Draw vertical lines in compiler error messages with multiline annotations correctly when non-1space unicode characters are to the left

For this we use the correct calculation of the 'left' identation

src/librustc_errors/emitter.rs

@@ -835,7 +835,7 @@ impl EmitterWriter {
             return vec![];
         }
 
-        // Write the colunmn separator.
+        // Write the column separator.
         //
         // After this we will have:
         //
@@ -906,7 +906,7 @@ impl EmitterWriter {
         //   |  __________
         //   | |    |
         //   | |
-        // 3 |
+        // 3 | |
         // 4 | | }
         //   | |_
         for &(pos, annotation) in &annotations_position {
@@ -920,7 +920,7 @@ impl EmitterWriter {
             if pos > 1 && (annotation.has_label() || annotation.takes_space()) {
                 for p in line_offset + 1..=line_offset + pos {
                     buffer.putc(p,
-                                code_offset + annotation.start_col - margin.computed_left,
+                                (code_offset + annotation.start_col).saturating_sub(left),
                                 '|',
                                 style);
                 }

src/test/ui/terminal-width/non-1-width-unicode-multiline-label.rs

@@ -0,0 +1,7 @@
+// ignore-tidy-linelength
+
+fn main() {
+    let unicode_is_fun = "؁‱ஹ௸௵꧄.ဪ꧅⸻𒈙𒐫﷽𒌄𒈟𒍼𒁎𒀱𒌧𒅃 𒈓𒍙𒊎𒄡𒅌𒁏𒀰𒐪𒐩𒈙𒐫𪚥";
+    let _ = "ༀ༁༂༃༄༅༆༇༈༉༊་༌།༎༏༐༑༒༓༔༕༖༗༘༙༚༛༜༝༞༟༠༡༢༣༤༥༦༧༨༩༪༫༬༭༮༯༰༱༲༳༴༵༶༷༸༹༺༻༼༽༾༿ཀཁགགྷངཅཆཇ཈ཉཊཋཌཌྷཎཏཐདདྷནཔཕབབྷམཙཚཛཛྷཝཞཟའཡརལཤཥསཧཨཀྵཪཫཬ཭཮཯཰ཱཱཱིིུུྲྀཷླྀཹེཻོཽཾཿ྄ཱྀྀྂྃ྅྆྇ྈྉྊྋྌྍྎྏྐྑྒྒྷྔྕྖྗ྘ྙྚྛྜྜྷྞྟྠྡྡྷྣྤྥྦྦྷྨྩྪྫྫྷྭྮྯྰྱྲླྴྵྶྷྸྐྵྺྻྼ྽྾྿࿀࿁࿂࿃࿄࿅࿆࿇࿈࿉࿊࿋࿌࿍࿎࿏࿐࿑࿒࿓࿔࿕࿖࿗࿘࿙࿚"; let _a = unicode_is_fun + " really fun!";
+    //~^ ERROR binary operation `+` cannot be applied to type `&str`
+}

src/test/ui/terminal-width/non-1-width-unicode-multiline-label.stderr

@@ -0,0 +1,17 @@
+error[E0369]: binary operation `+` cannot be applied to type `&str`
+  --> $DIR/non-1-width-unicode-multiline-label.rs:5:260
+   |
+LL | ...ཽཾཿ྄ཱྀྀྂྃ྅྆྇ྈྉྊྋྌྍྎྏྐྑྒྒྷྔྕྖྗ྘ྙྚྛྜྜྷྞྟྠྡྡྷྣྤྥྦྦྷྨྩྪྫྫྷྭྮྯྰྱྲླྴྵྶྷྸྐྵྺྻྼ྽྾྿࿀࿁࿂࿃࿄࿅࿆࿇...࿋࿌࿍࿎࿏࿐࿑࿒࿓࿔࿕࿖࿗࿘࿙࿚"; let _a = unicode_is_fun + " really fun!";
+   |                                                  -------------- ^ -------------- &str
+   |                                                  |              |
+   |                                                  |              `+` cannot be used to concatenate two `&str` strings
+   |                                                  &str
+   |
+help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   |
+LL |     let _ = "ༀ༁༂༃༄༅༆༇༈༉༊་༌།༎༏༐༑༒༓༔༕༖༗༘༙༚༛༜༝༞༟༠༡༢༣༤༥༦༧༨༩༪༫༬༭༮༯༰༱༲༳༴༵༶༷༸༹༺༻༼༽༾༿ཀཁགགྷངཅཆཇ཈ཉཊཋཌཌྷཎཏཐདདྷནཔཕབབྷམཙཚཛཛྷཝཞཟའཡརལཤཥསཧཨཀྵཪཫཬ཭཮཯཰ཱཱཱིིུུྲྀཷླྀཹེཻོཽཾཿ྄ཱྀྀྂྃ྅྆྇ྈྉྊྋྌྍྎྏྐྑྒྒྷྔྕྖྗ྘ྙྚྛྜྜྷྞྟྠྡྡྷྣྤྥྦྦྷྨྩྪྫྫྷྭྮྯྰྱྲླྴྵྶྷྸྐྵྺྻྼ྽྾྿࿀࿁࿂࿃࿄࿅࿆࿇࿈࿉࿊࿋࿌࿍࿎࿏࿐࿑࿒࿓࿔࿕࿖࿗࿘࿙࿚"; let _a = unicode_is_fun.to_owned() + " really fun!";
+   |                                                                                                                                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0369`.

src/test/ui/terminal-width/non-whitespace-trimming-unicode.stderr

@@ -3,7 +3,7 @@ error[E0308]: mismatched types
    |
 LL | ...♭♮♯♰♱♲♳♴♵♶♷♸♹♺♻♼♽♾♿⚀⚁⚂⚃⚄⚅⚆⚈⚉4"; let _: () = 42;  let _: &str = "🦀☀☁☂☃☄★☆☇☈☉☊☋☌☍☎☏☐☑☒☓  ☖☗☘☙☚☛☜☝☞☟☠☡☢☣☤☥☦☧☨☩☪☫☬☭☮☯☰☱☲☳☴☵☶☷☸☹☺☻☼☽☾☿♀♁♂♃♄...
    |                                            --   ^^ expected `()`, found integer
-   |                                                     |
+   |                                            |
    |                                            expected due to this
 
 error: aborting due to previous error