From c4eeaabde241decdfaa1fbd9babb9ef98d74f1da Mon Sep 17 00:00:00 2001
From: Dennis Korpel <dkorpel@gmail.com>
Date: Sun, 5 Jan 2025 21:31:09 +0100
Subject: [PATCH] Fix -verrors=context handling of tabs

---
 compiler/src/dmd/errors.d                     | 33 ++++++++++++++++---
 .../fail_compilation/fail_pretty_errors.d     | 18 ++++++----
 2 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/compiler/src/dmd/errors.d b/compiler/src/dmd/errors.d
index 793e0ca3f2c..ce8f86bfc3c 100644
--- a/compiler/src/dmd/errors.d
+++ b/compiler/src/dmd/errors.d
@@ -744,19 +744,42 @@ private void verrorPrint(const(char)* format, va_list ap, ref ErrorInfo info)
                     continue;
                 if (loc.charnum < line.length)
                 {
-                    fprintf(stderr, "%.*s\n", cast(int)line.length, line.ptr);
+                    enum tabWidth = 4;
                     // The number of column bytes and the number of display columns
                     // occupied by a character are not the same for non-ASCII charaters.
                     // https://issues.dlang.org/show_bug.cgi?id=21849
-                    size_t col = 0;
-                    while (col < loc.charnum - 1)
+                    size_t index = 0;
+                    size_t column = 0;
+                    size_t caretColumn = 0;
+                    while (index < line.length)
                     {
                         import dmd.root.utf : utf_decodeChar;
                         dchar u;
-                        const msg = utf_decodeChar(line, col, u);
+                        const start = index;
+                        const msg = utf_decodeChar(line, index, u);
                         assert(msg is null, msg);
-                        fputc(' ', stderr);
+                        if (u == '\t')
+                        {
+                            // How many spaces until column is the next multiple of tabWidth
+                            const equivalentSpaces = tabWidth - (column % tabWidth);
+                            foreach (i; 0 .. equivalentSpaces)
+                                fputc(' ', stderr);
+                            column += equivalentSpaces;
+                        }
+                        else
+                        {
+                            fprintf(stderr, "%.*s", cast(int) (index - start), &line[start]);
+                            column++;
+                        }
+                        if (index < loc.charnum)
+                            caretColumn = column;
+
                     }
+                    fputc('\n', stderr);
+
+                    foreach (i; 0 .. caretColumn)
+                        fputc(' ', stderr);
+
                     fputc('^', stderr);
                     fputc('\n', stderr);
                 }
diff --git a/compiler/test/fail_compilation/fail_pretty_errors.d b/compiler/test/fail_compilation/fail_pretty_errors.d
index e9533c04c69..2016a501751 100644
--- a/compiler/test/fail_compilation/fail_pretty_errors.d
+++ b/compiler/test/fail_compilation/fail_pretty_errors.d
@@ -2,20 +2,23 @@
 REQUIRED_ARGS: -verrors=context
 TEST_OUTPUT:
 ---
-fail_compilation/fail_pretty_errors.d(24): Error: undefined identifier `a`
+fail_compilation/fail_pretty_errors.d(27): Error: undefined identifier `a`
     a = 1;
     ^
-fail_compilation/fail_pretty_errors.d-mixin-29(29): Error: undefined identifier `b`
-fail_compilation/fail_pretty_errors.d(34): Error: cannot implicitly convert expression `5` of type `int` to `string`
+fail_compilation/fail_pretty_errors.d-mixin-32(32): Error: undefined identifier `b`
+fail_compilation/fail_pretty_errors.d(37): Error: cannot implicitly convert expression `5` of type `int` to `string`
     string x = 5;
                ^
-fail_compilation/fail_pretty_errors.d(39): Error: mixin `fail_pretty_errors.testMixin2.mixinTemplate!()` error instantiating
+fail_compilation/fail_pretty_errors.d(42): Error: mixin `fail_pretty_errors.testMixin2.mixinTemplate!()` error instantiating
     mixin mixinTemplate;
     ^
-fail_compilation/fail_pretty_errors.d(45): Error: invalid array operation `"" + ""` (possible missing [])
+fail_compilation/fail_pretty_errors.d(48): Error: invalid array operation `"" + ""` (possible missing [])
     auto x = ""+"";
              ^
-fail_compilation/fail_pretty_errors.d(45):        did you mean to concatenate (`"" ~ ""`) instead ?
+fail_compilation/fail_pretty_errors.d(48):        did you mean to concatenate (`"" ~ ""`) instead ?
+fail_compilation/fail_pretty_errors.d(51): Error: cannot implicitly convert expression `1111` of type `int` to `byte`
+        byte ɑ =    1111;
+                    ^
 ---
 */
 
@@ -43,4 +46,7 @@ void f()
 {
     // check supplemental error doesn't show context
     auto x = ""+"";
+
+    // Check correct spacing with the presence of unicode characters and tabs
+	 	byte ɑ = 	1111;
 }