compiler: automate regeneration of prelude (#784)

This is a rebase of #765.

Whilst rebasing #669 I fell into a similar trap to #775 (#775 (comment)),
by forgetting to commit the manually minified prelude.

Then going through the manual process of manually minifying the prelude I wasted a whole load of
time installing goexec, missing something the first time etc, issues that this PR addresses by
automating the process, as previously discussed (#765 (comment)).

circle.yml

@@ -10,10 +10,13 @@ dependencies:
   post:
     - mv ./gopherjs $HOME/bin
     - npm install --global node-gyp
+    - npm install # install our (dev) dependencies from package.json
     - cd node-syscall && node-gyp rebuild && mkdir -p ~/.node_libraries/ && cp build/Release/syscall.node ~/.node_libraries/syscall.node
 
 test:
   override:
+    - go generate github.com/gopherjs/gopherjs/compiler/prelude
+    - diff -u <(echo -n) <(git status --porcelain)
     - diff -u <(echo -n) <(gofmt -d .)
     - go tool vet *.go                                                   # Go package in root directory.
     - for d in */; do echo $d; done | grep -v tests/ | grep -v third_party/ | xargs go tool vet # All subdirectories except "tests", "third_party".

compiler/prelude/genmin.go

@@ -0,0 +1,63 @@
+// +build ignore
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"go/build"
+	"io/ioutil"
+	"log"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
+	"github.com/gopherjs/gopherjs/compiler/prelude"
+)
+
+func main() {
+	if err := run(); err != nil {
+		log.Fatalln(err)
+	}
+}
+
+func run() error {
+	bpkg, err := build.Import("github.com/gopherjs/gopherjs", "", build.FindOnly)
+	if err != nil {
+		return fmt.Errorf("failed to locate path for github.com/gopherjs/gopherjs: %v", err)
+	}
+
+	preludeDir := filepath.Join(bpkg.Dir, "compiler", "prelude")
+
+	args := []string{
+		filepath.Join(bpkg.Dir, "node_modules", ".bin", "uglifyjs"),
+		"--config-file",
+		filepath.Join(preludeDir, "uglifyjs_options.json"),
+	}
+
+	stderr := new(bytes.Buffer)
+	cmd := exec.Command(args[0], args[1:]...)
+	cmd.Stdin = strings.NewReader(prelude.Prelude)
+	cmd.Stderr = stderr
+
+	out, err := cmd.Output()
+	if err != nil {
+		return fmt.Errorf("failed to run %v: %v\n%s", strings.Join(args, " "), err, stderr.String())
+	}
+
+	fn := "prelude_min.go"
+
+	outStr := fmt.Sprintf(`// Code generated by genmin; DO NOT EDIT.
+
+package prelude
+
+// Minified is an uglifyjs-minified version of Prelude.
+const Minified = %q
+`, out)
+
+	if err := ioutil.WriteFile(fn, []byte(outStr), 0644); err != nil {
+		return fmt.Errorf("failed to write to %v: %v", fn, err)
+	}
+
+	return nil
+}

compiler/prelude/uglifyjs_options.json

@@ -0,0 +1,98 @@
+{
+	"compress": {
+		"arrows": true,
+		"booleans": true,
+		"collapse_vars": true,
+		"comparisons": true,
+		"computed_props": true,
+		"conditionals": true,
+		"dead_code": true,
+		"drop_console": false,
+		"drop_debugger": true,
+		"ecma": 5,
+		"evaluate": true,
+		"expression": false,
+		"global_defs": {},
+		"hoist_funs": false,
+		"hoist_props": true,
+		"hoist_vars": false,
+		"ie8": false,
+		"if_return": true,
+		"inline": true,
+		"join_vars": true,
+		"keep_classnames": false,
+		"keep_fargs": true,
+		"keep_fnames": false,
+		"keep_infinity": false,
+		"loops": true,
+		"negate_iife": true,
+		"passes": 1,
+		"properties": true,
+		"pure_funcs": null,
+		"pure_getters": "strict",
+		"reduce_funcs": true,
+		"reduce_vars": true,
+		"sequences": true,
+		"side_effects": true,
+		"switches": true,
+		"top_retain": null,
+		"toplevel": false,
+		"typeofs": true,
+		"unsafe": false,
+		"unsafe_Function": false,
+		"unsafe_arrows": false,
+		"unsafe_comps": false,
+		"unsafe_math": false,
+		"unsafe_methods": false,
+		"unsafe_proto": false,
+		"unsafe_regexp": false,
+		"unsafe_undefined": false,
+		"unused": true,
+		"warnings": false
+	},
+	"mangle": {
+		"eval": false,
+		"ie8": false,
+		"keep_classnames": false,
+		"keep_fnames": false,
+		"properties": false,
+		"reserved": [],
+		"safari10": false,
+		"toplevel": false
+	},
+	"output": {
+		"ascii_only": false,
+		"beautify": false,
+		"bracketize": false,
+		"comments": "/@license|@preserve|^!/",
+		"ecma": 5,
+		"ie8": false,
+		"indent_level": 4,
+		"indent_start": 0,
+		"inline_script": true,
+		"keep_quoted_props": false,
+		"max_line_len": false,
+		"preamble": null,
+		"preserve_line": false,
+		"quote_keys": false,
+		"quote_style": 0,
+		"safari10": false,
+		"semicolons": true,
+		"shebang": true,
+		"source_map": null,
+		"webkit": false,
+		"width": 80,
+		"wrap_iife": false
+	},
+	"parse": {
+		"bare_returns": false,
+		"ecma": 8,
+		"expression": false,
+		"filename": null,
+		"html5_comments": true,
+		"shebang": true,
+		"strict": false,
+		"toplevel": null
+	},
+	"wrap": false
+}

package.json

@@ -0,0 +1,6 @@
+{
+  "name": "gopherjs",
+  "devDependencies": {
+    "uglify-es": "3.3.9"
+  }
+}