Auto merge of #4635 - Lythenas:suggestions-for-assert-false, r=flip1995

Add assert message to suggestion in lint assertions_on_constants

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- [x] suggest replacing `assert!(false, "msg")` with `panic!("msg")`
- [x] extend to allow ~~variables~~ any expression for `"msg"`
- ~~suggest replacing `assert!(false, "msg {}", "arg")` with `panic!("msg {}", "arg")`~~

changelog: add assert message to suggestion in lint assertions_on_constants

Work towards fixing: #3575

Author: bors

clippy_lints/src/assertions_on_constants.rs

@@ -1,9 +1,11 @@
-use rustc::hir::{Expr, ExprKind};
+use crate::consts::{constant, Constant};
+use crate::utils::paths;
+use crate::utils::{is_direct_expn_of, is_expn_of, match_def_path, snippet_opt, span_help_and_lint};
+use if_chain::if_chain;
+use rustc::hir::*;
 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
 use rustc::{declare_lint_pass, declare_tool_lint};
-
-use crate::consts::{constant, Constant};
-use crate::utils::{is_direct_expn_of, is_expn_of, span_help_and_lint};
+use syntax::ast::LitKind;
 
 declare_clippy_lint! {
     /// **What it does:** Checks for `assert!(true)` and `assert!(false)` calls.
@@ -31,39 +33,135 @@ declare_lint_pass!(AssertionsOnConstants => [ASSERTIONS_ON_CONSTANTS]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssertionsOnConstants {
     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
-        let lint_assert_cb = |is_debug_assert: bool| {
-            if let ExprKind::Unary(_, ref lit) = e.kind {
-                if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.tables, lit) {
-                    if is_true {
-                        span_help_and_lint(
-                            cx,
-                            ASSERTIONS_ON_CONSTANTS,
-                            e.span,
-                            "`assert!(true)` will be optimized out by the compiler",
-                            "remove it",
-                        );
-                    } else if !is_debug_assert {
-                        span_help_and_lint(
-                            cx,
-                            ASSERTIONS_ON_CONSTANTS,
-                            e.span,
-                            "`assert!(false)` should probably be replaced",
-                            "use `panic!()` or `unreachable!()`",
-                        );
-                    }
-                }
-            }
+        let lint_true = || {
+            span_help_and_lint(
+                cx,
+                ASSERTIONS_ON_CONSTANTS,
+                e.span,
+                "`assert!(true)` will be optimized out by the compiler",
+                "remove it",
+            );
         };
+        let lint_false_without_message = || {
+            span_help_and_lint(
+                cx,
+                ASSERTIONS_ON_CONSTANTS,
+                e.span,
+                "`assert!(false)` should probably be replaced",
+                "use `panic!()` or `unreachable!()`",
+            );
+        };
+        let lint_false_with_message = |panic_message: String| {
+            span_help_and_lint(
+                cx,
+                ASSERTIONS_ON_CONSTANTS,
+                e.span,
+                &format!("`assert!(false, {})` should probably be replaced", panic_message),
+                &format!("use `panic!({})` or `unreachable!({})`", panic_message, panic_message),
+            )
+        };
+
         if let Some(debug_assert_span) = is_expn_of(e.span, "debug_assert") {
             if debug_assert_span.from_expansion() {
                 return;
             }
-            lint_assert_cb(true);
+            if_chain! {
+                if let ExprKind::Unary(_, ref lit) = e.kind;
+                if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.tables, lit);
+                if is_true;
+                then {
+                    lint_true();
+                }
+            };
         } else if let Some(assert_span) = is_direct_expn_of(e.span, "assert") {
             if assert_span.from_expansion() {
                 return;
             }
-            lint_assert_cb(false);
+            if let Some(assert_match) = match_assert_with_message(&cx, e) {
+                match assert_match {
+                    // matched assert but not message
+                    AssertKind::WithoutMessage(false) => lint_false_without_message(),
+                    AssertKind::WithoutMessage(true) | AssertKind::WithMessage(_, true) => lint_true(),
+                    AssertKind::WithMessage(panic_message, false) => lint_false_with_message(panic_message),
+                };
+            }
         }
     }
 }
+
+/// Result of calling `match_assert_with_message`.
+enum AssertKind {
+    WithMessage(String, bool),
+    WithoutMessage(bool),
+}
+
+/// Check if the expression matches
+///
+/// ```rust,ignore
+/// match { let _t = !c; _t } {
+///     true => {
+///         {
+///             ::std::rt::begin_panic(message, _)
+///         }
+///     }
+///     _ => { }
+/// };
+/// ```
+///
+/// where `message` is any expression and `c` is a constant bool.
+fn match_assert_with_message<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> Option<AssertKind> {
+    if_chain! {
+        if let ExprKind::Match(ref expr, ref arms, _) = expr.kind;
+        // matches { let _t = expr; _t }
+        if let ExprKind::DropTemps(ref expr) = expr.kind;
+        if let ExprKind::Unary(UnOp::UnNot, ref expr) = expr.kind;
+        // bind the first argument of the `assert!` macro
+        if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.tables, expr);
+        // arm 1 pattern
+        if let PatKind::Lit(ref lit_expr) = arms[0].pat.kind;
+        if let ExprKind::Lit(ref lit) = lit_expr.kind;
+        if let LitKind::Bool(true) = lit.node;
+        // arm 1 block
+        if let ExprKind::Block(ref block, _) = arms[0].body.kind;
+        if block.stmts.len() == 0;
+        if let Some(block_expr) = &block.expr;
+        if let ExprKind::Block(ref inner_block, _) = block_expr.kind;
+        if let Some(begin_panic_call) = &inner_block.expr;
+        // function call
+        if let Some(args) = match_function_call(cx, begin_panic_call, &paths::BEGIN_PANIC);
+        if args.len() == 2;
+        // bind the second argument of the `assert!` macro if it exists
+        if let panic_message = snippet_opt(cx, args[0].span);
+        // second argument of begin_panic is irrelevant
+        // as is the second match arm
+        then {
+            // an empty message occurs when it was generated by the macro
+            // (and not passed by the user)
+            return panic_message
+                .filter(|msg| !msg.is_empty())
+                .map(|msg| AssertKind::WithMessage(msg, is_true))
+                .or(Some(AssertKind::WithoutMessage(is_true)));
+        }
+    }
+    None
+}
+
+/// Matches a function call with the given path and returns the arguments.
+///
+/// Usage:
+///
+/// ```rust,ignore
+/// if let Some(args) = match_function_call(cx, begin_panic_call, &paths::BEGIN_PANIC);
+/// ```
+fn match_function_call<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, path: &[&str]) -> Option<&'a [Expr]> {
+    if_chain! {
+        if let ExprKind::Call(ref fun, ref args) = expr.kind;
+        if let ExprKind::Path(ref qpath) = fun.kind;
+        if let Some(fun_def_id) = cx.tables.qpath_res(qpath, fun.hir_id).opt_def_id();
+        if match_def_path(cx, fun_def_id, path);
+        then {
+            return Some(&args)
+        }
+    };
+    None
+}

