rust-lang · bors · Feb 25, 2019 · Feb 24, 2019
diff --git a/ci/base-tests.sh b/ci/base-tests.sh
@@ -59,7 +59,7 @@ rustup override set nightly
 # avoid loop spam and allow cmds with exit status != 0
 set +ex
 
-for file in `find tests -not -path "tests/ui/format.rs" -not -path "tests/ui/formatting.rs" -not -path "tests/ui/empty_line_after_outer_attribute.rs" -not -path "tests/ui/double_parens.rs" -not -path "tests/ui/doc.rs" -not -path "tests/ui/unused_unit.rs" | grep "\.rs$"` ; do
+for file in `find tests -not -path "tests/ui/formatting.rs" -not -path "tests/ui/empty_line_after_outer_attribute.rs" -not -path "tests/ui/double_parens.rs" -not -path "tests/ui/doc.rs" -not -path "tests/ui/unused_unit.rs" | grep "\.rs$"` ; do
   rustfmt ${file} --check
   if [ $? -ne 0 ]; then
     echo "${file} needs reformatting!"

diff --git a/clippy_lints/src/format.rs b/clippy_lints/src/format.rs
@@ -5,11 +5,12 @@ use crate::utils::{
 };
 use if_chain::if_chain;
 use rustc::hir::*;
-use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
+use rustc::lint::{LateContext, LateLintPass, LintArray, LintContext, LintPass};
 use rustc::ty;
 use rustc::{declare_tool_lint, lint_array};
 use rustc_errors::Applicability;
 use syntax::ast::LitKind;
+use syntax::source_map::Span;
 
 /// **What it does:** Checks for the use of `format!("string literal with no
 /// argument")` and `format!("{}", foo)` where `foo` is a string.
@@ -82,14 +83,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
                                 }
                             };
 
-                            span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
-                                db.span_suggestion(
-                                    expr.span,
-                                    message,
-                                    sugg,
-                                    Applicability::MachineApplicable,
-                                );
-                            });
+                            span_useless_format(cx, span, message, sugg);
                         }
                     }
                 },
@@ -98,14 +92,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
                     if let ExprKind::Tup(ref tup) = matchee.node {
                         if tup.is_empty() {
                             let sugg = format!("{}.to_string()", snippet(cx, expr.span, "<expr>").into_owned());
-                            span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
-                                db.span_suggestion(
-                                    span,
-                                    "consider using .to_string()",
-                                    sugg,
-                                    Applicability::MachineApplicable, // snippet
-                                );
-                            });
+                            span_useless_format(cx, span, "consider using .to_string()", sugg);
                         }
                     }
                 },
@@ -115,6 +102,25 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
     }
 }
 
+fn span_useless_format<'a, 'tcx: 'a, T: LintContext<'tcx>>(cx: &'a T, span: Span, help: &str, mut sugg: String) {
+    let to_replace = span.source_callsite();
+
+    // The callsite span contains the statement semicolon for some reason.
+    let snippet = snippet(cx, to_replace, "..");
+    if snippet.ends_with(';') {
+        sugg.push(';');
+    }
+
+    span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
+        db.span_suggestion(
+            to_replace,
+            help,
+            sugg,
+            Applicability::MachineApplicable, // snippet
+        );
+    });
+}
+
 /// Checks if the expressions matches `&[""]`
 fn check_single_piece(expr: &Expr) -> bool {
     if_chain! {

