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| 1 # I just need to fix the compile! |
| 2 |
| 3 To locally run closure compiler like the bots, do this: |
| 4 |
| 5 ``` |
| 6 cd $CHROMIUM_SRC |
| 7 # sudo apt-get install openjdk-7-jre # may be required |
| 8 GYP_GENERATORS=ninja tools/gyp/gyp --depth . third_party/closure_compiler/compil
ed_resources.gyp |
| 9 ninja -C out/Default |
| 10 ``` |
| 11 |
| 12 # Background |
| 13 |
| 14 In C++ and Java, compiling the code gives you _some_ level of protection against
misusing variables based on their type information. JavaScript is loosely type
d and therefore doesn't offer this safety. This makes writing JavaScript more e
rror prone as it's _one more thing_ to mess up. |
| 15 |
| 16 Because having this safety is handy, Chrome now has a way to optionally typechec
k your JavaScript and produce compiled output with [Closure Compiler](https://de
velopers.google.com/closure/compiler/). |
| 17 |
| 18 See also: [the design doc](https://docs.google.com/a/chromium.org/document/d/1Ee
9ggmp6U-lM-w9WmxN5cSLkK9B5YAq14939Woo-JY0/edit). |
| 19 |
| 20 # Assumptions |
| 21 |
| 22 A working Chrome checkout. See here: http://www.chromium.org/developers/how-tos
/get-the-code |
| 23 |
| 24 # Typechecking Your Javascript |
| 25 |
| 26 So you'd like to compile your JavaScript! |
| 27 |
| 28 Maybe you're working on a page that looks like this: |
| 29 |
| 30 ``` |
| 31 <script src="other_file.js"></script> |
| 32 <script src="my_product/my_file.js"></script> |
| 33 ``` |
| 34 |
| 35 Where `other_file.js` contains: |
| 36 |
| 37 ``` |
| 38 var wit = 100; |
| 39 |
| 40 // ... later on, sneakily ... |
| 41 |
| 42 wit += ' IQ'; // '100 IQ' |
| 43 ``` |
| 44 |
| 45 and `src/my_product/my_file.js` contains: |
| 46 |
| 47 ``` |
| 48 /** @type {number} */ var mensa = wit + 50; |
| 49 alert(mensa); // '100 IQ50' instead of 150 |
| 50 ``` |
| 51 |
| 52 In order to check that our code acts as we'd expect, we can create a |
| 53 |
| 54 ``` |
| 55 my_project/compiled_resources.gyp |
| 56 ``` |
| 57 |
| 58 with the contents: |
| 59 |
| 60 ``` |
| 61 # Copyright 2015 The Chromium Authors. All rights reserved. |
| 62 # Use of this source code is governed by a BSD-style license that can be |
| 63 # found in the LICENSE file. |
| 64 { |
| 65 'targets': [ |
| 66 { |
| 67 'target_name': 'my_file', # file name without ".js" |
| 68 |
| 69 'variables': { # Only use if necessary (no need to specify empty lists). |
| 70 'depends': [ |
| 71 'other_file.js', # or 'other_project/compiled_resources.gyp:target', |
| 72 ], |
| 73 'externs': [ |
| 74 '<(CLOSURE_DIR)/externs/any_needed_externs.js' # e.g. chrome.send(),
chrome.app.window, etc. |
| 75 ], |
| 76 }, |
| 77 |
| 78 'includes': ['../third_party/closure_compiler/compile_js.gypi'], |
| 79 }, |
| 80 ], |
| 81 } |
| 82 ``` |
| 83 |
| 84 You should get results like: |
| 85 |
| 86 ``` |
| 87 (ERROR) Error in: my_project/my_file.js |
| 88 ## /my/home/chromium/src/my_project/my_file.js:1: ERROR - initializing variable |
| 89 ## found : string |
| 90 ## required: number |
| 91 ## /** @type {number} */ var mensa = wit + 50; |
| 92 ## ^ |
| 93 ``` |
| 94 |
| 95 Yay! We can easily find our unexpected type errors and write less error-prone c
ode! |
| 96 |
| 97 # Continuous Checking |
| 98 |
| 99 To compile your code on every commit, add a line to [third\_party/closure\_compi
ler/compiled\_resources.gyp](https://code.google.com/p/chromium/codesearch#chrom
ium/src/third_party/closure_compiler/compiled_resources.gyp&sq=package:chromium&
type=cs) like this: |
| 100 |
| 101 ``` |
| 102 { |
| 103 'targets': [ |
| 104 { |
| 105 'target_name': 'compile_all_resources', |
| 106 'dependencies': [ |
| 107 # ... other projects ... |
| 108 ++ '../my_project/compiled_resources.gyp:*', |
| 109 ], |
| 110 } |
| 111 ] |
| 112 } |
| 113 ``` |
| 114 |
| 115 and the [Closure compiler bot](http://build.chromium.org/p/chromium.fyi/builders
/Closure%20Compilation%20Linux) will [re-]compile your code whenever relevant .j
s files change. |
| 116 |
| 117 # Using Compiled JavaScript |
| 118 |
| 119 Compiled JavaScript is output in src/out/<Debug|Release>/gen/closure/my\_project
/my\_file.js along with a source map for use in debugging. In order to use the c
ompiled JavaScript, we can create a |
| 120 |
| 121 ``` |
| 122 my_project/my_project_resources.gpy |
| 123 ``` |
| 124 |
| 125 with the contents: |
| 126 |
| 127 ``` |
| 128 # Copyright 2015 The Chromium Authors. All rights reserved. |
| 129 # Use of this source code is governed by a BSD-style license that can be |
| 130 # found in the LICENSE file. |
| 131 |
| 132 { |
| 133 'targets': [ |
| 134 { |
| 135 # GN version: //my_project/resources |
