Fix macro expansion in try_err lint

Author: tesuji

clippy_lints/src/try_err.rs

@@ -1,10 +1,11 @@
-use crate::utils::{match_qpath, paths, snippet, span_lint_and_sugg};
+use crate::utils::{in_macro_or_desugar, match_qpath, paths, snippet, span_lint_and_sugg};
 use if_chain::if_chain;
 use rustc::hir::*;
 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
 use rustc::ty::Ty;
 use rustc::{declare_lint_pass, declare_tool_lint};
 use rustc_errors::Applicability;
+use syntax::source_map::Span;
 
 declare_clippy_lint! {
     /// **What it does:** Checks for usages of `Err(x)?`.
@@ -67,10 +68,15 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TryErr {
 
             then {
                 let err_type = cx.tables.expr_ty(err_arg);
+                let span = if in_macro_or_desugar(err_arg.span) {
+                    span_to_outer_expn(err_arg.span)
+                } else {
+                    err_arg.span
+                };
                 let suggestion = if err_type == return_type {
-                    format!("return Err({})", snippet(cx, err_arg.span, "_"))
+                    format!("return Err({})", snippet(cx, span, "_"))
                 } else {
-                    format!("return Err({}.into())", snippet(cx, err_arg.span, "_"))
+                    format!("return Err({}.into())", snippet(cx, span, "_"))
                 };
 
                 span_lint_and_sugg(
@@ -87,6 +93,14 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TryErr {
     }
 }
 
+fn span_to_outer_expn(span: Span) -> Span {
+    let mut span = span;
+    while let Some(expr) = span.ctxt().outer_expn_info() {
+        span = expr.call_site;
+    }
+    span
+}
+
 // In order to determine whether to suggest `.into()` or not, we need to find the error type the
 // function returns. To do that, we look for the From::from call (see tree above), and capture
 // its output type.

tests/ui/try_err.fixed

@@ -78,3 +78,22 @@ fn main() {
     closure_matches_test().unwrap();
     closure_into_test().unwrap();
 }
+
+macro_rules! bar {
+    () => {
+        String::from("aasdfasdfasdfa")
+    };
+}
+
+macro_rules! foo {
+    () => {
+        bar!()
+    };
+}
+
+pub fn macro_inside(fail: bool) -> Result<i32, String> {
+    if fail {
+        return Err(foo!());
+    }
+    Ok(0)
+}

tests/ui/try_err.rs

@@ -78,3 +78,22 @@ fn main() {
     closure_matches_test().unwrap();
     closure_into_test().unwrap();
 }
+
+macro_rules! bar {
+    () => {
+        String::from("aasdfasdfasdfa")
+    };
+}
+
+macro_rules! foo {
+    () => {
+        bar!()
+    };
+}
+
+pub fn macro_inside(fail: bool) -> Result<i32, String> {
+    if fail {
+        Err(foo!())?;
+    }
+    Ok(0)
+}

tests/ui/try_err.stderr

@@ -28,5 +28,11 @@ error: returning an `Err(_)` with the `?` operator
 LL |                 Err(err)?;
    |                 ^^^^^^^^^ help: try this: `return Err(err.into())`
 
-error: aborting due to 4 previous errors
+error: returning an `Err(_)` with the `?` operator
+  --> $DIR/try_err.rs:96:9
+   |
+LL |         Err(foo!())?;
+   |         ^^^^^^^^^^^^ help: try this: `return Err(foo!())`
+
+error: aborting due to 5 previous errors