zulip/tools/lib/template_parser.py

from typing import Callable, List, Optional


class FormattedException(Exception):
    pass


class TemplateParserException(Exception):
    def __init__(self, message: str) -> None:
        self.message = message

    def __str__(self) -> str:
        return self.message


class TokenizationException(Exception):
    def __init__(self, message: str, line_content: Optional[str] = None) -> None:
        self.message = message
        self.line_content = line_content


class TokenizerState:
    def __init__(self) -> None:
        self.i = 0
        self.line = 1
        self.col = 1


class Token:
    def __init__(self, kind: str, s: str, tag: str, line: int, col: int, line_span: int) -> None:
        self.kind = kind
        self.s = s
        self.tag = tag
        self.line = line
        self.col = col
        self.line_span = line_span

        # These get set during the validation pass.
        self.start_token: Optional[Token] = None
        self.end_token: Optional[Token] = None


def tokenize(text: str) -> List[Token]:
    def advance(n: int) -> None:
        for _ in range(n):
            state.i += 1
            if state.i >= 0 and text[state.i - 1] == "\n":
                state.line += 1
                state.col = 1
            else:
                state.col += 1

    def looking_at(s: str) -> bool:
        return text[state.i : state.i + len(s)] == s

    def looking_at_htmlcomment() -> bool:
        return looking_at("<!--")

    def looking_at_handlebarcomment() -> bool:
        return looking_at("{{!")

    def looking_at_djangocomment() -> bool:
        return looking_at("{#")

    def looking_at_handlebarpartial() -> bool:
        return looking_at("{{>")

    def looking_at_html_start() -> bool:
        return looking_at("<") and not looking_at("</")

    def looking_at_html_end() -> bool:
        return looking_at("</")

    def looking_at_handlebars_start() -> bool:
        return looking_at("{{#") or looking_at("{{^") or looking_at("{{~#")

    def looking_at_handlebars_else() -> bool:
        return looking_at("{{else")

    def looking_at_template_var() -> bool:
        return looking_at("{")

    def looking_at_handlebars_end() -> bool:
        return looking_at("{{/") or looking_at("{{~/")

    def looking_at_django_start() -> bool:
        return looking_at("{% ")

    def looking_at_django_else() -> bool:
        return looking_at("{% else") or looking_at("{% elif")

    def looking_at_django_end() -> bool:
        return looking_at("{% end")

    def looking_at_jinja2_end_whitespace_stripped() -> bool:
        return looking_at("{%- end")

    def looking_at_jinja2_start_whitespace_stripped_type2() -> bool:
        # This function detects tag like {%- if foo -%}...{% endif %}
        return looking_at("{%-") and not looking_at("{%- end")

    def looking_at_whitespace() -> bool:
        return looking_at("\n") or looking_at(" ")

    state = TokenizerState()
    tokens: List[Token] = []

    while state.i < len(text):
        try:
            if looking_at_htmlcomment():
                s = get_html_comment(text, state.i)
                tag = s[4:-3]
                kind = "html_comment"
            elif looking_at_handlebarcomment():
                s = get_handlebar_comment(text, state.i)
                tag = s[3:-2]
                kind = "handlebar_comment"
            elif looking_at_djangocomment():
                s = get_django_comment(text, state.i)
                tag = s[2:-2]
                kind = "django_comment"
            elif looking_at_handlebarpartial():
                s = get_handlebar_partial(text, state.i)
                tag = s[9:-2]
                kind = "handlebars_singleton"
            elif looking_at_html_start():
                s = get_html_tag(text, state.i)
                if s.endswith("/>"):
                    end_offset = -2
                else:
                    end_offset = -1
                tag_parts = s[1:end_offset].split()

                if not tag_parts:
                    raise TemplateParserException("Tag name missing")

                tag = tag_parts[0]

                if tag == "!DOCTYPE":
                    kind = "html_doctype"
                elif s.endswith("/>"):
                    kind = "html_singleton"
                else:
                    kind = "html_start"
            elif looking_at_html_end():
                s = get_html_tag(text, state.i)
                tag = s[2:-1]
                kind = "html_end"
            elif looking_at_handlebars_else():
                s = get_handlebars_tag(text, state.i)
                tag = "else"
                kind = "handlebars_else"
            elif looking_at_handlebars_start():
                s = get_handlebars_tag(text, state.i)
                tag = s[3:-2].split()[0].strip("#")
                if tag.startswith("*"):
                    tag = tag[1:]
                kind = "handlebars_start"
            elif looking_at_handlebars_end():
                s = get_handlebars_tag(text, state.i)
                tag = s[3:-2].strip("/#~")
                kind = "handlebars_end"
            elif looking_at_django_else():
                s = get_django_tag(text, state.i)
                tag = "else"
                kind = "django_else"
            elif looking_at_django_end():
                s = get_django_tag(text, state.i)
                tag = s[6:-3]
                kind = "django_end"
            elif looking_at_django_start():
                # must check this after end/else
                s = get_django_tag(text, state.i)
                tag = s[3:-2].split()[0]
                kind = "django_start"

