Improve handling of tmp variable name conflicts

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1325,13 +1325,17 @@ impl<'a> Parser<'a> {
         kind: IncDecRecovery,
         (pre_span, post_span): (Span, Span),
     ) {
+        let mut msg = format!("use `{}= 1` instead", kind.op.chr());
+        if base_src.trim() == "tmp" {
+            msg.push_str(" (rename `tmp` so it doesn't conflict with your variable)");
+        }
         err.multipart_suggestion(
-            &format!("use `{}= 1` instead", kind.op.chr()),
+            &msg,
             vec![
                 (pre_span, "{ let tmp = ".to_string()),
                 (post_span, format!("; {} {}= 1; tmp }}", base_src, kind.op.chr())),
             ],
-            Applicability::MachineApplicable,
+            Applicability::HasPlaceholders,
         );
     }
 

src/test/ui/parser/increment-autofix.rs

@@ -14,6 +14,20 @@ fn post_while() {
     }
 }
 
+fn post_regular_tmp() {
+    let mut tmp = 0;
+    tmp++; //~ ERROR Rust has no postfix increment operator
+    println!("{}", tmp);
+}
+
+fn post_while_tmp() {
+    let mut tmp = 0;
+    while tmp++ < 5 {
+        //~^ ERROR Rust has no postfix increment operator
+        println!("{}", tmp);
+    }
+}
+
 fn pre_regular() {
     let mut i = 0;
     ++i; //~ ERROR Rust has no prefix increment operator
@@ -31,6 +45,8 @@ fn pre_while() {
 fn main() {
     post_regular();
     post_while();
+    post_regular_tmp();
+    post_while_tmp();
     pre_regular();
     pre_while();
 }

src/test/ui/parser/increment-autofix.stderr

@@ -30,8 +30,40 @@ LL -     while i++ < 5 {
 LL +     while i += 1 < 5 {
    | 
 
+error: Rust has no postfix increment operator
+  --> $DIR/increment-autofix.rs:19:8
+   |
+LL |     tmp++;
+   |        ^^ not a valid postfix operator
+   |
+help: use `+= 1` instead (rename `tmp` so it doesn't conflict with your variable)
+   |
+LL |     { let tmp = tmp; tmp += 1; tmp };
+   |     +++++++++++    ~~~~~~~~~~~~~~~~~
+help: or, if you don't need to use it as an expression, change it to this
+   |
+LL -     tmp++;
+LL +     tmp += 1;
+   | 
+
+error: Rust has no postfix increment operator
+  --> $DIR/increment-autofix.rs:25:14
+   |
+LL |     while tmp++ < 5 {
+   |              ^^ not a valid postfix operator
+   |
+help: use `+= 1` instead (rename `tmp` so it doesn't conflict with your variable)
+   |
+LL |     while { let tmp = tmp; tmp += 1; tmp } < 5 {
+   |           +++++++++++    ~~~~~~~~~~~~~~~~~
+help: or, if you don't need to use it as an expression, change it to this
+   |
+LL -     while tmp++ < 5 {
+LL +     while tmp += 1 < 5 {
+   | 
+
 error: Rust has no prefix increment operator
-  --> $DIR/increment-autofix.rs:19:5
+  --> $DIR/increment-autofix.rs:33:5
    |
 LL |     ++i;
    |     ^^ not a valid prefix operator
@@ -43,7 +75,7 @@ LL +     i += 1;
    | 
 
 error: Rust has no prefix increment operator
-  --> $DIR/increment-autofix.rs:25:11
+  --> $DIR/increment-autofix.rs:39:11
    |
 LL |     while ++i < 5 {
    |           ^^ not a valid prefix operator
@@ -53,5 +85,5 @@ help: use `+= 1` instead
 LL |     while { i += 1; i } < 5 {
    |           ~   +++++++++
 
-error: aborting due to 4 previous errors
+error: aborting due to 6 previous errors
 

src/test/ui/parser/increment-notfixed.rs

@@ -13,6 +13,16 @@ fn post_field() {
     println!("{}", foo.bar.qux);
 }
 
+fn post_field_tmp() {
+    struct S {
+        tmp: i32
+    }
+    let s = S { tmp: 0 };
+    s.tmp++;
+    //~^ ERROR Rust has no postfix increment operator
+    println!("{}", s.tmp);
+}
+
 fn pre_field() {
     let foo = Foo { bar: Bar { qux: 0 } };
     ++foo.bar.qux;
@@ -22,5 +32,6 @@ fn pre_field() {
 
 fn main() {
     post_field();
+    post_field_tmp();
     pre_field();
 }

src/test/ui/parser/increment-notfixed.stderr

@@ -14,8 +14,24 @@ LL -     foo.bar.qux++;
 LL +     foo.bar.qux += 1;
    | 
 
+error: Rust has no postfix increment operator
+  --> $DIR/increment-notfixed.rs:21:10
+   |
+LL |     s.tmp++;
+   |          ^^ not a valid postfix operator
+   |
+help: use `+= 1` instead
+   |
+LL |     { let tmp = s.tmp; s.tmp += 1; tmp };
+   |     +++++++++++      ~~~~~~~~~~~~~~~~~~~
+help: or, if you don't need to use it as an expression, change it to this
+   |
+LL -     s.tmp++;
+LL +     s.tmp += 1;
+   | 
+
 error: Rust has no prefix increment operator
-  --> $DIR/increment-notfixed.rs:18:5
+  --> $DIR/increment-notfixed.rs:28:5
    |
 LL |     ++foo.bar.qux;
    |     ^^ not a valid prefix operator
@@ -26,5 +42,5 @@ LL -     ++foo.bar.qux;
 LL +     foo.bar.qux += 1;
    | 
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors