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92 lines
2.8 KiB
Plaintext
92 lines
2.8 KiB
Plaintext
= Design Notes
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== Problems:
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Translating C to Go is harder than it looks.
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Jan says: It's impossible in the general case to turn C char* into Go
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[]byte. It's possible to do it probably often for concrete C code
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cases - based also on author's C coding style. The first problem this
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runs into is that Go does not guarantee that the backing array will
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keep its address stable due to Go movable stacks. C expects the
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opposite, a pointer never magically modifies itself, so some code will
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fail.
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INSERT CODE EXAMPLES ILLUSTRATING THE PROBLEM HERE
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== How the parser works
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There are no comment nodes in the C AST. Instead every cc.Token has a
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Sep field: https://godoc.org/modernc.org/cc/v3#Token
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It captures, when configured to do so, all white space preceding the
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token, combined, including comments, if any. So we have all white
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space/comments information for every token in the AST. A final white
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space/comment, preceding EOF, is available as field TrailingSeperator
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in the AST: https://godoc.org/modernc.org/cc/v3#AST.
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To get the lexically first white space/comment for any node, use
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tokenSeparator():
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https://gitlab.com/cznic/ccgo/-/blob/6551e2544a758fdc265c8fac71fb2587fb3e1042/v3/go.go#L1476
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The same with a default value is comment():
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https://gitlab.com/cznic/ccgo/-/blob/6551e2544a758fdc265c8fac71fb2587fb3e1042/v3/go.go#L1467
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== Looking forward
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Eric says: In my visualization of how the translator would work, the
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output of a ccgo translation of a module at any given time is a file
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of pseudo-Go code in which some sections may be enclosed by a Unicode
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bracketing character (presently using the guillemot quotes U+ab and
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U+bb) meaning "this is not Go yet" that intentionally makes the Go
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compiler barf. This expresses a color on the AST nodes.
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So, for example, if I'm translating hello.c with a ruleset that does not
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include print -> fmt.Printf, this:
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---------------------------------------------------------
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#include <stdio>
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/* an example comment */
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int main(int argc, char *argv[])
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{
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printf("Hello, World")
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}
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---------------------------------------------------------
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becomes this without any explicit rules at all:
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---------------------------------------------------------
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«#include <stdio>»
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/* an example comment */
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func main
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{
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«printf(»"Hello, World"!\n"«)»
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}
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---------------------------------------------------------
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Then, when the rule print -> fmt.Printf is added, it becomes
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---------------------------------------------------------
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import (
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"fmt"
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)
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/* an example comment */
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func main
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{
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fmt.Printf("Hello, World"!\n")
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}
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---------------------------------------------------------
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because with that rule the AST node corresponding to the printf
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call can be translated and colored "Go". This implies an import
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of fmt. We observe that there are no longer C-colored spans
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and drop the #includes.
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// end
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