# Hacking Some notes on modifying Chawan's code. ## Style Refer to the [NEP1](https://nim-lang.org/docs/nep1.html) for the basics. Also, try to keep the style of existing code. ### Casing Everything is camelCase. Enums are camelCase too, but the first part is an abbreviation of the type name. e.g. members of `SomeEnum` start with `se`. Exceptions: * Types/constants use PascalCase. enums in cssvalues use PascalCase too, to avoid name collisions. * Module-local templates use snake_case. * We keep style of external C libraries, which is often snake_case. * Chame is stuck with `SCREAMING_SNAKE_CASE` for its enums. This is unfortunate, but does not warrant an API breakage. Rationale: consistency. ### Wrapping 80 chars per line. Exceptions: URL comments. Rationale: makes it easier to edit in vi. ### Spacing No blank lines inside procedures (and other code blocks). A single blank line separates two procs, type defs, etc. If your proc doesn't fit on two 24-line screens, split it up into more procs instead of inserting blank lines. Exceptions: none. Occasionally a proc will get larger than two screens, and that's ok, but try to avoid it. Rationale: makes it easier to edit in vi. ### Param separation Semicolons, not commas. e.g. ```nim # Good proc foo(p1: int; p2, p3: string; p4 = true) # Bad proc bar(p1: int, p2, p3: string, p4 = true) ``` Rationale: makes it easier to edit in vi. ### Naming Prefer short names. Don't copy verbose naming from the standard. Rationale: we aren't a fruit company. ### Comments Comment what is not obvious, don't comment what is obvious. Whether something is obvious or not is left to your judgment. Don't paste standard prose into the code unless you're making a point. If you do, abridge the prose. Rationale: common sense, copyright. ## General coding tips and guidelines These are not hard rules, but please try to follow them unless the situation demands otherwise. ### Features to avoid List of Nim features/patterns that sound like a good idea but aren't, for non-obvious reasons. #### Exceptions Exceptions don't work well with JS embedding; use Result/Opt/Option instead. Note that these kill RVO, so if you're returning large objects, either make them `ref`, or use manual RVO (return bool, set var param). #### "result" variable The implicit "result" variable is great until you need to change the procedure signature or manually inline a proc. Avoid it when possible, except in short accumulator-style procedures. #### Implicit initialization Avoid. The correct way to create an object: ```nim let myObj = MyObject( param1: x, param2: y # if there's e.g. a param3 too, it's OK to leave it out and let it be # default initialized. ) ``` For arrays, use: ```nim var buf1 = array[1234, char].default # when you need 0-initialization var buf2 {.noinit.}: array[1234, char] # when you don't need 0-initialization ``` For primitive types, just set them to 0, "", etc. #### "out" parameters They crash the 1.6.14 compiler. Use "var" for now. #### Copying operations `substr` and `x[n..m]` copies. Try to use `toOpenArray` instead, which is a non-copying slice. (Obviously, you should use `substr` if you *need* to copy.) Note that `=` usually copies. If you're copying a large object a lot, you may want to set its type to `ref`. Beware of `pairs` on sequences of objects; it copies. Use `mypairs` if you don't need mutation, `mpairs` if you do: ```nim proc foo(objs: openArray[SomeObj]) = for i, obj in objs: # this copies. obj is of type "SomeObj". obj.bar(i) # import utils/twtstr to use mypairs. for i, obj in objs.mypairs: # doesn't copy. obj is of type "lent "SomeObj". obj.bar(i) for i, obj in objs.mpairs: # doesn't copy. obj is of type "var SomeObj". obj.i = i ``` #### Generic parameters for JS values Monoucha (our QuickJS wrapper) supports these, but they bloat code size and compile times. Similarly, `varargs[string]` works, but is less efficient than `varargs[JSValue]`. (The former is first converted into a seq, while the latter is just a slice.) Use `?ctx.fromJS(val, res)` on JSValues manually instead. ### Fixing cyclic imports In Nim, you can't have circular dependencies between modules. This gets unwieldy as the HTML/DOM/etc. specs are a huge cyclic OOP mess. The preferred workaround is global function pointer variables: ```nim # Forward declaration hack var forwardDeclImpl*: proc(window: Window; x, y: int) {.nimcall.