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Fix bugs in JS and CSS minifiers
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- Fix JS minifier bug: We need to keep a semicolon after
  `}` that ends function bodies.

- Added the removal of round brackets in `(single_argument)=>{...}`.

- Fix the line and column calculation in the CSS minifier.

- Fix CSS minifier bug: Do not expect `=` before quote in DOCTYPE tag.
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Lerchensporn committed May 14, 2023
1 parent d16a9a8 commit 9bab818
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Showing 5 changed files with 177 additions and 40 deletions.
2 changes: 1 addition & 1 deletion Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ release: $(build_dir)/minify

$(build_dir)/minify: minify.c
mkdir -p $(build_dir)
cc -O3 -o $(build_dir)/minify minify.c
cc -Os -o $(build_dir)/minify minify.c
strip $(build_dir)/minify

.PHONY: debug
Expand Down
7 changes: 7 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,13 @@ Some alternative minifiers choose different objectives.
that is good to be alerted about. Strict parsing is a good practice to
promote standard conformity.

## Alternative multi-format minifier

https://github.com/tdewolff/minify

Written in Go. Minifies HTML, XML, SVG, JS, CSS, JSON. It is in the package
repository of Alpine Linux and statically linked binary releases exist.

## Alternative CSS minifiers

https://github.com/csstidy-c/csstidy
Expand Down
194 changes: 156 additions & 38 deletions minify.c
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Original file line number Diff line number Diff line change
Expand Up @@ -118,8 +118,6 @@ static bool is_nestable_atrule(const char *atrule, unsigned int atrule_length)

char *minify_css(const char *css)
{
// Returns the minified CSS, which has to be freed, or NULL in case of error.

enum {
SYNTAX_BLOCK_STYLE,
SYNTAX_BLOCK_RULE_START,
Expand Down Expand Up @@ -515,67 +513,161 @@ char *minify_js(const char *js)
const char *trim_around_chars = "%<>+*/-=,(){}[]!~;|&^:?";
const char *identifier_delimiters = "()[]{}; \t\r\n:=><+-*/~";

// Array index is the nesting level, value says whether the “{...}” block is preceded by “=>”.

bool curly_block_is_arrow_function[256];
enum {
CURLY_BLOCK_UNKNOWN,
CURLY_BLOCK_FUNCBODY,
} curly_block[256];
int curly_nesting_level = 0;

enum {
ROUND_BLOCK_UNKNOWN,
ROUND_BLOCK_FUNCDEF_PARAMS,
} round_block[256];
int round_nesting_level = 0;

while (true) {
if (js[i] == '\0') {
js_min[js_min_length++] = '\0';
break;
}
if (js[i] == '=' && js[i + 1] == '>') {
js_min[js_min_length++] = '=';
js_min[js_min_length++] = '>';
i += 2;
if (
! strncmp(&js[i], "function", sizeof "function" - 1) &&
strchr(identifier_delimiters, js[i + sizeof "function" - 1]) != NULL
) {
// Regular functions cannot be safely replaced by arrow functions. Arrow functions
// cannot be used as constructors: `new arrow_function()` where `arrow_function` is an
// arrow function is invalid.

// Here we consume the input until ( of the parameter list.

strcpy(&js_min[js_min_length], "function");
js_min_length += sizeof "function" - 1;

i += sizeof "function" - 1;
i = js_skip_whitespaces_comments(js, i, &line, &last_newline);
if (js[i] == '{') {
curly_block_is_arrow_function[curly_nesting_level] = true;
js_min[js_min_length++] = '{';
curly_nesting_level += 1;
i += 1;
if (js[i] != '(') {
js_min[js_min_length++] = ' ';
while (strchr(identifier_delimiters, js[i]) == NULL) {
js_min[js_min_length++] = js[i++];
}
}
else {
curly_block_is_arrow_function[curly_nesting_level] = false;
i = js_skip_whitespaces_comments(js, i, &line, &last_newline);
if (js[i] != '(') {
fprintf(stderr, "Expected ( in line %d, column %d\n", line, i - last_newline);
free(js_min);
return NULL;
}
if (++round_nesting_level == sizeof round_block / sizeof round_block[0]) {
free(js_min);
fprintf(stderr, "The nesting level of round brackets is too deep");
return NULL;
}
round_block[round_nesting_level] = ROUND_BLOCK_FUNCDEF_PARAMS;
js_min[js_min_length++] = '(';
i += 1;
continue;
}
if (js[i] == '{') {
curly_nesting_level += 1;
if (curly_nesting_level == sizeof curly_block_is_arrow_function / sizeof (bool)) {
if (++curly_nesting_level == sizeof curly_block / sizeof curly_block[0]) {
free(js_min);
fprintf(stderr, "The nesting level of curly brackets is too deep");
return NULL;
}
if (
js_min_length > 2 && (
js_min[js_min_length - 2] == '=' && js_min[js_min_length - 1] == '>' ||
js_min[js_min_length - 1] == ')' &&
round_block[round_nesting_level + 1] == ROUND_BLOCK_FUNCDEF_PARAMS
)
) {
curly_block[curly_nesting_level] = CURLY_BLOCK_FUNCBODY;
}
else {
curly_block[curly_nesting_level] = CURLY_BLOCK_UNKNOWN;
}
js_min[js_min_length++] = '{';
i += 1;
continue;
}
if (js[i] == '(') {
if (++round_nesting_level == sizeof round_block / sizeof round_block[0]) {
free(js_min);
fprintf(stderr, "The nesting level of round brackets is too deep");
return NULL;
}

i += 1;

