Auto merge of rust-lang#76843 - kornelski:longtypetofile, r=ecstatic-morse

Let user see the full type of type-length limit error

Seeing the full type of the error is sometimes essential to diagnosing the problem, but the type itself is too long to be displayed in the terminal in a useful fashion. This change solves this dilemma by writing the full offending type name to a file, and displays this filename as a note.

> note: the full type name been written to '$TEST_BUILD_DIR/issues/issue-22638/issue-22638.long-type.txt'

Closes rust-lang#76777

Author: bors

compiler/rustc_mir/src/monomorphize/collector.rs

@@ -197,6 +197,7 @@ use rustc_session::config::EntryFnType;
 use rustc_span::source_map::{dummy_spanned, respan, Span, Spanned, DUMMY_SP};
 use smallvec::SmallVec;
 use std::iter;
+use std::path::PathBuf;
 
 #[derive(PartialEq)]
 pub enum MonoItemCollectionMode {
@@ -420,27 +421,38 @@ fn record_accesses<'a, 'tcx: 'a>(
     inlining_map.lock_mut().record_accesses(caller, &accesses);
 }
 
-// Shrinks string by keeping prefix and suffix of given sizes.
-fn shrink(s: String, before: usize, after: usize) -> String {
-    // An iterator of all byte positions including the end of the string.
-    let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
-
-    let shrunk = format!(
-        "{before}...{after}",
-        before = &s[..positions().nth(before).unwrap_or(s.len())],
-        after = &s[positions().rev().nth(after).unwrap_or(0)..],
-    );
+/// Format instance name that is already known to be too long for rustc.
+/// Show only the first and last 32 characters to avoid blasting
+/// the user's terminal with thousands of lines of type-name.
+///
+/// If the type name is longer than before+after, it will be written to a file.
+fn shrunk_instance_name(
+    tcx: TyCtxt<'tcx>,
+    instance: &Instance<'tcx>,
+    before: usize,
+    after: usize,
+) -> (String, Option<PathBuf>) {
+    let s = instance.to_string();
 
     // Only use the shrunk version if it's really shorter.
     // This also avoids the case where before and after slices overlap.
-    if shrunk.len() < s.len() { shrunk } else { s }
-}
+    if s.chars().nth(before + after + 1).is_some() {
+        // An iterator of all byte positions including the end of the string.
+        let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
+
+        let shrunk = format!(
+            "{before}...{after}",
+            before = &s[..positions().nth(before).unwrap_or(s.len())],
+            after = &s[positions().rev().nth(after).unwrap_or(0)..],
+        );
+
+        let path = tcx.output_filenames(LOCAL_CRATE).temp_path_ext("long-type.txt", None);
+        let written_to_path = std::fs::write(&path, s).ok().map(|_| path);
 
-// Format instance name that is already known to be too long for rustc.
-// Show only the first and last 32 characters to avoid blasting
-// the user's terminal with thousands of lines of type-name.
-fn shrunk_instance_name(instance: &Instance<'tcx>) -> String {
-    shrink(instance.to_string(), 32, 32)
+        (shrunk, written_to_path)
+    } else {
+        (s, None)
+    }
 }
 
 fn check_recursion_limit<'tcx>(
@@ -465,15 +477,16 @@ fn check_recursion_limit<'tcx>(
     // more than the recursion limit is assumed to be causing an
     // infinite expansion.
     if !tcx.sess.recursion_limit().value_within_limit(adjusted_recursion_depth) {
-        let error = format!(
-            "reached the recursion limit while instantiating `{}`",
-            shrunk_instance_name(&instance),
-        );
+        let (shrunk, written_to_path) = shrunk_instance_name(tcx, &instance, 32, 32);
+        let error = format!("reached the recursion limit while instantiating `{}`", shrunk);
         let mut err = tcx.sess.struct_span_fatal(span, &error);
         err.span_note(
             tcx.def_span(def_id),
             &format!("`{}` defined here", tcx.def_path_str(def_id)),
         );
+        if let Some(path) = written_to_path {
+            err.note(&format!("the full type name has been written to '{}'", path.display()));
+        }
         err.emit();
         FatalError.raise();
     }
@@ -502,12 +515,13 @@ fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
     //
     // Bail out in these cases to avoid that bad user experience.
     if !tcx.sess.type_length_limit().value_within_limit(type_length) {
-        let msg = format!(
-            "reached the type-length limit while instantiating `{}`",
-            shrunk_instance_name(&instance),
-        );
+        let (shrunk, written_to_path) = shrunk_instance_name(tcx, &instance, 32, 32);
+        let msg = format!("reached the type-length limit while instantiating `{}`", shrunk);
         let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
-        diag.note(&format!(
+        if let Some(path) = written_to_path {
+            diag.note(&format!("the full type name has been written to '{}'", path.display()));
+        }
+        diag.help(&format!(
             "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
             type_length
         ));

