Perform own detection for proc_macro_span (fixes #39)

Author: udoprog

examples/java_string.rs

@@ -0,0 +1,7 @@
+use genco::prelude::*;
+
+fn main() -> Result<(), genco::fmt::Error> {
+    let tokens: python::Tokens = quote!($[str](Hello World));
+    assert_eq!("\"Hello World\"", tokens.to_string()?);
+    Ok::<_, genco::fmt::Error>(())
+}

genco-macros/build.rs

@@ -0,0 +1,35 @@
+use std::env;
+use std::process::Command;
+use std::str;
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    let version = rustc_version().unwrap_or(RustcVersion {
+        minor: u32::MAX,
+        nightly: false,
+    });
+
+    if version.nightly {
+        println!("cargo:rustc-cfg=proc_macro_span");
+    }
+}
+
+struct RustcVersion {
+    #[allow(unused)]
+    minor: u32,
+    nightly: bool,
+}
+
+fn rustc_version() -> Option<RustcVersion> {
+    let rustc = env::var_os("RUSTC")?;
+    let output = Command::new(rustc).arg("--version").output().ok()?;
+    let version = str::from_utf8(&output.stdout).ok()?;
+    let nightly = version.contains("nightly") || version.contains("dev");
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    let minor = pieces.next()?.parse().ok()?;
+    Some(RustcVersion { minor, nightly })
+}

genco-macros/src/fake.rs

@@ -1,3 +1,4 @@
+use std::cell::{RefCell, RefMut};
 use std::fmt::Arguments;
 
 use proc_macro2::Span;
@@ -17,84 +18,97 @@ pub(crate) struct LineColumn {
 }
 
 impl LineColumn {
-    fn new(line_column: proc_macro2::LineColumn) -> Self {
-        Self {
-            line: line_column.line,
-            column: line_column.column,
-        }
+    #[cfg(proc_macro_span)]
+    pub(crate) fn start(span: Span) -> Option<Self> {
+        let span = span.unwrap().start();
+
+        Some(Self {
+            line: span.line(),
+            column: span.column(),
+        })
+    }
+
+    #[cfg(proc_macro_span)]
+    pub(crate) fn end(span: Span) -> Option<Self> {
+        let span = span.unwrap().end();
+
+        Some(Self {
+            line: span.line(),
+            column: span.column(),
+        })
+    }
+
+    #[cfg(not(proc_macro_span))]
+    pub(crate) fn start(_: Span) -> Option<Self> {
+        None
+    }
+
+    #[cfg(not(proc_macro_span))]
+    pub(crate) fn end(_: Span) -> Option<Self> {
+        None
     }
 }
 
 #[derive(Default)]
 pub(crate) struct Buf {
-    buf: Option<String>,
+    buf: RefCell<String>,
 }
 
 impl Buf {
     /// Format the given arguments and return the associated string.
-    fn format(&mut self, args: Arguments<'_>) -> &str {
+    fn format(&self, args: Arguments<'_>) -> RefMut<'_, str> {
         use std::fmt::Write;
-        let buf = self.buf.get_or_insert_with(String::default);
+        let mut buf = self.buf.borrow_mut();
         buf.clear();
         buf.write_fmt(args).unwrap();
-        buf.as_str()
+        RefMut::map(buf, |buf| buf.as_mut_str())
     }
 
     /// Construct a cursor from a span.
-    pub(crate) fn cursor(&mut self, span: Span) -> syn::Result<Cursor> {
-        let start = span.start();
-        let end = span.end();
-
-        if (start.line == 0 && start.column == 0) || (end.line == 0 && end.column == 0) {
-            // Try compat.
-            let (start, end) = self.find_line_column(span)?;
-
-            Ok(Cursor::new(
-                span,
-                LineColumn {
-                    line: 1,
-                    column: start,
-                },
-                LineColumn {
-                    line: 1,
-                    column: end,
-                },
-            ))
-        } else {
-            Ok(Cursor::new(
-                span,
-                LineColumn::new(start),
-                LineColumn::new(end),
-            ))
+    pub(crate) fn cursor(&self, span: Span) -> syn::Result<Cursor> {
+        let start = LineColumn::start(span);
+        let end = LineColumn::end(span);
+
+        if let (Some(start), Some(end)) = (start, end) {
+            return Ok(Cursor::new(span, start, end));
         }
+
+        // Try compat.
+        let (start, end) = self.find_line_column(span)?;
+
+        Ok(Cursor::new(
+            span,
+            LineColumn {
+                line: 1,
+                column: start,
+            },
+            LineColumn {
+                line: 1,
+                column: end,
+            },
+        ))
     }
 