// Removing round brackets around single parameters with no default
// value of arrow functions.

bool remove_round_brackets_around_param = false;

int k = i;
k = js_skip_whitespaces_comments(js, k, &line, &last_newline);
int arg_start = k;
do {
k += 1;
} while (strchr(",)= \n\r\t/*", js[k]) == NULL);
int arg_end = k;
k = js_skip_whitespaces_comments(js, k, &line, &last_newline);
if (js[k] == ')') {
k = js_skip_whitespaces_comments(js, k + 1, &line, &last_newline);
if (js[k] == '=' && js[k + 1] == '>') {
remove_round_brackets_around_param = true;
}
}

if (remove_round_brackets_around_param) {
strncpy(&js_min[js_min_length], &js[arg_start], arg_end - arg_start);
js_min_length += arg_end - arg_start;
i = k;
}
else {
round_block[round_nesting_level] = ROUND_BLOCK_UNKNOWN;
js_min[js_min_length++] = '(';
}
continue;
}
if (js[i] == '}') {
curly_nesting_level -= 1;
if (--curly_nesting_level < 0) {
free(js_min);
fprintf(stderr, "Unexpected } in line %d, column %d\n", line, i - last_newline);
return NULL;
}
js_min[js_min_length++] = '}';
i += 1;
continue;
}
if (js[i] == ')') {
if (--round_nesting_level < 0) {
free(js_min);
fprintf(stderr, "Unexpected ) in line %d, column %d\n", line, i - last_newline);
return NULL;
}
js_min[js_min_length++] = ')';
i += 1;
continue;
}
if (js[i] == ';') {
char before_semicolon = (i == 0 ? '}' : js[i - 1]);
char before_semicolon = (js_min_length == 0 ? '}' : js_min[js_min_length - 1]);
do {
i = js_skip_whitespaces_comments(js, i + 1, &line, &last_newline);
} while (js[i] == ';');

// ; can be removed after `}`, except if it is an arrow function
// block, i.e. if the matching `{` is preceded by `=>`. Semicolon
// cannot be removed in `a=()=>{};b=0`.
// `;` can be removed after `}`, except if it ends a function body.
// Semicolon cannot be removed in `a=()=>{};b=0`.

if ((before_semicolon != '}' || curly_block_is_arrow_function[curly_nesting_level]) &&
js[i] != '}' && js[i] != '\0')
{
if (
(before_semicolon != '}' ||
curly_block[curly_nesting_level + 1] == CURLY_BLOCK_FUNCBODY) &&
js[i] != '}' && js[i] != '\0'
) {
js_min[js_min_length++] = ';';
}
continue;
}
if (js[i] == '/' && js[i + 1] != '/' &&
if (js[i] == '/' && js[i + 1] != '/' && js[i + 1] != '*' &&
(js_min_length == 0 || strchr("^!&|([><+-*i%", js_min[js_min_length - 1]) != NULL))
{
// This is a regex object.
Expand Down Expand Up @@ -629,12 +721,18 @@ char *minify_js(const char *js)
js[i] == '/' && js[i + 1] == '*' ||
js[i] == '/' && js[i + 1] == '/')
{
if (i == 0 || strchr(trim_around_chars, js[i - 1]) != NULL) {
i = js_skip_whitespaces_comments(js, i, &line, &last_newline);
continue;
}
int old_line = line;
i = js_skip_whitespaces_comments(js, i, &line, &last_newline);
if (old_line != line && js_min[js_min_length - 1] == '}' &&
curly_block[curly_nesting_level + 1] == CURLY_BLOCK_FUNCBODY &&
js[i] != '\0' && js[i] != '}')
{
js_min[js_min_length++] = ';';
continue;
}
if (i == 0 || strchr(trim_around_chars, js_min[js_min_length - 1]) != NULL) {
continue;
}
if (strchr(trim_around_chars, js[i]) == NULL) {
js_min[js_min_length++] = (old_line != line ? '\n' : ' ');
}
Expand Down Expand Up @@ -681,7 +779,8 @@ static char *minify_sgml(const char *sgml, enum sgml_subset sgml_subset)

enum {
SYNTAX_BLOCK_TAG,
SYNTAX_BLOCK_CONTENT
SYNTAX_BLOCK_CONTENT,
SYNTAX_BLOCK_DOCTYPE,
} syntax_block = SYNTAX_BLOCK_CONTENT;

