Merge pull request #55 from eddyb/const-values

v0: demangle structural constants and &str.

Author: alexcrichton

src/v0.rs

@@ -1,5 +1,5 @@
 use core::convert::TryFrom;
-use core::{char, fmt, iter, mem};
+use core::{char, fmt, iter, mem, str};
 
 #[allow(unused_macros)]
 macro_rules! write {
@@ -287,6 +287,84 @@ impl<'s> HexNibbles<'s> {
         }
         Some(v)
     }
+
+    /// Decode a UTF-8 byte sequence (with each byte using a pair of nibbles)
+    /// into individual `char`s, returning `None` for invalid UTF-8.
+    fn try_parse_str_chars(&self) -> Option<impl Iterator<Item = char> + 's> {
+        if self.nibbles.len() % 2 != 0 {
+            return None;
+        }
+
+        // FIXME(eddyb) use `array_chunks` instead, when that becomes stable.
+        let mut bytes = self
+            .nibbles
+            .as_bytes()
+            .chunks_exact(2)
+            .map(|slice| match slice {
+                [a, b] => [a, b],
+                _ => unreachable!(),
+            })
+            .map(|[&hi, &lo]| {
+                let half = |nibble: u8| (nibble as char).to_digit(16).unwrap() as u8;
+                (half(hi) << 4) | half(lo)
+            });
+
+        let chars = iter::from_fn(move || {
+            // As long as there are any bytes left, there's at least one more
+            // UTF-8-encoded `char` to decode (or the possibility of error).
+            bytes.next().map(|first_byte| -> Result<char, ()> {
+                // FIXME(eddyb) this `enum` and `fn` should be somewhere in `core`.
+                enum Utf8FirstByteError {
+                    ContinuationByte,
+                    TooLong,
+                }
+                fn utf8_len_from_first_byte(byte: u8) -> Result<usize, Utf8FirstByteError> {
+                    match byte {
+                        0x00..=0x7f => Ok(1),
+                        0x80..=0xbf => Err(Utf8FirstByteError::ContinuationByte),
+                        0xc0..=0xdf => Ok(2),
+                        0xe0..=0xef => Ok(3),
+                        0xf0..=0xf7 => Ok(4),
+                        0xf8..=0xff => Err(Utf8FirstByteError::TooLong),
+                    }
+                }
+
+                // Collect the appropriate amount of bytes (up to 4), according
+                // to the UTF-8 length implied by the first byte.
+                let utf8_len = utf8_len_from_first_byte(first_byte).map_err(|_| ())?;
+                let utf8 = &mut [first_byte, 0, 0, 0][..utf8_len];
+                for i in 1..utf8_len {
+                    utf8[i] = bytes.next().ok_or(())?;
+                }
+
+                // Fully validate the UTF-8 sequence.
+                let s = str::from_utf8(utf8).map_err(|_| ())?;
+
+                // Since we included exactly one UTF-8 sequence, and validation
+                // succeeded, `str::chars` should return exactly one `char`.
+                let mut chars = s.chars();
+                match (chars.next(), chars.next()) {
+                    (Some(c), None) => Ok(c),
+                    _ => unreachable!(
+                        "str::from_utf8({:?}) = {:?} was expected to have 1 char, \
+                         but {} chars were found",
+                        utf8,
+                        s,
+                        s.chars().count()
+                    ),
+                }
+            })
+        });
+
+        // HACK(eddyb) doing a separate validation iteration like this might be
+        // wasteful, but it's easier to avoid starting to print a string literal
+        // in the first place, than to abort it mid-string.
+        if chars.clone().any(|r| r.is_err()) {
+            None
+        } else {
+            Some(chars.map(Result::unwrap))
+        }
+    }
 }
 
 fn basic_type(tag: u8) -> Option<&'static str> {
@@ -815,7 +893,7 @@ impl<'a, 'b, 's> Printer<'a, 'b, 's> {
             let lt = parse!(self, integer_62);
             self.print_lifetime_from_index(lt)
         } else if self.eat(b'K') {
-            self.print_const()
+            self.print_const(false)
         } else {
             self.print_type()
         }
@@ -861,7 +939,7 @@ impl<'a, 'b, 's> Printer<'a, 'b, 's> {
                 self.print_type()?;
                 if tag == b'A' {
                     self.print("; ")?;
-                    self.print_const()?;
+                    self.print_const(true)?;
                 }
                 self.print("]")?;
             }
@@ -1001,11 +1079,28 @@ impl<'a, 'b, 's> Printer<'a, 'b, 's> {
         Ok(())
     }
 
