Rollup merge of #58629 - euclio:debug-empty-str, r=alexcrichton

rust-lldb: fix crash when printing empty string

Fixes #52185.

Re-enables the pretty-std debuginfo test and tweaks the test as necessary to get it to pass again. This reveals that lldb's formatting of enums is broken (#58492). I also removed the emoji from the test because I couldn't get the docker image's gdb to print the emoji, just octal escapes (https://github.com/rust-lang/rust/pull/53154/files#r208263904).

src/etc/lldb_rust_formatters.py

@@ -290,6 +290,8 @@ def render_element(i):
 
 
 def read_utf8_string(ptr_val, byte_count):
+    if byte_count == 0:
+        return '""'
     error = lldb.SBError()
     process = ptr_val.get_wrapped_value().GetProcess()
     data = process.ReadMemory(ptr_val.as_integer(), byte_count, error)

src/test/debuginfo/pretty-std.rs

@@ -1,6 +1,5 @@
 // ignore-windows failing on win32 bot
 // ignore-freebsd: gdb package too new
-// ignore-test // Test temporarily ignored due to debuginfo tests being disabled, see PR 47155
 // ignore-android: FIXME(#10381)
 // compile-flags:-g
 // min-gdb-version 7.7
@@ -23,45 +22,54 @@
 // gdb-check:$4 = "IAMA string!"
 
 // gdb-command: print some
-// gdb-check:$5 = Some = {8}
+// gdbg-check:$5 = Some = {8}
+// gdbr-check:$5 = core::option::Option<i16>::Some(8)
 
 // gdb-command: print none
 // gdbg-check:$6 = None
-// gdbr-check:$6 = core::option::Option::None
+// gdbr-check:$6 = core::option::Option<i64>::None
 
 // gdb-command: print os_string
-// gdb-check:$7 = "IAMA OS string 😃"
+// gdb-check:$7 = "IAMA OS string"
 
 // gdb-command: print some_string
-// gdb-check:$8 = Some = {"IAMA optional string!"}
+// gdbg-check:$8 = {RUST$ENCODED$ENUM$0$None = Some = {"IAMA optional string!"}}
+// gdbr-check:$8 = core::option::Option<alloc::string::String>::Some("IAMA optional string!")
 
-// gdb-command: set print length 5
+// gdb-command: set print elements 5
 // gdb-command: print some_string
-// gdb-check:$8 = Some = {"IAMA "...}
+// gdbg-check:$9 = {RUST$ENCODED$ENUM$0$None = Some = {"IAMA "...}}
+// gdbr-check:$9 = core::option::Option<alloc::string::String>::Some("IAMA "...)
 
+// gdb-command: print empty_str
+// gdb-check:$10 = ""
 
 // === LLDB TESTS ==================================================================================
 
 // lldb-command: run
 
-// lldb-command: print slice
-// lldb-check:[...]$0 = &[0, 1, 2, 3]
+// lldb-command: fr v slice
+// lldb-check:[...]slice = &[0, 1, 2, 3]
 
-// lldb-command: print vec
-// lldb-check:[...]$1 = vec![4, 5, 6, 7]
+// lldb-command: fr v vec
+// lldb-check:[...]vec = vec![4, 5, 6, 7]
 
-// lldb-command: print str_slice
-// lldb-check:[...]$2 = "IAMA string slice!"
+// lldb-command: fr v str_slice
+// lldb-check:[...]str_slice = "IAMA string slice!"
 
-// lldb-command: print string
-// lldb-check:[...]$3 = "IAMA string!"
+// lldb-command: fr v string
+// lldb-check:[...]string = "IAMA string!"
 
-// lldb-command: print some
-// lldb-check:[...]$4 = Some(8)
+// FIXME #58492
+// lldb-command: fr v some
+// lldb-check:[...]some = Option<i16> { }
 
-// lldb-command: print none
-// lldb-check:[...]$5 = None
+// FIXME #58492
+// lldb-command: fr v none
+// lldb-check:[...]none = Option<i64> { }
 
+// lldb-command: fr v empty_str
+// lldb-check:[...]empty_str = ""
 
 #![allow(unused_variables)]
 use std::ffi::OsString;
@@ -82,14 +90,16 @@ fn main() {
     let string = "IAMA string!".to_string();
 
     // OsString
-    let os_string = OsString::from("IAMA OS string \u{1F603}");
+    let os_string = OsString::from("IAMA OS string");
 
     // Option
     let some = Some(8i16);
     let none: Option<i64> = None;
 
     let some_string = Some("IAMA optional string!".to_owned());
 
+    let empty_str = "";
+
     zzz(); // #break
 }