Auto merge of #124500 - VladimirMakaev:lldb-str-formatters, r=Mark-Simulacrum

lldb-formatters: Use StdSliceSyntheticProvider for &str

&str has associated summary provider which correctly displays string values in debugger, but while working on #124458 I've noticed that a &str inside an enum displays a blob of memory until a 0 is reached (as a c-string) which makes a very bizarre experience when debugging

However there is already StdSliceSyntheticProvider which we use for other slices. This PR enables the same synthetic provider to be used for &str, however the summary provider is still fixed to return the string value

I've added a test `debuginfo/strings-and-strs.rs` which prior to this PR would output the following in LLDB:
```
* thread #1, name = 'a', stop reason = breakpoint 1.1
    frame #0: 0x0000555555556383 a`strings_and_strs::main::h1d2b5f9227b8767d at strings-and-strs.rs:47:5
   44  	    let plain_str = "Hello";
   45  	    let str_in_struct = Foo { inner: "Hello" };
   46  	    let str_in_tuple = ("Hello", "World");
-> 47  	    zzz(); // #break
   48  	}
   49
   50  	fn zzz() {
(lldb) frame var
(alloc::string::String) plain_string = "Hello" {
  vec = size=5 {
    [0] = 'H'
    [1] = 'e'
    [2] = 'l'
    [3] = 'l'
    [4] = 'o'
  }
}
(&str) plain_str = "Hello" {
  data_ptr = 0x0000555555557263 "HelloWorld\U00000001gdb_load_rust_pretty_printers.py"
  length = 5
}
(strings_and_strs::Foo) str_in_struct = {
  inner = "Hello" {
    data_ptr = 0x0000555555557263 "HelloWorld\U00000001gdb_load_rust_pretty_printers.py"
    length = 5
  }
}
((&str, &str)) str_in_tuple = {
  0 = "Hello" {
    data_ptr = 0x0000555555557263 "HelloWorld\U00000001gdb_load_rust_pretty_printers.py"
    length = 5
  }
  1 = "World" {
    data_ptr = 0x0000555555557268 "World\U00000001gdb_load_rust_pretty_printers.py"
    length = 5
  }
}
```
After this PR it would look the following way:

```
* thread #1, name = 'a', stop reason = breakpoint 1.1
    frame #0: 0x0000555555556383 a`strings_and_strs::main::h1d2b5f9227b8767d at strings-and-strs.rs:47:5
   44  	    let plain_str = "Hello";
   45  	    let str_in_struct = Foo { inner: "Hello" };
   46  	    let str_in_tuple = ("Hello", "World");
-> 47  	    zzz(); // #break
   48  	}
   49
   50  	fn zzz() {
(lldb) frame var
(alloc::string::String) plain_string = "Hello" {
  vec = size=5 {
    [0] = 'H'
    [1] = 'e'
    [2] = 'l'
    [3] = 'l'
    [4] = 'o'
  }
}
(&str) plain_str = "Hello" {
  [0] = 'H'
  [1] = 'e'
  [2] = 'l'
  [3] = 'l'
  [4] = 'o'
}
(strings_and_strs::Foo) str_in_struct = {
  inner = "Hello" {
    [0] = 'H'
    [1] = 'e'
    [2] = 'l'
    [3] = 'l'
    [4] = 'o'
  }
}
((&str, &str)) str_in_tuple = {
  0 = "Hello" {
    [0] = 'H'
    [1] = 'e'
    [2] = 'l'
    [3] = 'l'
    [4] = 'o'
  }
  1 = "World" {
    [0] = 'W'
    [1] = 'o'
    [2] = 'r'
    [3] = 'l'
    [4] = 'd'
  }
}
```

