Move render_macro_matcher to own module

Author: dtolnay

src/librustdoc/clean/mod.rs

@@ -5,6 +5,7 @@ mod auto_trait;
 mod blanket_impl;
 crate mod cfg;
 crate mod inline;
+mod render_macro_matchers;
 mod simplify;
 crate mod types;
 crate mod utils;

src/librustdoc/clean/render_macro_matchers.rs

@@ -0,0 +1,191 @@
+use rustc_ast::token::{self, BinOpToken, DelimToken};
+use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_ast_pretty::pprust::state::State as Printer;
+use rustc_ast_pretty::pprust::PrintState;
+use rustc_middle::ty::TyCtxt;
+use rustc_session::parse::ParseSess;
+use rustc_span::source_map::FilePathMapping;
+use rustc_span::symbol::Symbol;
+
+/// Render a macro matcher in a format suitable for displaying to the user
+/// as part of an item declaration.
+pub(super) fn render_macro_matcher(tcx: TyCtxt<'_>, matcher: &TokenTree) -> String {
+    if let Some(snippet) = snippet_equal_to_token(tcx, matcher) {
+        // If the original source code is known, we display the matcher exactly
+        // as present in the source code.
+        return snippet;
+    }
+
+    // If the matcher is macro-generated or some other reason the source code
+    // snippet is not available, we attempt to nicely render the token tree.
+    let mut printer = Printer::new();
+
+    // If the inner ibox fits on one line, we get:
+    //
+    //     macro_rules! macroname {
+    //         (the matcher) => {...};
+    //     }
+    //
+    // If the inner ibox gets wrapped, the cbox will break and get indented:
+    //
+    //     macro_rules! macroname {
+    //         (
+    //             the matcher ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    //             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~!
+    //         ) => {...};
+    //     }
+    printer.cbox(8);
+    printer.word("(");
+    printer.zerobreak();
+    printer.ibox(0);
+    match matcher {
+        TokenTree::Delimited(_span, _delim, tts) => print_tts(&mut printer, tts),
+        // Matcher which is not a Delimited is unexpected and should've failed
+        // to compile, but we render whatever it is wrapped in parens.
+        TokenTree::Token(_) => print_tt(&mut printer, matcher),
+    }
+    printer.end();
+    printer.break_offset_if_not_bol(0, -4);
+    printer.word(")");
+    printer.end();
+    printer.s.eof()
+}
+
+/// Find the source snippet for this token's Span, reparse it, and return the
+/// snippet if the reparsed TokenTree matches the argument TokenTree.
+fn snippet_equal_to_token(tcx: TyCtxt<'_>, matcher: &TokenTree) -> Option<String> {
+    // Find what rustc thinks is the source snippet.
+    // This may not actually be anything meaningful if this matcher was itself
+    // generated by a macro.
+    let source_map = tcx.sess.source_map();
+    let span = matcher.span();
+    let snippet = source_map.span_to_snippet(span).ok()?;
+
+    // Create a Parser.
+    let sess = ParseSess::new(FilePathMapping::empty());
+    let file_name = source_map.span_to_filename(span);
+    let mut parser =
+        match rustc_parse::maybe_new_parser_from_source_str(&sess, file_name, snippet.clone()) {
+            Ok(parser) => parser,
+            Err(diagnostics) => {
+                for mut diagnostic in diagnostics {
+                    diagnostic.cancel();
+                }
+                return None;
+            }
+        };
+
+    // Reparse a single token tree.
+    let mut reparsed_trees = match parser.parse_all_token_trees() {
+        Ok(reparsed_trees) => reparsed_trees,
+        Err(mut diagnostic) => {
+            diagnostic.cancel();
+            return None;
+        }
+    };
+    if reparsed_trees.len() != 1 {
+        return None;
+    }
+    let reparsed_tree = reparsed_trees.pop().unwrap();
+
+    // Compare against the original tree.
+    if reparsed_tree.eq_unspanned(matcher) { Some(snippet) } else { None }
