From 00a4ad198745b44751dad89c4e8409ac76d7b738 Mon Sep 17 00:00:00 2001
From: John-John Tedro <udoprog@tedro.se>
Date: Mon, 25 Sep 2023 18:12:03 +0200
Subject: [PATCH] Perform own detection for proc_macro_span (fixes #39)

---
 genco-macros/build.rs    | 35 ++++++++++++++++++++++++++++++
 genco-macros/src/fake.rs | 47 ++++++++++++++++++++++++++++------------
 genco-macros/src/lib.rs  |  1 +
 3 files changed, 69 insertions(+), 14 deletions(-)
 create mode 100644 genco-macros/build.rs

diff --git a/genco-macros/build.rs b/genco-macros/build.rs
new file mode 100644
index 0000000..b486454
--- /dev/null
+++ b/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 })
+}
diff --git a/genco-macros/src/fake.rs b/genco-macros/src/fake.rs
index a78ab91..1bcb5f7 100644
--- a/genco-macros/src/fake.rs
+++ b/genco-macros/src/fake.rs
@@ -17,12 +17,35 @@ pub(crate) struct LineColumn {
 }
 
 impl LineColumn {
-    fn new(line_column: proc_macro2::LineColumn) -> Self {
+    #[cfg(proc_macro_span)]
+    fn from_start(span: Span) -> Self {
+        let span = span.unwrap().start();
+
         Self {
-            line: line_column.line,
-            column: line_column.column,
+            line: span.line(),
+            column: span.column(),
         }
     }
+
+    #[cfg(proc_macro_span)]
+    fn from_end(span: Span) -> Self {
+        let span = span.unwrap().end();
+
+        Self {
+            line: span.line(),
+            column: span.column(),
+        }
+    }
+
+    #[cfg(not(proc_macro_span))]
+    fn from_start(span: Span) -> Self {
+        Self { line: 0, column: 0 }
+    }
+
+    #[cfg(not(proc_macro_span))]
+    fn from_end(span: Span) -> Self {
+        Self { line: 0, column: 0 }
+    }
 }
 
 #[derive(Default)]
@@ -42,8 +65,8 @@ impl Buf {
 
     /// 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();
+        let start = LineColumn::from_start(span);
+        let end = LineColumn::from_end(span);
 
         if (start.line == 0 && start.column == 0) || (end.line == 0 && end.column == 0) {
             // Try compat.
@@ -61,17 +84,13 @@ impl Buf {
                 },
             ))
         } else {
-            Ok(Cursor::new(
-                span,
-                LineColumn::new(start),
-                LineColumn::new(end),
-            ))
+            Ok(Cursor::new(span, start, end))
         }
     }
 
     /// The start of the given span.
     pub(crate) fn start(&mut self, span: Span) -> syn::Result<LineColumn> {
-        let start = span.start();
+        let start = LineColumn::from_start(span);
 
         // Try to use compat layer.
         if start.line == 0 && start.column == 0 {
@@ -79,13 +98,13 @@ impl Buf {
             let (column, _) = self.find_line_column(span)?;
             Ok(LineColumn { line: 1, column })
         } else {
-            Ok(LineColumn::new(start))
+            Ok(start)
         }
     }
 
     /// The start of the given span.
     pub(crate) fn end(&mut self, span: Span) -> syn::Result<LineColumn> {
-        let end = span.end();
+        let end = LineColumn::from_end(span);
 
         // Try to use compat layer.
         if end.line == 0 && end.column == 0 {
@@ -93,7 +112,7 @@ impl Buf {
             let (_, column) = self.find_line_column(span)?;
             Ok(LineColumn { line: 1, column })
         } else {
-            Ok(LineColumn::new(end))
+            Ok(end)
         }
     }
 
diff --git a/genco-macros/src/lib.rs b/genco-macros/src/lib.rs
index 6d7b5c5..7a9a68c 100644
--- a/genco-macros/src/lib.rs
+++ b/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;