Author: bors

library/std/src/sys/pal/unix/alloc.rs

@@ -59,10 +59,9 @@ unsafe impl GlobalAlloc for System {
 }
 
 cfg_if::cfg_if! {
-    // We use posix_memalign wherever possible, but not all targets have that function.
+    // We use posix_memalign wherever possible, but some targets have very incomplete POSIX coverage
+    // so we need a fallback for those.
     if #[cfg(any(
-        target_os = "redox",
-        target_os = "espidf",
         target_os = "horizon",
         target_os = "vita",
     ))] {
@@ -74,12 +73,11 @@ cfg_if::cfg_if! {
         #[inline]
         unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
             let mut out = ptr::null_mut();
-            // We prefer posix_memalign over aligned_malloc since with aligned_malloc,
-            // implementations are making almost arbitrary choices for which alignments are
-            // "supported", making it hard to use. For instance, some implementations require the
-            // size to be a multiple of the alignment (wasi emmalloc), while others require the
-            // alignment to be at least the pointer size (Illumos, macOS) -- which may or may not be
-            // standards-compliant, but that does not help us.
+            // We prefer posix_memalign over aligned_malloc since it is more widely available, and
+            // since with aligned_malloc, implementations are making almost arbitrary choices for
+            // which alignments are "supported", making it hard to use. For instance, some
+            // implementations require the size to be a multiple of the alignment (wasi emmalloc),
+            // while others require the alignment to be at least the pointer size (Illumos, macOS).
             // posix_memalign only has one, clear requirement: that the alignment be a multiple of
             // `sizeof(void*)`. Since these are all powers of 2, we can just use max.
             let align = layout.align().max(crate::mem::size_of::<usize>());

src/etc/lldb_lookup.py

@@ -92,7 +92,7 @@ def synthetic_lookup(valobj, dict):
         return StdVecSyntheticProvider(valobj, dict)
     if rust_type == RustType.STD_VEC_DEQUE:
         return StdVecDequeSyntheticProvider(valobj, dict)
-    if rust_type == RustType.STD_SLICE:
+    if rust_type == RustType.STD_SLICE or rust_type == RustType.STD_STR:
         return StdSliceSyntheticProvider(valobj, dict)
 
     if rust_type == RustType.STD_HASH_MAP:

src/etc/lldb_providers.py

@@ -159,6 +159,9 @@ def StdStrSummaryProvider(valobj, dict):
     # logger = Logger.Logger()
     # logger >> "[StdStrSummaryProvider] for " + str(valobj.GetName())
 
+    # the code below assumes non-synthetic value, this makes sure the assumption holds
+    valobj = valobj.GetNonSyntheticValue()
+
     length = valobj.GetChildMemberWithName("length").GetValueAsUnsigned()
     if length == 0:
         return '""'

tests/debuginfo/empty-string.rs

@@ -23,7 +23,7 @@
 // lldb-check:[...] empty_string = "" { vec = size=0 }
 
 // lldb-command:fr v empty_str
-// lldb-check:[...] empty_str = "" { data_ptr = [...] length = 0 }
+// lldb-check:[...] empty_str = ""
 
 fn main() {
     let empty_string = String::new();

tests/debuginfo/pretty-slices.rs

@@ -27,10 +27,10 @@
 // lldb-check:(&mut [i32]) mut_slice = size=4 { [0] = 2 [1] = 3 [2] = 5 [3] = 7 }
 
 // lldb-command:v str_slice
-// lldb-check:(&str) str_slice = "string slice" { data_ptr = [...] length = 12 }
+// lldb-check:(&str) str_slice = "string slice" { [0] = 's' [1] = 't' [2] = 'r' [3] = 'i' [4] = 'n' [5] = 'g' [6] = ' ' [7] = 's' [8] = 'l' [9] = 'i' [10] = 'c' [11] = 'e' }
 