                if s[-3] == "-":
                    kind = "jinja2_whitespace_stripped_start"
            elif looking_at_jinja2_end_whitespace_stripped():
                s = get_django_tag(text, state.i)
                tag = s[7:-3]
                kind = "jinja2_whitespace_stripped_end"
            elif looking_at_jinja2_start_whitespace_stripped_type2():
                s = get_django_tag(text, state.i, stripped=True)
                tag = s[3:-3].split()[0]
                kind = "jinja2_whitespace_stripped_type2_start"
            elif looking_at_template_var():
                # order is important here
                s = get_template_var(text, state.i)
                tag = "var"
                kind = "template_var"
            elif looking_at("\n"):
                s = "\n"
                tag = "newline"
                kind = "newline"
            elif looking_at(" "):
                s = get_spaces(text, state.i)
                tag = ""
                if not tokens or tokens[-1].kind == "newline":
                    kind = "indent"
                else:
                    kind = "whitespace"
            elif text[state.i] in "{<":
                snippet = text[state.i :][:15]
                raise AssertionError(f"tool cannot parse {snippet}")
            else:
                s = get_text(text, state.i)
                if s == "":
                    continue
                tag = ""
                kind = "text"
        except TokenizationException as e:
            raise FormattedException(
                f'''{e.message} at line {state.line} col {state.col}:"{e.line_content}"''',
            )

        line_span = len(s.strip("\n").split("\n"))
        token = Token(
            kind=kind,
            s=s,
            tag=tag.strip(),
            line=state.line,
            col=state.col,
            line_span=line_span,
        )
        tokens.append(token)
        advance(len(s))

    return tokens


HTML_VOID_TAGS = {
    "area",
    "base",
    "br",
    "col",
    "command",
    "embed",
    "hr",
    "img",
    "input",
    "keygen",
    "link",
    "meta",
    "param",
    "source",
    "track",
    "wbr",
}

# The following excludes some obscure tags that are never used
# in Zulip code.
HTML_INLINE_TAGS = {
    "a",
    "b",
    "br",
    "button",
    "cite",
    "code",
    "em",
    "i",
    "img",
    "input",
    "kbd",
    "label",
    "object",
    "script",
    "select",
    "small",
    "span",
    "strong",
    "textarea",
}


def tag_flavor(token: Token) -> Optional[str]:
    kind = token.kind
    tag = token.tag
    if kind in (
        "django_comment",
        "handlebar_comment",
        "handlebars_singleton",
        "html_comment",
        "html_doctype",
        "html_singleton",
        "indent",
        "newline",
        "template_var",
        "text",
        "whitespace",
    ):
        return None

    if kind in ("handlebars_start", "html_start"):
        return "start"
    elif kind in (
        "django_else",
        "django_end",
        "handlebars_else",
        "handlebars_end",
        "html_end",
        "jinja2_whitespace_stripped_end",
    ):
        return "end"
    elif kind in {
        "django_start",
        "django_else",
        "jinja2_whitespace_stripped_start",
        "jinja2_whitespace_stripped_type2_start",
    }:
        if is_django_block_tag(tag):
            return "start"
        else:
            return None
    else:
        raise AssertionError(f"tools programmer neglected to handle {kind} tokens")


def validate(fn: Optional[str] = None, text: Optional[str] = None) -> List[Token]:
    assert fn or text

    if fn is None:
        fn = "<in memory file>"

    if text is None:
        with open(fn) as f:
            text = f.read()

    lines = text.split("\n")

    try:
        tokens = tokenize(text)
    except FormattedException as e:
        raise TemplateParserException(
            f"""
            fn: {fn}
            {e}"""
        )

    prevent_whitespace_violations(fn, tokens)

    class State:
        def __init__(self, func: Callable[[Token], None]) -> None:
            self.depth = 0
            self.foreign = False
            self.matcher = func

    def no_start_tag(token: Token) -> None:
        raise TemplateParserException(
            f"""
            No start tag
            fn: {fn}
            end tag:
                {token.tag}
                line {token.line}, col {token.col}
            """
        )

    state = State(no_start_tag)

    def start_tag_matcher(start_token: Token) -> None:
        state.depth += 1
        start_tag = start_token.tag.strip("~")
        start_line = start_token.line
        start_col = start_token.col

        old_matcher = state.matcher
        old_foreign = state.foreign

        if start_tag in ["math", "svg"]:
            state.foreign = True

        def f(end_token: Token) -> None:
            is_else_tag = end_token.tag == "else"

            end_tag = end_token.tag.strip("~")
            end_line = end_token.line
            end_col = end_token.col

            def report_problem() -> Optional[str]:
                if (start_tag == "code") and (end_line == start_line + 1):
                    return "Code tag is split across two lines."

