Improve panic messages in parse_quote! by embedding location

src/discouraged.rs

@@ -167,7 +167,7 @@ pub trait Speculative {
 impl<'a> Speculative for ParseBuffer<'a> {
     fn advance_to(&self, fork: &Self) {
         if !crate::buffer::same_scope(self.cursor(), fork.cursor()) {
-            panic!("fork was not derived from the advancing parse stream");
+            crate::panic_with_location!("fork was not derived from the advancing parse stream");
         }
 
         let (self_unexp, self_sp) = inner_unexpected(self);

src/lib.rs

@@ -1013,3 +1013,25 @@ pub fn parse_file(mut content: &str) -> Result<File> {
     file.shebang = shebang;
     Ok(file)
 }
+
+/// `panic!` macro that includes location information [file:line:column]
+/// when inside of a proc-macro, because otherwise you don't get this information without
+/// -Zmacro-backtrace, and enabling it is an extra step which makes debugging proc macros harder
+macro_rules! panic_with_location {
+    ($message:literal $($tt:tt)*) => {{
+        #[cfg(feature = "proc-macro")]
+        let is_available = proc_macro::is_available();
+        #[cfg(not(feature = "proc-macro"))]
+        let is_available = false;
+        if is_available {
+            let location = core::panic::Location::caller();
+            let file = location.file();
+            let line = location.line();
+            let column = location.column();
+            ::core::panic!(concat!("[{}:{}:{}] ", $message), file, line, column $($tt)*)
+        } else {
+            ::core::panic!($message $($tt)*)
+        }
+    }};
+}
+pub(crate) use panic_with_location;

src/lifetime.rs

@@ -37,18 +37,18 @@ impl Lifetime {
     /// ```
     pub fn new(symbol: &str, span: Span) -> Self {
         if !symbol.starts_with('\'') {
-            panic!(
+            crate::panic_with_location!(
                 "lifetime name must start with apostrophe as in \"'a\", got {:?}",
                 symbol
             );
         }
 
         if symbol == "'" {
-            panic!("lifetime name must not be empty");
+            crate::panic_with_location!("lifetime name must not be empty");
         }
 
         if !crate::ident::xid_ok(&symbol[1..]) {
-            panic!("{:?} is not a valid lifetime name", symbol);
+            crate::panic_with_location!("{:?} is not a valid lifetime name", symbol);
         }
 
         Lifetime {

src/lit.rs

@@ -424,7 +424,7 @@ impl LitInt {
     pub fn new(repr: &str, span: Span) -> Self {
         let (digits, suffix) = match value::parse_lit_int(repr) {
             Some(parse) => parse,
-            None => panic!("not an integer literal: `{}`", repr),
+            None => crate::panic_with_location!("not an integer literal: `{}`", repr),
         };
 
         let mut token: Literal = repr.parse().unwrap();
@@ -504,7 +504,7 @@ impl From<Literal> for LitInt {
                 }),
             }
         } else {
-            panic!("not an integer literal: `{}`", repr);
+            crate::panic_with_location!("not an integer literal: `{}`", repr);
         }
     }
 }
@@ -520,7 +520,7 @@ impl LitFloat {
     pub fn new(repr: &str, span: Span) -> Self {
         let (digits, suffix) = match value::parse_lit_float(repr) {
             Some(parse) => parse,
-            None => panic!("not a float literal: `{}`", repr),
+            None => crate::panic_with_location!("not a float literal: `{}`", repr),
         };
 
         let mut token: Literal = repr.parse().unwrap();
@@ -578,7 +578,7 @@ impl From<Literal> for LitFloat {
                 }),
             }
         } else {
-            panic!("not a float literal: `{}`", repr);
+            crate::panic_with_location!("not a float literal: `{}`", repr);
         }
     }
 }

src/parse_quote.rs

@@ -133,7 +133,7 @@ pub fn parse<T: ParseQuote>(token_stream: TokenStream) -> T {
     let parser = T::parse;
     match parser.parse2(token_stream) {
         Ok(t) => t,
-        Err(err) => panic!("{}", err),
+        Err(err) => crate::panic_with_location!("{}", err),
     }
 }
 

src/punctuated.rs

@@ -504,7 +504,7 @@ where
     let mut nomore = false;
     for pair in i {
         if nomore {
-            panic!("punctuated extended with items after a Pair::End");
+            crate::panic_with_location!("punctuated extended with items after a Pair::End");
         }
         match pair {
             Pair::Punctuated(a, b) => punctuated.inner.push((a, b)),

src/verbatim.rs

@@ -22,7 +22,7 @@ pub(crate) fn between<'a>(begin: ParseStream<'a>, end: ParseStream<'a>) -> Token
                 cursor = inside;
                 continue;
             } else {
-                panic!("verbatim end must not be inside a delimited group");
+                crate::panic_with_location!("verbatim end must not be inside a delimited group");
             }
         }