bun.sh/test/js/bun/md/coverage.txt

# Coverage

This file is just a collection of tests designed to activate code in MD4C
which may otherwise be hard to hit. It's to improve our test coverage.


## `md_is_unicode_whitespace__()`

Unicode whitespace (here U+2000) forms a word boundary so these cannot be
resolved as emphasis span because there is no closer mark.

```````````````````````````````` example
*foo *bar
.
<p>*foo *bar</p>
````````````````````````````````


## `md_is_unicode_punct__()`

Ditto for Unicode punctuation (here U+00A1).

```````````````````````````````` example
*foo¡*bar
.
<p>*foo¡*bar</p>
````````````````````````````````


## `md_get_unicode_fold_info()`

```````````````````````````````` example
[Příliš žluťoučký kůň úpěl ďábelské ódy.]

[PŘÍLIŠ ŽLUŤOUČKÝ KŮŇ ÚPĚL ĎÁBELSKÉ ÓDY.]: /url
.
<p><a href="/url">Příliš žluťoučký kůň úpěl ďábelské ódy.</a></p>
````````````````````````````````


## `md_decode_utf8__()` and `md_decode_utf8_before__()`

### Alphanumerical Character (i.e. not whitespace, not punctuation)

Non-whitespace & non-punctuation characters below suppress `_` from being
recognized as an emphasis because `_` should be seen as in-word character:

Example of 1-byte UTF-8 sequence (U+0058):
```````````````````````````````` example
X__foo__X
.
<p>X__foo__X</p>
````````````````````````````````

Example of 2-byte UTF-8 sequence (U+0158):
```````````````````````````````` example
Ř__foo__Ř
.
<p>Ř__foo__Ř</p>
````````````````````````````````

Example of 3-byte UTF-8 sequence (U+0BA3):
```````````````````````````````` example
ண__foo__ண
.
<p>ண__foo__ண</p>
````````````````````````````````

Example of 4-byte UTF-8 sequence (U+13142):
```````````````````````````````` example
𓅂__foo__𓅂
.
<p>𓅂__foo__𓅂</p>
````````````````````````````````

### Whitespace character

Whitespace on the other hand should not suppress `_`:

Example of 1-byte UTF-8 sequence (U+0009):
```````````````````````````````` example
x→__foo__→
.
<p>x <strong>foo</strong></p>
````````````````````````````````
(The initial `x` to suppress indented code block.)

Example of 2-byte UTF-8 sequence (U+00A0):
```````````````````````````````` example
 __foo__
.
<p> <strong>foo</strong> </p>
````````````````````````````````

Example of 3-byte UTF-8 sequence (U+2000):
```````````````````````````````` example
 __foo__
.
<p> <strong>foo</strong> </p>
````````````````````````````````

(AFAIK, there is no 4-byte UTF-8 whitespace.)

### Punctuation character

Punctuation also should not suppress `_`:

Example of 1-byte UTF-8 sequence (U+002E):
```````````````````````````````` example
.__foo__.
.
<p>.<strong>foo</strong>.</p>
````````````````````````````````

Example of 2-byte UTF-8 sequence (U+00B7):
```````````````````````````````` example
·__foo__·
.
<p>·<strong>foo</strong>·</p>
````````````````````````````````

Example of 3-byte UTF-8 sequence (U+0C84):
```````````````````````````````` example
಄__foo__಄
.
<p>಄<strong>foo</strong>಄</p>
````````````````````````````````

Example of 4-byte UTF-8 sequence (U+1039F):
```````````````````````````````` example
𐎟__foo__𐎟
.
<p>𐎟<strong>foo</strong>𐎟</p>
````````````````````````````````


## `md_is_link_destination_A()`

```````````````````````````````` example
[link](</url\.with\.escape>)
.
<p><a href="/url.with.escape">link</a></p>
````````````````````````````````


## `md_link_label_eq()`

```````````````````````````````` example
[foo bar]

[foo bar]: /url
.
<p><a href="/url">foo bar</a></p>
````````````````````````````````


## `md_is_inline_link_spec()`

```````````````````````````````` example
> [link](/url 'foo
> bar')
.
<blockquote>
<p><a href="/url" title="foo
bar">link</a></p>
</blockquote>
````````````````````````````````


## `md_build_ref_def_hashtable()`

All link labels in the following example all have the same FNV1a hash (after
normalization of the label, which means after converting to a vector of Unicode
codepoints and lowercase folding).

So the example triggers quite complex code paths which are not otherwise easily
tested.

```````````````````````````````` example
[foo]: /foo
[qnptgbh]: /qnptgbh
[abgbrwcv]: /abgbrwcv
[abgbrwcv]: /abgbrwcv2
[abgbrwcv]: /abgbrwcv3
[abgbrwcv]: /abgbrwcv4
[alqadfgn]: /alqadfgn

[foo]
[qnptgbh]
[abgbrwcv]
[alqadfgn]
[axgydtdu]
.
<p><a href="/foo">foo</a>
<a href="/qnptgbh">qnptgbh</a>
<a href="/abgbrwcv">abgbrwcv</a>
<a href="/alqadfgn">alqadfgn</a>
[axgydtdu]</p>
````````````````````````````````

For the sake of completeness, the following C program was used to find the hash
collisions by brute force:

~~~

#include <stdio.h>
#include <string.h>


static unsigned etalon;



#define MD_FNV1A_BASE       2166136261
#define MD_FNV1A_PRIME      16777619

static inline unsigned
fnv1a(unsigned base, const void* data, size_t n)
{
    const unsigned char* buf = (const unsigned char*) data;
    unsigned hash = base;
    size_t i;

    for(i = 0; i < n; i++) {
        hash ^= buf[i];
        hash *= MD_FNV1A_PRIME;
    }

    return hash;
}


static unsigned
unicode_hash(const char* data, size_t n)
{
    unsigned value;
    unsigned hash = MD_FNV1A_BASE;
    int i;

    for(i = 0; i < n; i++) {
        value = data[i];
        hash = fnv1a(hash, &value, sizeof(unsigned));
    }

    return hash;
}


static void
recurse(char* buffer, size_t off, size_t len)
{
    int ch;

    if(off < len - 1) {
        for(ch = 'a'; ch <= 'z'; ch++) {
            buffer[off] = ch;
            recurse(buffer, off+1, len);
        }
    } else {
        for(ch = 'a'; ch <= 'z'; ch++) {
            buffer[off] = ch;
            if(unicode_hash(buffer, len) == etalon) {
                printf("Dup: %.*s\n", (int)len, buffer);
            }
        }
    }
}

int
main(int argc, char** argv)
{
    char buffer[32];
    int len;

    if(argc < 2)
        etalon = unicode_hash("foo", 3);
    else
        etalon = unicode_hash(argv[1], strlen(argv[1]));

    for(len = 1; len <= sizeof(buffer); len++)
        recurse(buffer, 0, len);

    return 0;
}
~~~


## Flag `MD_FLAG_COLLAPSEWHITESPACE`

```````````````````````````````` example
foo  bar → baz
.
<p>foo bar baz</p>
.
--fcollapse-whitespace
````````````````````````````````