                if is_else_tag:
                    # We are not completely rigorous about having a sensible
                    # order of if/elif/elif/else, but we catch obviously
                    # mismatching else tags.
                    if start_tag not in ("if", "else", "unless"):
                        return f"Unexpected else/elif tag encountered after {start_tag} tag."
                elif start_tag != end_tag:
                    return f"Mismatched tags: ({start_tag} != {end_tag})"

                return None

            problem = report_problem()
            if problem:
                raise TemplateParserException(
                    f"""
                    fn: {fn}
                   {problem}
                    start:
                        {start_token.s}
                        line {start_line}, col {start_col}
                    end tag:
                        {end_tag}
                        line {end_line}, col {end_col}
                    """
                )

            if not is_else_tag:
                state.matcher = old_matcher
                state.foreign = old_foreign
                state.depth -= 1

            # TODO: refine this for the else/elif use cases
            end_token.start_token = start_token
            start_token.end_token = end_token

        state.matcher = f

    for token in tokens:
        kind = token.kind
        tag = token.tag

        if not state.foreign:
            if kind == "html_start":
                if tag in HTML_VOID_TAGS:
                    raise TemplateParserException(
                        f"Tag must be self-closing: {tag} at {fn} line {token.line}, col {token.col}"
                    )
            elif kind == "html_singleton":
                if not state.foreign and tag not in HTML_VOID_TAGS:
                    raise TemplateParserException(
                        f"Tag must not be self-closing: {tag} at {fn} line {token.line}, col {token.col}"
                    )

        flavor = tag_flavor(token)
        if flavor == "start":
            start_tag_matcher(token)
        elif flavor == "end":
            state.matcher(token)

    if state.depth != 0:
        raise TemplateParserException("Missing end tag")

    ensure_matching_indentation(fn, tokens, lines)

    return tokens


def ensure_matching_indentation(fn: str, tokens: List[Token], lines: List[str]) -> None:
    for token in tokens:
        if token.start_token is None:
            continue

        end_token = token

        start_token = token.start_token
        start_line = start_token.line
        start_col = start_token.col
        start_tag = start_token.tag
        end_tag = end_token.tag.strip("~")
        end_line = end_token.line
        end_col = end_token.col

        def has_bad_indentation() -> bool:
            is_inline_tag = start_tag in HTML_INLINE_TAGS and start_token.kind == "html_start"

            if end_line > start_line + 1:
                if is_inline_tag:
                    end_row_text = lines[end_line - 1]
                    if end_row_text.lstrip().startswith(end_token.s):
                        if end_col != start_col:
                            return True
                else:
                    if end_col != start_col:
                        return True

            return False

        if has_bad_indentation():
            raise TemplateParserException(
                f"""
                fn: {fn}
                Indentation for start/end tags does not match.
                start tag: {start_token.s}

                start:
                    line {start_line}, col {start_col}
                end:
                    {end_tag}
                    line {end_line}, col {end_col}
                """
            )


def prevent_extra_newlines(fn: str, tokens: List[Token]) -> None:
    count = 0

    for token in tokens:
        if token.kind != "newline":
            count = 0
            continue

        count += 1
        if count >= 4:
            raise TemplateParserException(
                f"""Please avoid so many blank lines near row {token.line} in {fn}."""
            )


def prevent_whitespace_violations(fn: str, tokens: List[Token]) -> None:
    if tokens[0].kind in ("indent", "whitespace"):
        raise TemplateParserException(f" Please remove the whitespace at the beginning of {fn}.")

    prevent_extra_newlines(fn, tokens)

    for i in range(1, len(tokens) - 1):
        token = tokens[i]
        next_token = tokens[i + 1]

        if token.kind == "indent":
            if next_token.kind in ("indent", "whitespace"):
                raise AssertionError("programming error parsing indents")

            if next_token.kind == "newline":
                raise TemplateParserException(
                    f"""Please just make row {token.line} in {fn} a truly blank line (no spaces)."""
                )

            if len(token.s) % 4 != 0:
                raise TemplateParserException(
                    f"""
                        Please use 4-space indents for template files. Most of our
                        codebase (including Python and JavaScript) uses 4-space indents,
                        so it's worth investing in configuring your editor to use
                        4-space indents for files like
                        {fn}