| 136 'target_name': 'my_project_resources', |
| 137 'type': 'none', |
| 138 'variables': { |
| 139 'grit_out_dir': '<(SHARED_INTERMEDIATE_DIR)/my_project', |
| 140 'my_file_gen_js': '<(SHARED_INTERMEDIATE_DIR)/closure/my_project/my_file
.js', |
| 141 }, |
| 142 'actions': [ |
| 143 { |
| 144 # GN version: //my_project/resources:my_project_resources |
| 145 'action_name': 'generate_my_project_resources', |
| 146 'variables': { |
| 147 'grit_grd_file': 'resources/my_project_resources.grd', |
| 148 'grit_additional_defines': [ |
| 149 '-E', 'my_file_gen_js=<(my_file_gen_js)', |
| 150 ], |
| 151 }, |
| 152 'includes': [ '../build/grit_action.gypi' ], |
| 153 }, |
| 154 ], |
| 155 'includes': [ '../build/grit_target.gypi' ], |
| 156 }, |
| 157 ], |
| 158 } |
| 159 ``` |
| 160 |
| 161 The variables can also be defined in an existing .gyp file if appropriate. The v
ariables can then be used in to create a |
| 162 |
| 163 ``` |
| 164 my_project/my_project_resources.grd |
| 165 ``` |
| 166 |
| 167 with the contents: |
| 168 |
| 169 ``` |
| 170 <?xml version="1.0" encoding="utf-8"?> |
| 171 <grit-part> |
| 172 <include name="IDR_MY_FILE_GEN_JS" file="${my_file_gen_js}" use_base_dir="fals
e" type="BINDATA" /> |
| 173 </grit-part> |
| 174 ``` |
| 175 |
| 176 In your C++, the resource can be retrieved like this: |
| 177 ``` |
| 178 base::string16 my_script = |
| 179 base::UTF8ToUTF16( |
| 180 ResourceBundle::GetSharedInstance() |
| 181 .GetRawDataResource(IDR_MY_FILE_GEN_JS) |
| 182 .as_string()); |
| 183 ``` |
| 184 |
| 185 # Debugging Compiled JavaScript |
| 186 |
| 187 Along with the compiled JavaScript, a source map is created: src/out/<Debug|Rele
ase>/gen/closure/my\_project/my\_file.js.map |
| 188 |
| 189 Chrome DevTools has built in support for working with source maps: [https://deve
loper.chrome.com/devtools/docs/javascript-debugging#source-maps](https://develop
er.chrome.com/devtools/docs/javascript-debugging#source-maps) |
| 190 |
| 191 In order to use the source map, you must first manually edit the path to the 'so
urces' in the .js.map file that was generated. For example, if the source map lo
oks like this: |
| 192 ``` |
| 193 { |
| 194 "version":3, |
| 195 "file":"/tmp/gen/test_script.js", |
| 196 "lineCount":1, |
| 197 "mappings":"A,aAAA,IAAIA,OAASA,QAAQ,EAAG,CACtBC,KAAA,CAAM,OAAN,CADsB;", |
| 198 "sources":["/tmp/tmp70_QUi"], |
| 199 "names":["fooBar","alert"] |
| 200 } |
| 201 ``` |
| 202 |
| 203 sources should be changed to: |
| 204 ``` |
| 205 ... |
| 206 "sources":["/tmp/test_script.js"], |
| 207 ... |
| 208 ``` |
| 209 |
| 210 In your browser, the source map can be loaded through the Chrome DevTools contex
t menu that appears when you right click in the compiled JavaScript source body.
A dialog will pop up prompting you for the path to the source map file. Once th
e source map is loaded, the uncompiled version of the JavaScript will appear in
the Sources panel on the left. You can set break points in the uncompiled versio
n to help debug; behind the scenes Chrome will still be running the compiled ver
sion of the JavaScript. |
| 211 |
| 212 # Additional Arguments |
| 213 |
| 214 compile\_js.gypi accepts an optional script\_args variable, which passes additio
nal arguments to compile.py, as well as an optional closure\_args variable, whic
h passes additional arguments to the closure compiler. You may also override the
disabled\_closure\_args for more strict compilation. |
| 215 |
| 216 For example, if you would like to specify multiple sources, strict compilation,
and an output wrapper, you would create a |
| 217 |
| 218 ``` |
| 219 my_project/compiled_resources.gyp |
| 220 ``` |
| 221 |
| 222 with contents similar to this: |
| 223 ``` |
| 224 # Copyright 2015 The Chromium Authors. All rights reserved. |
| 225 # Use of this source code is governed by a BSD-style license that can be |
| 226 # found in the LICENSE file. |
| 227 { |
| 228 'targets' :[ |
| 229 { |
| 230 'target_name': 'my_file', |
| 231 'variables': { |
| 232 'source_files': [ |
| 233 'my_file.js', |
| 234 'my_file2.js', |
| 235 ], |
| 236 'script_args': ['--no-single-file'], # required to process multiple file
s at once |
| 237 'closure_args': [ |
| 238 'output_wrapper=\'(function(){%output%})();\'', |
| 239 'jscomp_error=reportUnknownTypes', # the following three provide m
ore strict compilation |
| 240 'jscomp_error=duplicate', |
| 241 'jscomp_error=misplacedTypeAnnotation', |
| 242 ], |
| 243 'disabled_closure_args': [], # remove the disabled closure args for more
strict compilation |
| 244 }, |
| 245 'includes': ['../third_party/closure_compiler/compile_js.gypi'], |
| 246 }, |
| 247 ], |
| 248 } |
| 249 ``` |
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