Add a swc transform for removal of console.* calls.

examples/remove-console/.gitignore

@@ -0,0 +1,34 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.js
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# local env files
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+# vercel
+.vercel

examples/remove-console/README.md

@@ -0,0 +1,27 @@
+# Remove Console Example
+
+This example shows how to use the `removeConsole` config option to remove all `console.*` calls.
+
+## Preview
+
+Preview the example live on [StackBlitz](http://stackblitz.com/):
+
+[![Open in StackBlitz](https://developer.stackblitz.com/img/open_in_stackblitz.svg)](https://stackblitz.com/github/vercel/next.js/tree/canary/examples/remove-console)
+
+## Deploy your own
+
+Deploy the example using [Vercel](https://vercel.com?utm_source=github&utm_medium=readme&utm_campaign=next-example):
+
+[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https://github.com/vercel/next.js/tree/canary/examples/remove-console&project-name=remove-console&repository-name=remove-console)
+
+## How to use
+
+Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init) or [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/) to bootstrap the example:
+
+```bash
+npx create-next-app --example remove-console remove-console-app
+# or
+yarn create next-app --example remove-console remove-console-app
+```
+
+Deploy it to the cloud with [Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

examples/remove-console/next.config.js

@@ -0,0 +1,9 @@
+module.exports = {
+  experimental: {
+    removeConsole: {
+      exclude: ['error'],
+    },
+    // Uncomment this to suppress all logs.
+    // removeConsole: true,
+  },
+}

examples/remove-console/package.json

@@ -0,0 +1,13 @@
+{
+  "private": true,
+  "scripts": {
+    "dev": "next dev",
+    "build": "next build",
+    "start": "next start"
+  },
+  "dependencies": {
+    "next": "latest",
+    "react": "^17.0.2",
+    "react-dom": "^17.0.2"
+  }
+}

examples/remove-console/pages/index.js

@@ -0,0 +1,10 @@
+const Index = () => (
+  <div>
+    <p>The console should be empty.</p>
+  </div>
+)
+
+console.log('log from index.js')
+console.error('error log from index.js')
+
+export default Index

packages/next/build/swc/options.js

@@ -66,6 +66,7 @@ function getBaseSWCOptions({
           displayName: Boolean(development),
         }
       : null,
+    removeConsole: nextConfig?.experimental?.removeConsole,
   }
 }
 

packages/next/build/swc/src/lib.rs

@@ -60,7 +60,9 @@ pub mod minify;
 pub mod next_dynamic;
 pub mod next_ssg;
 pub mod page_config;
+pub mod remove_console;
 pub mod styled_jsx;
+mod top_level_binding_collector;
 mod transform;
 mod util;
 
@@ -87,6 +89,9 @@ pub struct TransformOptions {
 
     #[serde(default)]
     pub styled_components: Option<styled_components::Config>,
+
+    #[serde(default)]
+    pub remove_console: Option<remove_console::Config>,
 }
 
 pub fn custom_before_pass(file: Arc<SourceFile>, opts: &TransformOptions) -> impl Fold {
@@ -113,7 +118,12 @@ pub fn custom_before_pass(file: Arc<SourceFile>, opts: &TransformOptions) -> imp
         Optional::new(
             page_config::page_config(opts.is_development, opts.is_page_file),
             !opts.disable_page_config
-        )
+        ),
+        match &opts.remove_console {
+            Some(config) if config.truthy() =>
+                Either::Left(remove_console::remove_console(config.clone())),
+            _ => Either::Right(noop()),
+        },
     )
 }
 