+}
+
+fn print_tt(printer: &mut Printer<'_>, tt: &TokenTree) {
+    match tt {
+        TokenTree::Token(token) => {
+            let token_str = printer.token_to_string(token);
+            printer.word(token_str);
+            if let token::DocComment(..) = token.kind {
+                printer.hardbreak()
+            }
+        }
+        TokenTree::Delimited(_span, delim, tts) => {
+            let open_delim = printer.token_kind_to_string(&token::OpenDelim(*delim));
+            printer.word(open_delim);
+            if !tts.is_empty() {
+                if *delim == DelimToken::Brace {
+                    printer.space();
+                }
+                print_tts(printer, tts);
+                if *delim == DelimToken::Brace {
+                    printer.space();
+                }
+            }
+            let close_delim = printer.token_kind_to_string(&token::CloseDelim(*delim));
+            printer.word(close_delim);
+        }
+    }
+}
+
+fn print_tts(printer: &mut Printer<'_>, tts: &TokenStream) {
+    #[derive(Copy, Clone, PartialEq)]
+    enum State {
+        Start,
+        Dollar,
+        DollarIdent,
+        DollarIdentColon,
+        DollarParen,
+        DollarParenSep,
+        Pound,
+        PoundBang,
+        Ident,
+        Other,
+    }
+
+    use State::*;
+
+    let mut state = Start;
+    for tt in tts.trees() {
+        let (needs_space, next_state) = match &tt {
+            TokenTree::Token(tt) => match (state, &tt.kind) {
+                (Dollar, token::Ident(..)) => (false, DollarIdent),
+                (DollarIdent, token::Colon) => (false, DollarIdentColon),
+                (DollarIdentColon, token::Ident(..)) => (false, Other),
+                (
+                    DollarParen,
+                    token::BinOp(BinOpToken::Plus | BinOpToken::Star) | token::Question,
+                ) => (false, Other),
+                (DollarParen, _) => (false, DollarParenSep),
+                (DollarParenSep, token::BinOp(BinOpToken::Plus | BinOpToken::Star)) => {
+                    (false, Other)
+                }
+                (Pound, token::Not) => (false, PoundBang),
+                (_, token::Ident(symbol, /* is_raw */ false))
+                    if !usually_needs_space_between_keyword_and_open_delim(*symbol) =>
+                {
+                    (true, Ident)
+                }
+                (_, token::Comma | token::Semi) => (false, Other),
+                (_, token::Dollar) => (true, Dollar),
+                (_, token::Pound) => (true, Pound),
+                (_, _) => (true, Other),
+            },
+            TokenTree::Delimited(_, delim, _) => match (state, delim) {
+                (Dollar, DelimToken::Paren) => (false, DollarParen),
+                (Pound | PoundBang, DelimToken::Bracket) => (false, Other),
+                (Ident, DelimToken::Paren | DelimToken::Bracket) => (false, Other),
+                (_, _) => (true, Other),
+            },
+        };
+        if state != Start && needs_space {
+            printer.space();
+        }
+        print_tt(printer, &tt);
+        state = next_state;
+    }
+}
+
+// This rough subset of keywords is listed here to distinguish tokens resembling
+// `f(0)` (no space between ident and paren) from tokens resembling `if let (0,
+// 0) = x` (space between ident and paren).
+fn usually_needs_space_between_keyword_and_open_delim(symbol: Symbol) -> bool {
+    match symbol.as_str() {
+        "as" | "box" | "break" | "const" | "continue" | "crate" | "else" | "enum" | "extern"
+        | "for" | "if" | "impl" | "in" | "let" | "loop" | "macro" | "match" | "mod" | "move"
+        | "mut" | "ref" | "return" | "static" | "struct" | "trait" | "type" | "unsafe" | "use"
+        | "where" | "while" | "yield" => true,
+        _ => false,
+    }
+}