Fix escaping problem in write_literal and print_literal lint suggestion (rust-lang#13990)

fix rust-lang#13959

The current implementation of the `write_literal` and `print_literal`
lint performs escaping for the second argument of `write!` ,`writeln!`,
`print!` and `println!` of the suggestion by first replacing `"` with
`\"`, and then replacing `\` with `\\`. Performing these replacements in
this order may lead to unnecessary backslashes being added if the
original code contains `"` (e.g. `"` -> `\\"`), potentially resulting in
a suggestion that causes the code to fail to compile.
In the issue mentioned above, it’s suggested to use raw strings as raw
strings, but implementing this would require an ad-hoc change to the
current implementation, so it has been deferred. (I'll implement this in
another PR)

changelog: [`write_literal`]: fix incorrect escaping of suggestions
changelog: [`print_literal`]: fix incorrect escaping of suggestions

Author: Centri3

clippy_lints/src/write.rs

@@ -522,7 +522,7 @@ fn check_literal(cx: &LateContext<'_>, format_args: &FormatArgs, name: &str) {
 
             let replacement = match (format_string_is_raw, replace_raw) {
                 (false, false) => Some(replacement),
-                (false, true) => Some(replacement.replace('"', "\\\"").replace('\\', "\\\\")),
+                (false, true) => Some(replacement.replace('\\', "\\\\").replace('"', "\\\"")),
                 (true, false) => match conservative_unescape(&replacement) {
                     Ok(unescaped) => Some(unescaped),
                     Err(UnescapeErr::Lint) => None,

tests/ui/print_literal.fixed

@@ -66,3 +66,17 @@ fn main() {
 
     println!("mixed: {{hello}} {world}");
 }
+
+fn issue_13959() {
+    println!("\"");
+    println!(
+        "
+        foo
+        \\
+        \\\\
+        \"
+        \\\"
+        bar
+"
+    );
+}

tests/ui/print_literal.rs

@@ -66,3 +66,18 @@ fn main() {
 
     println!("mixed: {} {world}", "{hello}");
 }
+
+fn issue_13959() {
+    println!("{}", r#"""#);
+    println!(
+        "{}",
+        r#"
+        foo
+        \
+        \\
+        "
+        \"
+        bar
+"#
+    );
+}

tests/ui/print_literal.stderr

@@ -192,5 +192,41 @@ LL -     println!("mixed: {} {world}", "{hello}");
 LL +     println!("mixed: {{hello}} {world}");
    |
 
-error: aborting due to 16 previous errors
+error: literal with an empty format string
+  --> tests/ui/print_literal.rs:71:20
+   |
+LL |     println!("{}", r#"""#);
+   |                    ^^^^^^
+   |
+help: try
+   |
+LL -     println!("{}", r#"""#);
+LL +     println!("\"");
+   |
+
+error: literal with an empty format string
+  --> tests/ui/print_literal.rs:74:9
+   |
+LL | /         r#"
+LL | |         foo
+LL | |         \
+LL | |         \\
+...  |
+LL | |         bar
+LL | | "#
+   | |__^
+   |
+help: try
+   |
+LL ~         "
+LL +         foo
+LL +         \\
+LL +         \\\\
+LL +         \"
+LL +         \\\"
+LL +         bar
+LL ~ "
+   |
+
+error: aborting due to 18 previous errors
 

tests/ui/write_literal.fixed

@@ -62,3 +62,19 @@ fn main() {
     writeln!(v, "hello {0} {1}, world {2}", 2, 3, 4);
     //~^ ERROR: literal with an empty format string
 }
+
+fn issue_13959() {
+    let mut v = Vec::new();
+    writeln!(v, "\"");
+    writeln!(
+        v,
+        "
+        foo
+        \\
+        \\\\
+        \"
+        \\\"
+        bar
+"
+    );
+}

tests/ui/write_literal.rs

@@ -62,3 +62,20 @@ fn main() {
     writeln!(v, "{0} {1} {2}, {3} {4}", "hello", 2, 3, "world", 4);
     //~^ ERROR: literal with an empty format string
 }
+
+fn issue_13959() {
+    let mut v = Vec::new();
+    writeln!(v, "{}", r#"""#);
+    writeln!(
+        v,
+        "{}",
+        r#"
+        foo
+        \
+        \\
+        "
+        \"
+        bar
+"#
+    );
+}

tests/ui/write_literal.stderr

@@ -144,5 +144,41 @@ LL -     writeln!(v, "{0} {1} {2}, {3} {4}", "hello", 2, 3, "world", 4);
 LL +     writeln!(v, "hello {0} {1}, world {2}", 2, 3, 4);
    |
 
-error: aborting due to 12 previous errors
+error: literal with an empty format string
+  --> tests/ui/write_literal.rs:68:23
+   |
+LL |     writeln!(v, "{}", r#"""#);
+   |                       ^^^^^^
+   |
+help: try
+   |
+LL -     writeln!(v, "{}", r#"""#);
+LL +     writeln!(v, "\"");
+   |
+
+error: literal with an empty format string
+  --> tests/ui/write_literal.rs:72:9
+   |
+LL | /         r#"
+LL | |         foo
+LL | |         \
+LL | |         \\
+...  |
+LL | |         bar
+LL | | "#
+   | |__^
+   |
+help: try
+   |
+LL ~         "
+LL +         foo
+LL +         \\
+LL +         \\\\
+LL +         \"
+LL +         \\\"
+LL +         bar
+LL ~ "
+   |
+
+error: aborting due to 14 previous errors