     /// The start of the given span.
     pub(crate) fn start(&mut self, span: Span) -> syn::Result<LineColumn> {
-        let start = span.start();
-
-        // Try to use compat layer.
-        if start.line == 0 && start.column == 0 {
-            // Try compat.
-            let (column, _) = self.find_line_column(span)?;
-            Ok(LineColumn { line: 1, column })
-        } else {
-            Ok(LineColumn::new(start))
+        if let Some(start) = LineColumn::start(span) {
+            return Ok(start);
         }
+
+        // Try compat.
+        let (column, _) = self.find_line_column(span)?;
+        Ok(LineColumn { line: 1, column })
     }
 
     /// The start of the given span.
     pub(crate) fn end(&mut self, span: Span) -> syn::Result<LineColumn> {
-        let end = span.end();
-
-        // Try to use compat layer.
-        if end.line == 0 && end.column == 0 {
-            // Try compat.
-            let (_, column) = self.find_line_column(span)?;
-            Ok(LineColumn { line: 1, column })
-        } else {
-            Ok(LineColumn::new(end))
+        if let Some(end) = LineColumn::end(span) {
+            return Ok(end);
         }
+
+        // Try compat.
+        let (_, column) = self.find_line_column(span)?;
+        Ok(LineColumn { line: 1, column })
     }
 
     /// Join two spans.
@@ -108,14 +122,14 @@ impl Buf {
 
     /// Try to decode line and column information using the debug implementation of
     /// a `span` which leaks the byte offset of a thing.
-    fn find_line_column(&mut self, span: Span) -> syn::Result<(usize, usize)> {
+    fn find_line_column(&self, span: Span) -> syn::Result<(usize, usize)> {
         match self.find_line_column_inner(span) {
             Some((start, end)) => Ok((start, end)),
             None => Err(syn::Error::new(span, ERROR)),
         }
     }
 
-    fn find_line_column_inner(&mut self, span: Span) -> Option<(usize, usize)> {
+    fn find_line_column_inner(&self, span: Span) -> Option<(usize, usize)> {
         let text = self.format(format_args!("{:?}", span));
         let start = text.find('(')?;
         let (start, end) = text

genco-macros/src/lib.rs

@@ -4,6 +4,7 @@
 
 #![recursion_limit = "256"]
 #![allow(clippy::type_complexity)]
+#![cfg_attr(proc_macro_span, feature(proc_macro_span))]
 
 extern crate proc_macro;
 

genco-macros/src/quote.rs

@@ -348,7 +348,7 @@ impl<'a> Quote<'a> {
                         ));
                     }
                     (LiteralName::Ident("str"), Some(content)) => {
-                        let parser = StringParser::new(self.receiver, end);
+                        let parser = StringParser::new(self.receiver, &self.buf, end)?;
 
                         let (options, r, stream) = parser.parse(&content)?;
                         encoder.requirements.merge_with(r);

genco-macros/src/string_parser.rs

@@ -1,9 +1,11 @@
 //! Helper to parse quoted strings.
 