                        The line at row {token.line} is indented with {len(token.s)} spaces.
                    """
                )

        if token.kind == "whitespace":
            if len(token.s) > 1:
                raise TemplateParserException(
                    f"""
                        We did not expect this much whitespace at row {token.line} column {token.col} in {fn}.
                    """
                )
            if next_token.kind == "newline":
                raise TemplateParserException(
                    f"""
                        Unexpected trailing whitespace at row {token.line} column {token.col} in {fn}.
                    """
                )


def is_django_block_tag(tag: str) -> bool:
    return tag in [
        "autoescape",
        "block",
        "comment",
        "for",
        "if",
        "ifequal",
        "macro",
        "verbatim",
        "blocktrans",
        "trans",
        "raw",
        "with",
    ]


def get_handlebars_tag(text: str, i: int) -> str:
    end = i + 2
    while end < len(text) - 1 and text[end] != "}":
        end += 1
    if text[end] != "}" or text[end + 1] != "}":
        raise TokenizationException('Tag missing "}}"', text[i : end + 2])
    s = text[i : end + 2]
    return s


def get_spaces(text: str, i: int) -> str:
    s = ""
    while i < len(text) and text[i] in " ":
        s += text[i]
        i += 1
    return s


def get_text(text: str, i: int) -> str:
    s = ""
    while i < len(text) and text[i] not in "{<":
        s += text[i]
        i += 1
    return s.strip()


def get_django_tag(text: str, i: int, stripped: bool = False) -> str:
    end = i + 2
    if stripped:
        end += 1
    while end < len(text) - 1 and text[end] != "%":
        end += 1
    if text[end] != "%" or text[end + 1] != "}":
        raise TokenizationException('Tag missing "%}"', text[i : end + 2])
    s = text[i : end + 2]
    return s


def get_html_tag(text: str, i: int) -> str:
    quote_count = 0
    end = i + 1
    unclosed_end = 0
    while end < len(text) and (text[end] != ">" or quote_count % 2 != 0 and text[end] != "<"):
        if text[end] == '"':
            quote_count += 1
        if not unclosed_end and text[end] == "<":
            unclosed_end = end
        end += 1
    if quote_count % 2 != 0:
        if unclosed_end:
            raise TokenizationException("Unbalanced quotes", text[i:unclosed_end])
        else:
            raise TokenizationException("Unbalanced quotes", text[i : end + 1])
    if end == len(text) or text[end] != ">":
        raise TokenizationException('Tag missing ">"', text[i : end + 1])
    s = text[i : end + 1]
    return s


def get_html_comment(text: str, i: int) -> str:
    end = i + 7
    unclosed_end = 0
    while end <= len(text):
        if text[end - 3 : end] == "-->":
            return text[i:end]
        if not unclosed_end and text[end] == "<":
            unclosed_end = end
        end += 1
    raise TokenizationException("Unclosed comment", text[i:unclosed_end])


def get_handlebar_comment(text: str, i: int) -> str:
    end = i + 5
    unclosed_end = 0
    while end <= len(text):
        if text[end - 2 : end] == "}}":
            return text[i:end]
        if not unclosed_end and text[end] == "<":
            unclosed_end = end
        end += 1
    raise TokenizationException("Unclosed comment", text[i:unclosed_end])


def get_template_var(text: str, i: int) -> str:
    end = i + 3
    unclosed_end = 0
    while end <= len(text):
        if text[end - 1] == "}":
            if end < len(text) and text[end] == "}":
                end += 1
            return text[i:end]
        if not unclosed_end and text[end] == "<":
            unclosed_end = end
        end += 1
    raise TokenizationException("Unclosed var", text[i:unclosed_end])


def get_django_comment(text: str, i: int) -> str:
    end = i + 4
    unclosed_end = 0
    while end <= len(text):
        if text[end - 2 : end] == "#}":
            return text[i:end]
        if not unclosed_end and text[end] == "<":
            unclosed_end = end
        end += 1
    raise TokenizationException("Unclosed comment", text[i:unclosed_end])


def get_handlebar_partial(text: str, i: int) -> str:
    end = i + 10
    unclosed_end = 0
    while end <= len(text):
        if text[end - 2 : end] == "}}":
            return text[i:end]
        if not unclosed_end and text[end] == "<":
            unclosed_end = end
        end += 1
    raise TokenizationException("Unclosed partial", text[i:unclosed_end])