-    fn print_const(&mut self) -> fmt::Result {
+    fn print_const(&mut self, in_value: bool) -> fmt::Result {
         let tag = parse!(self, next);
 
         parse!(self, push_depth);
 
+        // Only literals (and the names of `const` generic parameters, but they
+        // don't get mangled at all), can appear in generic argument position
+        // without any disambiguation, all other expressions require braces.
+        // To avoid duplicating the mapping between `tag` and what syntax gets
+        // used (especially any special-casing), every case that needs braces
+        // has to call `open_brace(self)?` (and the closing brace is automatic).
+        let mut opened_brace = false;
+        let mut open_brace_if_outside_expr = |this: &mut Self| {
+            // If this expression is nested in another, braces aren't required.
+            if in_value {
+                return Ok(());
+            }
+
+            opened_brace = true;
+            this.print("{")
+        };
+
         match tag {
             b'p' => self.print("_")?,
 
@@ -1033,13 +1128,82 @@ impl<'a, 'b, 's> Printer<'a, 'b, 's> {
                     None => invalid!(self),
                 }
             }
+            b'e' => {
+                // NOTE(eddyb) a string literal `"..."` has type `&str`, so
+                // to get back the type `str`, `*"..."` syntax is needed
+                // (even if that may not be valid in Rust itself).
+                open_brace_if_outside_expr(self)?;
+                self.print("*")?;
+
+                self.print_const_str_literal()?;
+            }
 
+            b'R' | b'Q' => {
+                // NOTE(eddyb) this prints `"..."` instead of `&*"..."`, which
+                // is what `Re..._` would imply (see comment for `str` above).
+                if tag == b'R' && self.eat(b'e') {
+                    self.print_const_str_literal()?;
+                } else {
+                    open_brace_if_outside_expr(self)?;
+                    self.print("&")?;
+                    if tag != b'R' {
+                        self.print("mut ")?;
+                    }
+                    self.print_const(true)?;
+                }
+            }
+            b'A' => {
+                open_brace_if_outside_expr(self)?;
+                self.print("[")?;
+                self.print_sep_list(|this| this.print_const(true), ", ")?;
+                self.print("]")?;
+            }
+            b'T' => {
+                open_brace_if_outside_expr(self)?;
+                self.print("(")?;
+                let count = self.print_sep_list(|this| this.print_const(true), ", ")?;
+                if count == 1 {
+                    self.print(",")?;
+                }
+                self.print(")")?;
+            }
+            b'V' => {
+                open_brace_if_outside_expr(self)?;
+                self.print_path(true)?;
+                match parse!(self, next) {
+                    b'U' => {}
+                    b'T' => {
+                        self.print("(")?;
+                        self.print_sep_list(|this| this.print_const(true), ", ")?;
+                        self.print(")")?;
+                    }
+                    b'S' => {
+                        self.print(" { ")?;
+                        self.print_sep_list(
+                            |this| {
+                                parse!(this, disambiguator);
+                                let name = parse!(this, ident);
+                                this.print(name)?;
+                                this.print(": ")?;
+                                this.print_const(true)
+                            },
+                            ", ",
+                        )?;
+                        self.print(" }")?;
+                    }
+                    _ => invalid!(self),
+                }
+            }
             b'B' => {
-                self.print_backref(Self::print_const)?;
+                self.print_backref(|this| this.print_const(in_value))?;
             }
             _ => invalid!(self),
         }
 
+        if opened_brace {
+            self.print("}")?;
+        }
+
         self.pop_depth();
         Ok(())
     }
@@ -1066,6 +1230,13 @@ impl<'a, 'b, 's> Printer<'a, 'b, 's> {
 
         Ok(())
     }
+
+    fn print_const_str_literal(&mut self) -> fmt::Result {
+        match parse!(self, hex_nibbles).try_parse_str_chars() {
+            Some(chars) => self.print_quoted_escaped_chars('"', chars),
+            None => invalid!(self),
+        }
+    }
 }
 