diff --git a/tests/ui/format.fixed b/tests/ui/format.fixed
@@ -0,0 +1,60 @@
+// run-rustfix
+
+#![allow(clippy::print_literal)]
+#![warn(clippy::useless_format)]
+
+struct Foo(pub String);
+
+macro_rules! foo {
+  ($($t:tt)*) => (Foo(format!($($t)*)))
+}
+
+fn main() {
+    "foo".to_string();
+
+    "foo".to_string();
+    format!("{:?}", "foo"); // don't warn about debug
+    format!("{:8}", "foo");
+    format!("{:width$}", "foo", width = 8);
+    "foo".to_string(); // warn when the format makes no difference
+    "foo".to_string(); // warn when the format makes no difference
+    format!("foo {}", "bar");
+    format!("{} bar", "foo");
+
+    let arg: String = "".to_owned();
+    arg.to_string();
+    format!("{:?}", arg); // don't warn about debug
+    format!("{:8}", arg);
+    format!("{:width$}", arg, width = 8);
+    arg.to_string(); // warn when the format makes no difference
+    arg.to_string(); // warn when the format makes no difference
+    format!("foo {}", arg);
+    format!("{} bar", arg);
+
+    // we don’t want to warn for non-string args, see #697
+    format!("{}", 42);
+    format!("{:?}", 42);
+    format!("{:+}", 42);
+    format!("foo {}", 42);
+    format!("{} bar", 42);
+
+    // we only want to warn about `format!` itself
+    println!("foo");
+    println!("{}", "foo");
+    println!("foo {}", "foo");
+    println!("{}", 42);
+    println!("foo {}", 42);
+
+    // A format! inside a macro should not trigger a warning
+    foo!("should not warn");
+
+    // precision on string means slicing without panicking on size:
+    format!("{:.1}", "foo"); // could be "foo"[..1]
+    format!("{:.10}", "foo"); // could not be "foo"[..10]
+    format!("{:.prec$}", "foo", prec = 1);
+    format!("{:.prec$}", "foo", prec = 10);
+
+    42.to_string();
+    let x = std::path::PathBuf::from("/bar/foo/qux");
+    x.display().to_string();
+}
diff --git a/tests/ui/format.rs b/tests/ui/format.rs
@@ -1,3 +1,5 @@
+// run-rustfix
+
 #![allow(clippy::print_literal)]
 #![warn(clippy::useless_format)]
 

diff --git a/tests/ui/format.stderr b/tests/ui/format.stderr
@@ -1,74 +1,58 @@
 error: useless use of `format!`
-  --> $DIR/format.rs:11:5
+  --> $DIR/format.rs:13:5
    |
 LL |     format!("foo");
-   |     ^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
+   |     ^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string();`
    |
    = note: `-D clippy::useless-format` implied by `-D warnings`
 
 error: useless use of `format!`
-  --> $DIR/format.rs:13:5
+  --> $DIR/format.rs:15:5
    |
 LL |     format!("{}", "foo");
-   |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string();`
 
 error: useless use of `format!`
-  --> $DIR/format.rs:17:5
+  --> $DIR/format.rs:19:5
    |
 LL |     format!("{:+}", "foo"); // warn when the format makes no difference
-   |     ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string();`
 
 error: useless use of `format!`
-  --> $DIR/format.rs:18:5
+  --> $DIR/format.rs:20:5
    |
 LL |     format!("{:<}", "foo"); // warn when the format makes no difference
-   |     ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string();`
 
 error: useless use of `format!`
-  --> $DIR/format.rs:23:5
+  --> $DIR/format.rs:25:5
    |
 LL |     format!("{}", arg);
-   |     ^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |     ^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string();`
 
 error: useless use of `format!`
-  --> $DIR/format.rs:27:5
+  --> $DIR/format.rs:29:5
    |
 LL |     format!("{:+}", arg); // warn when the format makes no difference
-   |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string();`
 
 error: useless use of `format!`
-  --> $DIR/format.rs:28:5
+  --> $DIR/format.rs:30:5
    |
 LL |     format!("{:<}", arg); // warn when the format makes no difference
-   |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string();`
 
 error: useless use of `format!`
-  --> $DIR/format.rs:55:5
+  --> $DIR/format.rs:57:5
    |
 LL |     format!("{}", 42.to_string());
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: `to_string()` is enough: `42.to_string()`
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: `to_string()` is enough: `42.to_string();`
 
 error: useless use of `format!`
-  --> $DIR/format.rs:57:5
+  --> $DIR/format.rs:59:5
    |
 LL |     format!("{}", x.display().to_string());
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: `to_string()` is enough: `x.display().to_string()`
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: `to_string()` is enough: `x.display().to_string();`
 
 error: aborting due to 9 previous errors