish.
 
+### Service restarts
+
 In watch mode, a service will be restarted whenever one of its input files or
-dependencies change.
+dependencies change, except for dependencies with
+[`triggersRerun: false`](#re-run-on-change).
+
+Use `triggersRerun: false` when the output of a dependency is read dynamically
+for each request handled by the service. For example, the static assets of a web
+server can often be annotated with `triggersRerun: false`.
+
+### Service output
 
 Services cannot have `output` files, because there is no way for Wireit to know
-when a service has finished writing its output. If you have a service that
-produces output, you should define a non-service script that depends on it, and
-which exits when the service's output is complete.
+when a service has finished writing its output.
+
+If you have a service that produces output, you should define a _non-service_
+script that depends on it, and which exits when the service's output is
+complete.
 
 ## Failures and errors
 

schema.json

@@ -14,33 +14,57 @@
           },
           "command": {
             "markdownDescription": "The command to run.\n\nThis is a shell command that will be executed, with all binaries from npm dependencies and devDependencies available.\n\nFor example:\n\n```json\n\"command\": \"tsc\"\n```\n\nFor more info, see https://docs.npmjs.com/cli/v8/using-npm/scripts#environment",
-            "type": "string"
+            "type": "string",
+            "minLength": 1
           },
           "dependencies": {
             "markdownDescription": "Other npm scripts that will run before this one.\n\nThese scripts do not have to use wireit.\n\nDependencies can refer to scripts in other npm packages by using a relative path with the syntax `<relative-path>:<script-name>`. All cross-package dependencies should start with a `\".\"`. Cross-package dependencies work well for npm workspaces, as well as in other kinds of monorepos.\n\nFor example:\n\n```json\n\"dependencies\": [\n  \"build\",\n  \"./packages/foo:build\"\n]\n```\n\nFor more info, see https://github.com/google/wireit#dependencies",
             "items": {
-              "type": "string"
+              "anyOf": [
+                {
+                  "type": "string",
+                  "minLength": 1
+                },
+                {
+                  "type": "object",
+                  "required": ["script"],
+                  "properties": {
+                    "script": {
+                      "markdownDescription": "The name of the script (see `dependencies`).",
+                      "type": "string",
+                      "minLength": 1
+                    },
+                    "triggersRerun": {
+                      "markdownDescription": "When `true` (the default), whenever this dependency runs, this script (the dependent) will be marked stale and need to re-run too, regardless of whether the dependency produced new or relevant output. When `false` Wireit won't assume that the dependent is stale just because the dependency ran. This can reduce unnecessary re-building (or restarting in the case of services) when `files` captures all of the relevant output of the dependency.\n\nFor more info, see https://github.com/google/wireit#re-run-on-change",
+                      "type": "boolean"
+                    }
+                  }
+                }
+              ]
             },
             "type": "array"
           },
           "files": {
             "markdownDescription": "The files that this script depends on.\n\nThese are the files that are watched when run with the `watch` argument. They are also used to determine if a script is stale or if its files and dependencies haven't changed and execution can be skipped.\n\nDon't specify `files` unless the array of files (and `dependencies`) are the only things that this script depends on. For example, a script that fetches data over the internet should not have a files array.\n\nThis should be a list of package-relative paths to files, or glob patterns. See https://github.com/google/wireit#glob-patterns for more info on the format of glob patterns.\n\nFor example:\n\n```json\n\"files\": [\n  \"src/**/*.ts\"\n]\n```",
             "items": {
-              "type": "string"
+              "type": "string",
+              "minLength": 1
             },
             "type": "array"
           },
           "output": {
             "markdownDescription": "The files that this script writes.\n\nThese are the files that are deleted before the script is executed (set `clean` to customize this behavior), and these are the files that are cached if `files` is specified.\n\nThis should be a list of package-relative paths to files, or glob patterns. See https://github.com/google/wireit#glob-patterns for more info on the format of glob patterns.\n\nFor example:\n\n```json\n\"output\": [\n  \"lib/**/*\",\n  \"!lib/bundle.js\"\n]\n```",
             "items": {
-              "type": "string"
+              "type": "string",
+              "minLength": 1
             },
             "type": "array"
           },
           "packageLocks": {
             "markdownDescription": "By default, Wireit automatically treats package-lock.json files in the package directory, plus all parent directories, as input files. This is useful because installing or upgrading your dependencies can affect the behavior of your scripts, so it's important to re-run them whenever your dependencies change.\n\nIf you are using an alternative package manager instead of npm, then your package lock files might be named something else.\n\nFor more info, see: https://github.com/google/wireit#package-locks",
             "items": {
-              "type": "string"
+              "type": "string",
+              "minLength": 1
             },
             "type": "array"
           },