 use crate::ast::LiteralName;
+use crate::fake::{Buf, LineColumn};
 use crate::quote::parse_internal_function;
 use crate::requirements::Requirements;
-use proc_macro2::{LineColumn, Span, TokenStream, TokenTree};
+
+use proc_macro2::{Span, TokenStream, TokenTree};
 use syn::parse::ParseStream;
 use syn::spanned::Spanned;
 use syn::token;
@@ -194,22 +196,26 @@ impl<'a> Encoder<'a> {
 
 pub struct StringParser<'a> {
     receiver: &'a syn::Ident,
+    buf: &'a Buf,
     start: LineColumn,
     end: LineColumn,
     span: Span,
 }
 
 impl<'a> StringParser<'a> {
-    pub(crate) fn new(receiver: &'a syn::Ident, span: Span) -> Self {
-        Self {
+    pub(crate) fn new(receiver: &'a syn::Ident, buf: &'a Buf, span: Span) -> syn::Result<Self> {
+        let cursor = buf.cursor(span)?;
+
+        Ok(Self {
             receiver,
+            buf,
             // Note: adjusting span since we expect the quoted string to be
             // withing a block, where the interior span is one character pulled
             // in in each direction.
-            start: adjust_start(span.start()),
-            end: adjust_end(span.end()),
+            start: adjust_start(cursor.start),
+            end: adjust_end(cursor.end),
             span,
-        }
+        })
     }
 
     pub(crate) fn parse(self, input: ParseStream) -> Result<(Options, Requirements, TokenStream)> {
@@ -220,23 +226,28 @@ impl<'a> StringParser<'a> {
             if input.peek(syn::Token![$]) && input.peek2(syn::Token![$]) {
                 let start = input.parse::<syn::Token![$]>()?;
                 let escape = input.parse::<syn::Token![$]>()?;
-                encoder.encode_char('$', start.span().start(), escape.span().end())?;
+                let start = self.buf.cursor(start.span())?;
+                let escape = self.buf.cursor(escape.span())?;
+                encoder.encode_char('$', start.start, escape.end)?;
                 continue;
             }
 
             if input.peek(syn::Token![$]) {
                 if let Some((name, content, [start, end])) = parse_internal_function(input)? {
                     match (name.as_literal_name(), content) {
                         (LiteralName::Ident("const"), Some(content)) => {
+                            let start = self.buf.cursor(start)?;
+                            let end = self.buf.cursor(end)?;
+
                             // Compile-time string optimization. A single,
                             // enclosed literal string can be added to the
                             // existing static buffer.
                             if content.peek(syn::LitStr) && content.peek2(crate::token::Eof) {
                                 let s = content.parse::<syn::LitStr>()?;
-                                encoder.encode_str(&s.value(), start.start(), Some(end.end()))?;
+                                encoder.encode_str(&s.value(), start.start, Some(end.end))?;
                             } else {
                                 let expr = content.parse::<syn::Expr>()?;
-                                encoder.raw_expr(&expr, start.start(), Some(end.end()))?;
+                                encoder.raw_expr(&expr, start.start, Some(end.end))?;
                             }
                         }
                         (literal_name, _) => {
@@ -254,7 +265,9 @@ impl<'a> StringParser<'a> {
 
                     if !input.peek(token::Paren) {
                         let ident = input.parse::<syn::Ident>()?;
-                        encoder.eval_ident(&ident, start.start(), Some(ident.span().end()))?;
+                        let start = self.buf.cursor(start.span())?;
+                        let end = self.buf.cursor(ident.span())?.end;
+                        encoder.eval_ident(&ident, start.start, Some(end))?;
                         continue;
                     }
 
@@ -265,14 +278,17 @@ impl<'a> StringParser<'a> {
                         .with_span(content.span())?
                         .parse(&content)?;
                     requirements.merge_with(req);
-                    encoder.eval_stream(stream, start.start(), Some(end.end()))?;
+                    let start = self.buf.cursor(start.span())?;
+                    let end = self.buf.cursor(end.span())?;
+                    encoder.eval_stream(stream, start.start, Some(end.end))?;
                 }
 
                 continue;
             }
 
             let tt = input.parse::<TokenTree>()?;
-            encoder.extend_tt(&tt, tt.span().start(), Some(tt.span().end()))?;
+            let cursor = self.buf.cursor(tt.span())?;
+            encoder.extend_tt(&tt, cursor.start, Some(cursor.end))?;
         }
 
         let (options, stream) = encoder.finalize(self.end)?;