const char *current_tag;
Expand All @@ -703,6 +802,10 @@ static char *minify_sgml(const char *sgml, enum sgml_subset sgml_subset)
if (! strncmp(&sgml[i], "<!--", 4)) {
i += 4;
while (sgml[i] != '\0' && strncmp(&sgml[i], "-->", 3)) {
if (sgml[i] == '\n') {
line += 1;
last_newline = i;
}
i += 1;
}
if (sgml[i] == '\0') {
Expand Down Expand Up @@ -746,6 +849,12 @@ static char *minify_sgml(const char *sgml, enum sgml_subset sgml_subset)
whitespace_before_tag =
sgml_min_length > 0 && is_whitespace(sgml_min[sgml_min_length - 1]);
i += 1;
if (! strnicmp(&sgml[i], "!DOCTYPE", sizeof "!DOCTYPE" - 1)) {
syntax_block = SYNTAX_BLOCK_DOCTYPE;
sgml_min[sgml_min_length++] = '<';
continue;
}

is_closing_tag = (sgml[i] == '/');
current_tag = &sgml[i];
current_tag_length = 0;
Expand All @@ -756,7 +865,7 @@ static char *minify_sgml(const char *sgml, enum sgml_subset sgml_subset)
current_tag_length += 1;
}
syntax_block = SYNTAX_BLOCK_TAG;
sgml_min[sgml_min_length++] = sgml[i - 1];
sgml_min[sgml_min_length++] = '<';
continue;
}
if (sgml[i] == '>') {
Expand All @@ -773,6 +882,7 @@ static char *minify_sgml(const char *sgml, enum sgml_subset sgml_subset)
// Transform `<sgml></sgml>` to `<sgml/>`. This would be illegal for HTML.

else if (sgml_subset == SGML_SUBSET_XML &&
syntax_block != SYNTAX_BLOCK_DOCTYPE &&
sgml[i + 1] == '<' && sgml[i + 2] == '/' &&
! strncmp(current_tag, &sgml[i + 3], current_tag_length) &&
(is_whitespace(sgml[i + 3 + current_tag_length]) ||
Expand All @@ -796,14 +906,18 @@ static char *minify_sgml(const char *sgml, enum sgml_subset sgml_subset)
// Ignore whitespace except between opening and closing tags

int k = i;
int k_line = line;
int k_last_newline = last_newline;
while (is_whitespace(sgml[k])) {
if (sgml[i] == '\n') {
line += 1;
last_newline = i;
if (sgml[k] == '\n') {
k_line += 1;
k_last_newline = k;
}
k += 1;
}
if (sgml[k] == '<' && (is_closing_tag || sgml[k + 1] != '/')) {
line = k_line;
last_newline = k_last_newline;
i = k;
}
}
Expand All @@ -826,7 +940,9 @@ static char *minify_sgml(const char *sgml, enum sgml_subset sgml_subset)
continue;
}
if (sgml[i] == '"' || sgml[i] == '\'') {
if (sgml_min_length == 0 || sgml_min[sgml_min_length - 1] != '=') {
if (syntax_block != SYNTAX_BLOCK_DOCTYPE &&
(sgml_min_length == 0 || sgml_min[sgml_min_length - 1] != '='))
{
free(sgml_min);
fprintf(stderr, "Expected = before quote in line %d, column %d\n",
line, i - last_newline);
Expand All @@ -835,7 +951,7 @@ static char *minify_sgml(const char *sgml, enum sgml_subset sgml_subset)
char quote = sgml[i];
i += 1;
bool need_quotes;
if (sgml_subset == SGML_SUBSET_XML) {
if (sgml_subset == SGML_SUBSET_XML || syntax_block == SYNTAX_BLOCK_DOCTYPE) {
need_quotes = true;
}
else {
Expand Down Expand Up @@ -1038,6 +1154,8 @@ int main(int argc, char *argv[])
case FORMAT_HTML:
input_min = minify_html(input);
break;
default:
input_min = NULL;
}
if (input_min == NULL) {
return EXIT_FAILURE;
Expand Down
12 changes: 12 additions & 0 deletions test-js.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,14 @@ expected='a=0
b=0'
assert "$expected" "$input"

input='{function(){};};a=3'
expected='{function(){}}a=3'
assert "$expected" "$input"

input='( abc ) => 1;'
expected='abc=>1'
assert "$expected" "$input"

input='a=()=>{true};a=3'
expected='a=()=>{!0};a=3'
assert "$expected" "$input"
Expand All @@ -29,4 +37,8 @@ input='/ /; 3 > / /;a & / /'
expected='/ /;3>/ /;a&/ /'
assert "$expected" "$input"

input='function () {}; function () {}\n if(true) {} ; a=3'
expected='function(){};function(){};if(!0){}a=3'
assert "$expected" "$input"

echo 'Passed all tests'
2 changes: 1 addition & 1 deletion test-random-input.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -13,4 +13,4 @@ for format in css js xml html; do
done
done

echo Passed the test - no crash ocurred
echo Passed the test - no crash occurred

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