} # in the other module: forwardDeclImpl = proc(window: Window; x, y: int) = # [...] ``` Don't forget to make it `.nimcall`, and to comment "Forward declaration hack" above. (Hopefully we can remove these once Nim supports cyclic module dependencies.) ## Debugging Note: following text assumes you are compiling in debug mode, i.e. `make TARGET=debug`. ### The universal debugger "eprint x, y" prints x, y to stderr, space separated. Normally you can view what you printed through the M-c M-c (escape + c twice) console. Except when you're printing from the pager, then do `cha [...] 2>a` and check the "a" file. Sometimes, printing to the console triggers a self-feeding loop of printing to the console. To avoid this, disable the console buffer: `cha [...] -o start.console-buffer=false 2>a`. Then check the "a" file. You can also inspect open buffers from the console. Note that you must run these *before* switching to the console buffer (i.e. before the second M-c), or it will show info about the console buffer. * `pager.process`: the current buffer's PID. * `pager.cacheFile`: the current buffer's cache file. * `pager.cacheId`: the cache ID of said file. Open the `cache:id` URL to view the file. ### gdb gdb should work fine too. You can attach it to buffers by putting a long sleep call in runBuffer, then retrieving the PID as described above. Note that this will upset seccomp, so you should compile with `make TARGET=debug DANGER_DISABLE_SANDBOX=1`. ### Debugging layout bugs One possible workflow: * Save page from your favorite graphical browser. * Binary search the HTML by deleting half of the file at each step. Be careful to not remove any stylesheet LINK or STYLE tags. * Binary search the CSS using the same method. You can format it using the graphical browser's developer tools. The `-o start.console-buffer=false` trick (see above) is especially useful when debugging a flow layout path that the console buffer also needs. Don't forget to add a test case after the fix: ```sh $ cha -C test/layout/config.toml test/layout/my-test-case.html > test/layout/my-test-case.expected ``` Use `config.color.toml` and `my-test-case.color.expected` to preserve colors. ### Sandbox violations You got a syscall number (assuming you're on Linux); look it up in the Linux syscall table for your architecture. To get more context on what happened, you can run `strace -f ./cha -o start.console-buffer [...] 2>a`, trigger the crash, then search for the last occurrence of "--- SIGSYS". Then search backwards on the PID to see the last syscalls. (Incidentally, strace also shows the syscall name, so it may be easier to check like that than looking it up in the syscall table.) ## Resources You may find these links useful. ### WHATWG * HTML: . Includes everything and then some more. * DOM: . Includes events, basic node-related stuff, etc. * Encoding: . The core encoding algorithms are already implemented in Chagashi, so this is now mainly relevant for the TextEncoder JS interface (js/encoding). * URL: . For some incomprehensible reason, it's defined as an equally incomprehensible state machine. types/url implements this. * Fetch: . Networking stuff. Also see for XMLHttpRequest. * Web IDL: . Relevant for Monoucha/JS bindings. Note that these sometimes change daily, especially the HTML standard. ### CSS standards * CSS 2.1: . There's also an "Editor's Draft" 2.2 version: . Not many differences, but usually it's worth to check 2.2 too. Good news is that unlike WHATWG specs, these don't change daily. Bad news is that CSS 2.1 was the last real CSS version, and newer features are spread accross a bunch of random documents with questionable status of stability: . ### Other standards It's unlikely that you will need these, but for completeness' sake: * TOML: . config.toml's base language. * Mailcap: . * Cookies: . * EcmaScript: is the latest draft. ### Nim docs * Manual: . A detailed description of all language features. * Standard library docs: . Everything found in the "std/" namespace. ### MDN MDN is useful if you don't quite understand how a certain feature is supposed to work. It also has links to relevant standards in page footers.