Auto merge of #4274 - daxpedda:implicit_return_fixes, r=flip1995

false positives fixes of `implicit_return`

-  Handle returning macro statements properly (remove "this error originates in a macro outside of the current crate")
-  Handle functions that return never type
-  Handle functions that panic but do not return never type

changelog: Fix false positives in `implicit_return` lint pertaining to macros and panics

3 files changed, 118 insertions, 74 deletions

diff --git a/clippy_lints/src/implicit_return.rs b/clippy_lints/src/implicit_return.rs
index e280ce4c80b..4df9789f39d 100644
--- a/clippy_lints/src/implicit_return.rs
+++ b/clippy_lints/src/implicit_return.rs
@@ -1,7 +1,14 @@
-use crate::utils::{in_macro_or_desugar, is_expn_of, snippet_opt, span_lint_and_then};
-use rustc::hir::{intravisit::FnKind, Body, ExprKind, FnDecl, HirId, MatchSource};
-use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
-use rustc::{declare_lint_pass, declare_tool_lint};
+use crate::utils::{
+    in_macro_or_desugar, match_def_path,
+    paths::{BEGIN_PANIC, BEGIN_PANIC_FMT},
+    resolve_node, snippet_opt, span_lint_and_then,
+};
+use if_chain::if_chain;
+use rustc::{
+    declare_lint_pass, declare_tool_lint,
+    hir::{intravisit::FnKind, Body, Expr, ExprKind, FnDecl, HirId, MatchSource, StmtKind},
+    lint::{LateContext, LateLintPass, LintArray, LintPass},
+};
 use rustc_errors::Applicability;
 use syntax::source_map::Span;
 
@@ -35,71 +42,92 @@ declare_clippy_lint! {
 
 declare_lint_pass!(ImplicitReturn => [IMPLICIT_RETURN]);
 
-impl ImplicitReturn {
-    fn lint(cx: &LateContext<'_, '_>, outer_span: syntax_pos::Span, inner_span: syntax_pos::Span, msg: &str) {
-        span_lint_and_then(cx, IMPLICIT_RETURN, outer_span, "missing return statement", |db| {
-            if let Some(snippet) = snippet_opt(cx, inner_span) {
-                db.span_suggestion(
-                    outer_span,
-                    msg,
-                    format!("return {}", snippet),
-                    Applicability::MachineApplicable,
-                );
-            }
-        });
+static LINT_BREAK: &str = "change `break` to `return` as shown";
+static LINT_RETURN: &str = "add `return` as shown";
+
+fn lint(cx: &LateContext<'_, '_>, outer_span: Span, inner_span: Span, msg: &str) {
+    let outer_span = span_to_outer_expn(outer_span);
+    let inner_span = span_to_outer_expn(inner_span);
+
+    span_lint_and_then(cx, IMPLICIT_RETURN, outer_span, "missing return statement", |db| {
+        if let Some(snippet) = snippet_opt(cx, inner_span) {
+            db.span_suggestion(
+                outer_span,
+                msg,
+                format!("return {}", snippet),
+                Applicability::MachineApplicable,
+            );
+        }
+    });
+}
+
+fn span_to_outer_expn(span: Span) -> Span {
+    if let Some(expr) = span.ctxt().outer_expn_info() {
+        span_to_outer_expn(expr.call_site)
+    } else {
+        span
     }
+}
 
-    fn expr_match(cx: &LateContext<'_, '_>, expr: &rustc::hir::Expr) {
-        match &expr.node {
-            // loops could be using `break` instead of `return`
-            ExprKind::Block(block, ..) | ExprKind::Loop(block, ..) => {
-                if let Some(expr) = &block.expr {
-                    Self::expr_match(cx, expr);
-                }
-                // only needed in the case of `break` with `;` at the end
-                else if let Some(stmt) = block.stmts.last() {
-                    if let rustc::hir::StmtKind::Semi(expr, ..) = &stmt.node {
-                        // make sure it's a break, otherwise we want to skip
-                        if let ExprKind::Break(.., break_expr) = &expr.node {
-                            if let Some(break_expr) = break_expr {
-                                Self::lint(cx, expr.span, break_expr.span, "change `break` to `return` as shown");
-                            }
-                        }
+fn expr_match(cx: &LateContext<'_, '_>, expr: &Expr) {
+    match &expr.node {
+        // loops could be using `break` instead of `return`
+        ExprKind::Block(block, ..) | ExprKind::Loop(block, ..) => {
+            if let Some(expr) = &block.expr {
+                expr_match(cx, expr);
+            }
+            // only needed in the case of `break` with `;` at the end
+            else if let Some(stmt) = block.stmts.last() {
+                if_chain! {
+                    if let StmtKind::Semi(expr, ..) = &stmt.node;
+                    // make sure it's a break, otherwise we want to skip
+                    if let ExprKind::Break(.., break_expr) = &expr.node;
+                    if let Some(break_expr) = break_expr;
+                    then {
+                            lint(cx, expr.span, break_expr.span, LINT_BREAK);
                     }
                 }
-            },
-            // use `return` instead of `break`
-            ExprKind::Break(.., break_expr) => {
-                if let Some(break_expr) = break_expr {
-                    Self::lint(cx, expr.span, break_expr.span, "change `break` to `return` as shown");
-                }
-            },
-            ExprKind::Match(.., arms, source) => {
-                let check_all_arms = match source {
-                    MatchSource::IfLetDesugar {
-                        contains_else_clause: has_else,
-                    } => *has_else,
-                    _ => true,
-                };
+            }
+        },
+        // use `return` instead of `break`
+        ExprKind::Break(.., break_expr) => {
+            if let Some(break_expr) = break_expr {
+                lint(cx, expr.span, break_expr.span, LINT_BREAK);
+            }
+        },
+        ExprKind::Match(.., arms, source) => {
+            let check_all_arms = match source {
+                MatchSource::IfLetDesugar {
+                    contains_else_clause: has_else,
+                } => *has_else,
+                _ => true,
+            };
 