tests/ui/assertions_on_constants.rs

@@ -11,11 +11,15 @@ fn main() {
     assert!(true, "true message");
     assert!(false, "false message");
 
+    let msg = "panic message";
+    assert!(false, msg.to_uppercase());
+
     const B: bool = true;
     assert!(B);
 
     const C: bool = false;
     assert!(C);
+    assert!(C, "C message");
 
     debug_assert!(true);
     // Don't lint this, since there is no better way for expressing "Only panic in debug mode".

tests/ui/assertions_on_constants.stderr

@@ -23,38 +23,54 @@ LL |     assert!(true, "true message");
    |
    = help: remove it
 
-error: `assert!(false)` should probably be replaced
+error: `assert!(false, "false message")` should probably be replaced
   --> $DIR/assertions_on_constants.rs:12:5
    |
 LL |     assert!(false, "false message");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: use `panic!()` or `unreachable!()`
+   = help: use `panic!("false message")` or `unreachable!("false message")`
 
-error: `assert!(true)` will be optimized out by the compiler
+error: `assert!(false, msg.to_uppercase())` should probably be replaced
   --> $DIR/assertions_on_constants.rs:15:5
    |
+LL |     assert!(false, msg.to_uppercase());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `panic!(msg.to_uppercase())` or `unreachable!(msg.to_uppercase())`
+
+error: `assert!(true)` will be optimized out by the compiler
+  --> $DIR/assertions_on_constants.rs:18:5
+   |
 LL |     assert!(B);
    |     ^^^^^^^^^^^
    |
    = help: remove it
 
 error: `assert!(false)` should probably be replaced
-  --> $DIR/assertions_on_constants.rs:18:5
+  --> $DIR/assertions_on_constants.rs:21:5
    |
 LL |     assert!(C);
    |     ^^^^^^^^^^^
    |
    = help: use `panic!()` or `unreachable!()`
 
+error: `assert!(false, "C message")` should probably be replaced
+  --> $DIR/assertions_on_constants.rs:22:5
+   |
+LL |     assert!(C, "C message");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `panic!("C message")` or `unreachable!("C message")`
+
 error: `assert!(true)` will be optimized out by the compiler
-  --> $DIR/assertions_on_constants.rs:20:5
+  --> $DIR/assertions_on_constants.rs:24:5
    |
 LL |     debug_assert!(true);
    |     ^^^^^^^^^^^^^^^^^^^^
    |
    = help: remove it
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
-error: aborting due to 7 previous errors
+error: aborting due to 9 previous errors