 // lldb-command:v mut_str_slice
-// lldb-check:(&mut str) mut_str_slice = "mutable string slice" { data_ptr = [...] length = 20 }
+// lldb-check:(&mut str) mut_str_slice = "mutable string slice" { [0] = 'm' [1] = 'u' [2] = 't' [3] = 'a' [4] = 'b' [5] = 'l' [6] = 'e' [7] = ' ' [8] = 's' [9] = 't' [10] = 'r' [11] = 'i' [12] = 'n' [13] = 'g' [14] = ' ' [15] = 's' [16] = 'l' [17] = 'i' [18] = 'c' [19] = 'e' }
 
 fn b() {}
 

tests/debuginfo/strings-and-strs.rs

@@ -0,0 +1,63 @@
+//@ min-gdb-version: 14.0
+//@ min-lldb-version: 1800
+
+//@ compile-flags:-g
+
+// === GDB TESTS ===================================================================================
+// gdb-command:run
+
+// gdb-command:print plain_string
+// gdbr-check:$1 = alloc::string::String {vec: alloc::vec::Vec<u8, alloc::alloc::Global> {buf: alloc::raw_vec::RawVec<u8, alloc::alloc::Global> {ptr: core::ptr::unique::Unique<u8> {pointer: core::ptr::non_null::NonNull<u8> {pointer: 0x55555555ab80}, _marker: core::marker::PhantomData<u8>}, cap: alloc::raw_vec::Cap (5), alloc: alloc::alloc::Global}, len: 5}}
+
+// gdb-command:print plain_str
+// gdbr-check:$2 = "Hello"
+
+// gdb-command:print str_in_struct
+// gdbr-check:$3 = strings_and_strs::Foo {inner: "Hello"}
+
+// gdb-command:print str_in_tuple
+// gdbr-check:$4 = ("Hello", "World")
+
+// gdb-command:print str_in_rc
+// gdbr-check:$5 = alloc::rc::Rc<&str, alloc::alloc::Global> {ptr: core::ptr::non_null::NonNull<alloc::rc::RcBox<&str>> {pointer: 0x55555555aae0}, phantom: core::marker::PhantomData<alloc::rc::RcBox<&str>>, alloc: alloc::alloc::Global}
+
+
+// === LLDB TESTS ==================================================================================
+// lldb-command:run
+// lldb-command:v plain_string
+// lldbg-check:(alloc::string::String) plain_string = "Hello" { vec = size=5 { [0] = 'H' [1] = 'e' [2] = 'l' [3] = 'l' [4] = 'o' } }
+
+// lldb-command:v plain_str
+// lldbg-check:(&str) plain_str = "Hello" { [0] = 'H' [1] = 'e' [2] = 'l' [3] = 'l' [4] = 'o' }
+
+// lldb-command:v str_in_struct
+// lldbg-check:((&str, &str)) str_in_tuple = { 0 = "Hello" { [0] = 'H' [1] = 'e' [2] = 'l' [3] = 'l' [4] = 'o' } 1 = "World" { [0] = 'W' [1] = 'o' [2] = 'r' [3] = 'l' [4] = 'd' } }
+
+// lldb-command:v str_in_tuple
+// lldbg-check:((&str, &str)) str_in_tuple = { 0 = "Hello" { [0] = 'H' [1] = 'e' [2] = 'l' [3] = 'l' [4] = 'o' } 1 = "World" { [0] = 'W' [1] = 'o' [2] = 'r' [3] = 'l' [4] = 'd' } }
+
+// lldb-command:v str_in_rc
+// lldbg-check:(alloc::rc::Rc<&str, alloc::alloc::Global>) str_in_rc = strong=1, weak=0 { value = "Hello" { [0] = 'H' [1] = 'e' [2] = 'l' [3] = 'l' [4] = 'o' } }
+
+
+#![allow(unused_variables)]
+#![feature(omit_gdb_pretty_printer_section)]
+#![omit_gdb_pretty_printer_section]
+
+pub struct Foo<'a> {
+    inner: &'a str,
+}
+
+fn main() {
+    let plain_string = String::from("Hello");
+    let plain_str = "Hello";
+    let str_in_struct = Foo { inner: "Hello" };
+    let str_in_tuple = ("Hello", "World");
+
+    let str_in_rc = std::rc::Rc::new("Hello");
+    zzz(); // #break
+}
+
+fn zzz() {
+    ()
+}