-                if check_all_arms {
-                    for arm in arms {
-                        Self::expr_match(cx, &arm.body);
-                    }
-                } else {
-                    Self::expr_match(cx, &arms.first().expect("if let doesn't have a single arm").body);
+            if check_all_arms {
+                for arm in arms {
+                    expr_match(cx, &arm.body);
                 }
-            },
-            // skip if it already has a return statement
-            ExprKind::Ret(..) => (),
-            // everything else is missing `return`
-            _ => {
-                // make sure it's not just an unreachable expression
-                if is_expn_of(expr.span, "unreachable").is_none() {
-                    Self::lint(cx, expr.span, expr.span, "add `return` as shown")
+            } else {
+                expr_match(cx, &arms.first().expect("if let doesn't have a single arm").body);
+            }
+        },
+        // skip if it already has a return statement
+        ExprKind::Ret(..) => (),
+        // make sure it's not a call that panics
+        ExprKind::Call(expr, ..) => {
+            if_chain! {
+                if let ExprKind::Path(qpath) = &expr.node;
+                if let Some(path_def_id) = resolve_node(cx, qpath, expr.hir_id).opt_def_id();
+                if match_def_path(cx, path_def_id, &BEGIN_PANIC) ||
+                    match_def_path(cx, path_def_id, &BEGIN_PANIC_FMT);
+                then { }
+                else {
+                    lint(cx, expr.span, expr.span, LINT_RETURN)
                 }
-            },
-        }
+            }
+        },
+        // everything else is missing `return`
+        _ => lint(cx, expr.span, expr.span, LINT_RETURN),
     }
 }
 
@@ -119,7 +147,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitReturn {
         // checking return type through MIR, HIR is not able to determine inferred closure return types
         // make sure it's not a macro
         if !mir.return_ty().is_unit() && !in_macro_or_desugar(span) {
-            Self::expr_match(cx, &body.value);
+            expr_match(cx, &body.value);
         }
     }
 }
diff --git a/tests/ui/implicit_return.rs b/tests/ui/implicit_return.rs
index d1c63ca1697..47e0679c430 100644
--- a/tests/ui/implicit_return.rs
+++ b/tests/ui/implicit_return.rs
@@ -5,6 +5,7 @@ fn test_end_of_fn() -> bool {
         // no error!
         return true;
     }
+
     true
 }
 
@@ -76,6 +77,14 @@ fn test_closure() {
     let _ = || true;
 }
 
+fn test_panic() -> bool {
+    panic!()
+}
+
+fn test_return_macro() -> String {
+    format!("test {}", "test")
+}
+
 fn main() {
     let _ = test_end_of_fn();
     let _ = test_if_block();
@@ -86,4 +95,5 @@ fn main() {
     let _ = test_loop_with_nests();
     let _ = test_loop_with_if_let();
     test_closure();
+    let _ = test_return_macro();
 }
diff --git a/tests/ui/implicit_return.stderr b/tests/ui/implicit_return.stderr
index 98b588f1a74..41b0873317e 100644
--- a/tests/ui/implicit_return.stderr
+++ b/tests/ui/implicit_return.stderr
@@ -1,5 +1,5 @@
 error: missing return statement
-  --> $DIR/implicit_return.rs:8:5
+  --> $DIR/implicit_return.rs:9:5
    |
 LL |     true
    |     ^^^^ help: add `return` as shown: `return true`
@@ -7,58 +7,64 @@ LL |     true
    = note: `-D clippy::implicit-return` implied by `-D warnings`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:14:9
+  --> $DIR/implicit_return.rs:15:9
    |
 LL |         true
    |         ^^^^ help: add `return` as shown: `return true`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:16:9
+  --> $DIR/implicit_return.rs:17:9
    |
 LL |         false
    |         ^^^^^ help: add `return` as shown: `return false`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:24:17
+  --> $DIR/implicit_return.rs:25:17
    |
 LL |         true => false,
    |                 ^^^^^ help: add `return` as shown: `return false`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:25:20
+  --> $DIR/implicit_return.rs:26:20
    |
 LL |         false => { true },
    |                    ^^^^ help: add `return` as shown: `return true`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:40:9
+  --> $DIR/implicit_return.rs:41:9
    |
 LL |         break true;
    |         ^^^^^^^^^^ help: change `break` to `return` as shown: `return true`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:48:13
+  --> $DIR/implicit_return.rs:49:13
    |
 LL |             break true;
    |             ^^^^^^^^^^ help: change `break` to `return` as shown: `return true`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:57:13
+  --> $DIR/implicit_return.rs:58:13
    |
 LL |             break true;
    |             ^^^^^^^^^^ help: change `break` to `return` as shown: `return true`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:75:18
+  --> $DIR/implicit_return.rs:76:18
    |
 LL |     let _ = || { true };
    |                  ^^^^ help: add `return` as shown: `return true`
 
 error: missing return statement
-  --> $DIR/implicit_return.rs:76:16
+  --> $DIR/implicit_return.rs:77:16
    |
 LL |     let _ = || true;
    |                ^^^^ help: add `return` as shown: `return true`
 
-error: aborting due to 10 previous errors
+error: missing return statement
+  --> $DIR/implicit_return.rs:85:5
+   |
+LL |     format!("test {}", "test")
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: add `return` as shown: `return format!("test {}", "test")`
+
+error: aborting due to 11 previous errors