 #[cfg(test)]
@@ -1164,6 +1335,92 @@ mod tests {
         t_const!("c2202_", "'∂'");
     }
 
+    #[test]
+    fn demangle_const_str() {
+        t_const!("e616263_", "{*\"abc\"}");
+        t_const!("e27_", r#"{*"'"}"#);
+        t_const!("e090a_", "{*\"\\t\\n\"}");
+        t_const!("ee28882c3bc_", "{*\"∂ü\"}");
+        t_const!(
+            "ee183a1e18390e183ade1839be18394e1839ae18390e183935fe18392e18394e1839b\
+              e183a0e18398e18394e1839ae183985fe183a1e18390e18393e18398e1839ae18398_",
+            "{*\"საჭმელად_გემრიელი_სადილი\"}"
+        );
+        t_const!(
+            "ef09f908af09fa688f09fa686f09f90ae20c2a720f09f90b6f09f9192e298\
+              95f09f94a520c2a720f09fa7a1f09f929bf09f929af09f9299f09f929c_",
+            "{*\"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜\"}"
+        );
+    }
+
+    // NOTE(eddyb) this uses the same strings as `demangle_const_str` and should
+    // be kept in sync with it - while a macro could be used to generate both
+    // `str` and `&str` tests, from a single list of strings, this seems clearer.
+    #[test]
+    fn demangle_const_ref_str() {
+        t_const!("Re616263_", "\"abc\"");
+        t_const!("Re27_", r#""'""#);
+        t_const!("Re090a_", "\"\\t\\n\"");
+        t_const!("Ree28882c3bc_", "\"∂ü\"");
+        t_const!(
+            "Ree183a1e18390e183ade1839be18394e1839ae18390e183935fe18392e18394e1839b\
+               e183a0e18398e18394e1839ae183985fe183a1e18390e18393e18398e1839ae18398_",
+            "\"საჭმელად_გემრიელი_სადილი\""
+        );
+        t_const!(
+            "Ref09f908af09fa688f09fa686f09f90ae20c2a720f09f90b6f09f9192e298\
+               95f09f94a520c2a720f09fa7a1f09f929bf09f929af09f9299f09f929c_",
+            "\"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜\""
+        );
+    }
+
+    #[test]
+    fn demangle_const_ref() {
+        t_const!("Rp", "{&_}");
+        t_const!("Rh7b_", "{&123}");
+        t_const!("Rb0_", "{&false}");
+        t_const!("Rc58_", "{&'X'}");
+        t_const!("RRRh0_", "{&&&0}");
+        t_const!("RRRe_", "{&&\"\"}");
+        t_const!("QAE", "{&mut []}");
+    }
+
+    #[test]
+    fn demangle_const_array() {
+        t_const!("AE", "{[]}");
+        t_const!("Aj0_E", "{[0]}");
+        t_const!("Ah1_h2_h3_E", "{[1, 2, 3]}");
+        t_const!("ARe61_Re62_Re63_E", "{[\"a\", \"b\", \"c\"]}");
+        t_const!("AAh1_h2_EAh3_h4_EE", "{[[1, 2], [3, 4]]}");
+    }
+
+    #[test]
+    fn demangle_const_tuple() {
+        t_const!("TE", "{()}");
+        t_const!("Tj0_E", "{(0,)}");
+        t_const!("Th1_b0_E", "{(1, false)}");
+        t_const!(
+            "TRe616263_c78_RAh1_h2_h3_EE",
+            "{(\"abc\", 'x', &[1, 2, 3])}"
+        );
+    }
+
+    #[test]
+    fn demangle_const_adt() {
+        t_const!(
+            "VNvINtNtC4core6option6OptionjE4NoneU",
+            "{core::option::Option::<usize>::None}"
+        );
+        t_const!(
+            "VNvINtNtC4core6option6OptionjE4SomeTj0_E",
+            "{core::option::Option::<usize>::Some(0)}"
+        );
+        t_const!(
+            "VNtC3foo3BarS1sRe616263_2chc78_5sliceRAh1_h2_h3_EE",
+            "{foo::Bar { s: \"abc\", ch: 'x', slice: &[1, 2, 3] }}"
+        );
+    }
+
     #[test]
     fn demangle_exponential_explosion() {
         // NOTE(eddyb) because of the prefix added by `t_nohash_type!` is