src/test/ui/infinite/infinite-instantiation.rs

@@ -1,4 +1,5 @@
 // build-fail
+// normalize-stderr-test: ".nll/" -> "/"
 
 trait ToOpt: Sized {
     fn to_option(&self) -> Option<Self>;

src/test/ui/infinite/infinite-instantiation.stderr

@@ -1,14 +1,15 @@
 error: reached the recursion limit while instantiating `function::<Option<Option<Option<...>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
-  --> $DIR/infinite-instantiation.rs:21:9
+  --> $DIR/infinite-instantiation.rs:22:9
    |
 LL |         function(counter - 1, t.to_option());
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `function` defined here
-  --> $DIR/infinite-instantiation.rs:19:1
+  --> $DIR/infinite-instantiation.rs:20:1
    |
 LL | fn function<T:ToOpt + Clone>(counter: usize, t: T) {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: the full type name has been written to '$TEST_BUILD_DIR/infinite/infinite-instantiation/infinite-instantiation.long-type.txt'
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-22638.rs

@@ -1,5 +1,6 @@
 // build-fail
 // normalize-stderr-test: "<\[closure@.+`" -> "$$CLOSURE`"
+// normalize-stderr-test: ".nll/" -> "/"
 
 #![allow(unused)]
 

src/test/ui/issues/issue-22638.stderr

@@ -1,14 +1,15 @@
 error: reached the recursion limit while instantiating `A::matches::$CLOSURE`
-  --> $DIR/issue-22638.rs:55:9
+  --> $DIR/issue-22638.rs:56:9
    |
 LL |         a.matches(f)
    |         ^^^^^^^^^^^^
    |
 note: `A::matches` defined here
-  --> $DIR/issue-22638.rs:14:5
+  --> $DIR/issue-22638.rs:15:5
    |
 LL |     pub fn matches<F: Fn()>(&self, f: &F) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: the full type name has been written to '$TEST_BUILD_DIR/issues/issue-22638/issue-22638.long-type.txt'
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-37311-type-length-limit/issue-37311.rs

@@ -1,4 +1,5 @@
 // build-fail
+// normalize-stderr-test: ".nll/" -> "/"
 
 trait Mirror {
     type Image;

src/test/ui/issues/issue-37311-type-length-limit/issue-37311.stderr

@@ -1,14 +1,15 @@
 error: reached the recursion limit while instantiating `<(&(&(&(&(&(&(&(&(&(&(&(&(&(&(&(.....), ...), ...) as Foo>::recurse`
-  --> $DIR/issue-37311.rs:16:9
+  --> $DIR/issue-37311.rs:17:9
    |
 LL |         (self, self).recurse();
    |         ^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `<T as Foo>::recurse` defined here
-  --> $DIR/issue-37311.rs:15:5
+  --> $DIR/issue-37311.rs:16:5
    |
 LL |     fn recurse(&self) {
    |     ^^^^^^^^^^^^^^^^^
+   = note: the full type name has been written to '$TEST_BUILD_DIR/issues/issue-37311-type-length-limit/issue-37311/issue-37311.long-type.txt'
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-67552.rs

@@ -1,4 +1,5 @@
 // build-fail
+// normalize-stderr-test: ".nll/" -> "/"
 
 fn main() {
     rec(Empty);

src/test/ui/issues/issue-67552.stderr

@@ -1,16 +1,17 @@
 error: reached the recursion limit while instantiating `rec::<&mut &mut &mut &mut &mut &... &mut &mut &mut &mut &mut Empty>`
-  --> $DIR/issue-67552.rs:27:9
+  --> $DIR/issue-67552.rs:28:9
    |
 LL |         rec(identity(&mut it))
    |         ^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `rec` defined here
-  --> $DIR/issue-67552.rs:20:1
+  --> $DIR/issue-67552.rs:21:1
    |
 LL | / fn rec<T>(mut it: T)
 LL | | where
 LL | |     T: Iterator,
    | |________________^
+   = note: the full type name has been written to '$TEST_BUILD_DIR/issues/issue-67552/issue-67552.long-type.txt'
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-8727.rs

@@ -2,6 +2,7 @@
 // recursions.
 