packages/next/build/swc/src/remove_console.rs

@@ -0,0 +1,146 @@
+use serde::Deserialize;
+use swc_atoms::JsWord;
+use swc_common::collections::AHashSet;
+use swc_common::DUMMY_SP;
+use swc_ecmascript::ast::*;
+use swc_ecmascript::utils::ident::IdentLike;
+use swc_ecmascript::utils::Id;
+use swc_ecmascript::visit::{noop_fold_type, Fold, FoldWith};
+
+use crate::top_level_binding_collector::collect_top_level_decls;
+
+#[derive(Clone, Debug, Deserialize)]
+#[serde(untagged)]
+pub enum Config {
+    All(bool),
+    WithOptions(Options),
+}
+
+impl Config {
+    pub fn truthy(&self) -> bool {
+        match self {
+            Config::All(b) => *b,
+            Config::WithOptions(_) => true,
+        }
+    }
+}
+
+#[derive(Clone, Debug, Deserialize)]
+pub struct Options {
+    #[serde(default)]
+    pub exclude: Vec<JsWord>,
+}
+
+struct RemoveConsole {
+    exclude: Vec<JsWord>,
+    bindings: Vec<AHashSet<Id>>,
+    in_function_params: bool,
+}
+
+impl RemoveConsole {
+    fn is_global_console(&self, ident: &Ident) -> bool {
+        &ident.sym == "console"
+            && self
+                .bindings
+                .iter()
+                .find(|x| x.contains(&ident.to_id()))
+                .is_none()
+    }
+
+    fn should_remove_call(&mut self, n: &CallExpr) -> bool {
+        let callee = &n.callee;
+        let member_expr = match callee {
+            ExprOrSuper::Expr(e) => match &**e {
+                Expr::Member(m) => m,
+                _ => return false,
+            },
+            _ => return false,
+        };
+
+        // Don't attempt to evaluate computed properties.
+        if member_expr.computed {
+            return false;
+        }
+
+        // Only proceed if the object is the global `console` object.
+        match &member_expr.obj {
+            ExprOrSuper::Expr(e) => match &**e {
+                Expr::Ident(i) if self.is_global_console(i) => {}
+                _ => return false,
+            },
+            _ => return false,
+        }
+
+        // Check if the property is requested to be excluded.
+        // Here we do an O(n) search on the list of excluded properties because the size
+        // should be small.
+        match &*member_expr.prop {
+            Expr::Ident(i) if self.exclude.iter().find(|x| **x == i.sym).is_none() => {}
+            _ => return false,
+        }
+
+        true
+    }
+}
+
+impl Fold for RemoveConsole {
+    noop_fold_type!();
+
+    fn fold_stmt(&mut self, stmt: Stmt) -> Stmt {
+        match &stmt {
+            Stmt::Expr(e) => match &*e.expr {
+                Expr::Call(c) => {
+                    if self.should_remove_call(c) {
+                        return Stmt::Empty(EmptyStmt { span: DUMMY_SP });
+                    }
+                }
+                _ => {}
+            },
+            _ => {}
+        }
+        stmt.fold_children_with(self)
+    }
+
+    fn fold_function(&mut self, mut func: Function) -> Function {
+        self.in_function_params = true;
+        let mut new_params: AHashSet<Id> = AHashSet::default();
+        for param in &func.params {
+            new_params.extend(collect_top_level_decls(param));
+        }
+        self.in_function_params = false;
+
+        self.bindings.push(new_params);
+        self.bindings.push(collect_top_level_decls(&func));
+        func.body = func.body.fold_with(self);
+        self.bindings.pop().unwrap();
+        self.bindings.pop().unwrap();
+        func
+    }
+
+    fn fold_module(&mut self, module: Module) -> Module {
+        self.bindings.push(collect_top_level_decls(&module));
+        let m = module.fold_children_with(self);
+        self.bindings.pop().unwrap();
+        m
+    }
+
+    fn fold_script(&mut self, script: Script) -> Script {
+        self.bindings.push(collect_top_level_decls(&script));
+        let s = script.fold_with(self);
+        self.bindings.pop().unwrap();
+        s
+    }
+}
+
+pub fn remove_console(config: Config) -> impl Fold {
+    let exclude = match config {
+        Config::WithOptions(x) => x.exclude,
+        _ => vec![],
+    };
+    let remover = RemoveConsole {
+        exclude,
+        bindings: Default::default(),
+        in_function_params: false,
+    };
+    remover
+}