Fix minor mis-accounting of column position in report.wordWrap (#449)

This PR also adds a test to exercise the corner case.

Author: mcy

experimental/report/testdata/no-snippets.yaml

@@ -36,7 +36,7 @@ diagnostics:
     level: LEVEL_REMARK
     in_file: foo.proto
     notes: 
-      - "this footer is very very very very very very very very very very very very very very very very very very long"
+      - "this footer is a very very very very very very very very very very very very very very very very very very very very very very long footer"
       - "this one is also long, and it's also supercalifragilistcexpialidocious, leading to a very early break"
     help:
       - "this help is very long (and triggers the same word-wrapping code path)"

experimental/report/testdata/no-snippets.yaml.color.txt

@@ -14,8 +14,9 @@
 
 ⟨b.cyn⟩remark: very long footers
 ⟨blu⟩ --> foo.proto
-  ⟨blu⟩ = ⟨b.cyn⟩note: ⟨reset⟩this footer is very very very very very very very very very very very
-           very very very very very very very long
+  ⟨blu⟩ = ⟨b.cyn⟩note: ⟨reset⟩this footer is a very very very very very very very very very very
+           very very very very very very very very very very very very long
+           footer
   ⟨blu⟩ = ⟨b.cyn⟩note: ⟨reset⟩this one is also long, and it's also
            supercalifragilistcexpialidocious, leading to a very early break
   ⟨blu⟩ = ⟨b.cyn⟩help: ⟨reset⟩this help is very long (and triggers the same word-wrapping code

experimental/report/testdata/no-snippets.yaml.fancy.txt

@@ -14,8 +14,9 @@ warning: file consists only of the byte `0xaa`
 
 remark: very long footers
  --> foo.proto
-   = note: this footer is very very very very very very very very very very very
-           very very very very very very very long
+   = note: this footer is a very very very very very very very very very very
+           very very very very very very very very very very very very long
+           footer
    = note: this one is also long, and it's also
            supercalifragilistcexpialidocious, leading to a very early break
    = help: this help is very long (and triggers the same word-wrapping code

experimental/report/width.go

@@ -48,28 +48,34 @@ func wordWrap(text string, width int) iter.Seq[string] {
 		// Split along lines first, since those are hard breaks we don't plan
 		// to change.
 		stringsx.Lines(text)(func(line string) bool {
-			line = strings.TrimSpace(line)
 			var nextIsSpace bool
 			var column, cursor int
 
 			stringsx.PartitionKey(line, unicode.IsSpace)(func(start int, chunk string) bool {
 				isSpace := nextIsSpace
 				nextIsSpace = !nextIsSpace
 
-				column = stringWidth(column, chunk, true, nil)
-				if column <= width {
+				if isSpace && column == 0 {
 					return true
 				}
 
-				line := line[cursor:start]
-				if !yield(strings.TrimSpace(line)) {
+				w := stringWidth(column, chunk, true, nil) - column
+				if column+w <= width {
+					column += w
+					return true
+				}
+
+				if !yield(strings.TrimSpace(line[cursor:start])) {
 					return false
 				}
-				cursor = start
+
 				if isSpace {
-					cursor += len(chunk)
+					cursor = start + len(chunk)
+					column = 0
+				} else {
+					cursor = start
+					column = w
 				}
-				column = 0
 				return true
 			})