 // build-fail
+// normalize-stderr-test: ".nll/" -> "/"
 
 fn generic<T>() { //~ WARN function cannot return without recursing
     generic::<Option<T>>();

src/test/ui/issues/issue-8727.stderr

@@ -1,5 +1,5 @@
 warning: function cannot return without recursing
-  --> $DIR/issue-8727.rs:6:1
+  --> $DIR/issue-8727.rs:7:1
    |
 LL | fn generic<T>() {
    | ^^^^^^^^^^^^^^^ cannot return without recursing
@@ -10,16 +10,17 @@ LL |     generic::<Option<T>>();
    = help: a `loop` may express intention better if this is on purpose
 
 error: reached the recursion limit while instantiating `generic::<Option<Option<Option<O...>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
-  --> $DIR/issue-8727.rs:7:5
+  --> $DIR/issue-8727.rs:8:5
    |
 LL |     generic::<Option<T>>();
    |     ^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `generic` defined here
-  --> $DIR/issue-8727.rs:6:1
+  --> $DIR/issue-8727.rs:7:1
    |
 LL | fn generic<T>() {
    | ^^^^^^^^^^^^^^^
+   = note: the full type name has been written to '$TEST_BUILD_DIR/issues/issue-8727/issue-8727.long-type.txt'
 
 error: aborting due to previous error; 1 warning emitted
 

src/test/ui/recursion/issue-38591-non-regular-dropck-recursion.rs

@@ -2,7 +2,9 @@
 // no free regions or type parameters.
 // Codegen however, has to error for the infinitely many `drop_in_place`
 // functions it has been asked to create.
+
 // build-fail
+// normalize-stderr-test: ".nll/" -> "/"
 
 struct S<T> {
     t: T,

src/test/ui/recursion/issue-38591-non-regular-dropck-recursion.stderr

@@ -21,6 +21,7 @@ LL | |     // SAFETY: see comment above
 LL | |     unsafe { drop_in_place(to_drop) }
 LL | | }
    | |_^
+   = note: the full type name has been written to '$TEST_BUILD_DIR/recursion/issue-38591-non-regular-dropck-recursion/issue-38591-non-regular-dropck-recursion.long-type.txt'
 
 error: aborting due to previous error
 

src/test/ui/recursion/recursion.rs

@@ -1,5 +1,6 @@
 // build-fail
 // compile-flags:-C overflow-checks=off
+// normalize-stderr-test: ".nll/" -> "/"
 
 enum Nil {NilValue}
 struct Cons<T> {head:isize, tail:T}

src/test/ui/recursion/recursion.stderr

@@ -1,14 +1,15 @@
 error: reached the recursion limit while instantiating `test::<Cons<Cons<Cons<Cons<Cons<...>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
-  --> $DIR/recursion.rs:17:11
+  --> $DIR/recursion.rs:18:11
    |
 LL |     _ => {test (n-1, i+1, Cons {head:2*i+1, tail:first}, Cons{head:i*i, tail:second})}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `test` defined here
-  --> $DIR/recursion.rs:15:1
+  --> $DIR/recursion.rs:16:1
    |
 LL | fn test<T:Dot> (n:isize, i:isize, first:T, second:T) ->isize {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: the full type name has been written to '$TEST_BUILD_DIR/recursion/recursion/recursion.long-type.txt'
 
 error: aborting due to previous error
 

src/test/ui/type_length_limit.rs

@@ -1,5 +1,6 @@
 // build-fail
 // error-pattern: reached the type-length limit while instantiating
+// normalize-stderr-test: ".nll/" -> "/"
 
 // Test that the type length limit can be changed.
 

src/test/ui/type_length_limit.stderr

@@ -4,7 +4,8 @@ error: reached the type-length limit while instantiating `std::mem::drop::<Optio
 LL | pub fn drop<T>(_x: T) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: consider adding a `#![type_length_limit="8"]` attribute to your crate
+   = note: the full type name has been written to '$TEST_BUILD_DIR/type_length_limit/type_length_limit.long-type.txt'
+   = help: consider adding a `#![type_length_limit="8"]` attribute to your crate
 
 error: aborting due to previous error