print: accurately track (fractional) line width, and raise the max wi…

…dth back to 120. (#37)

*Originally found/fixed during the #33/#34/#35/#36 series of
pretty-printing PRs.*

Before this PR, we were treating all text the same, regardless of style,
but this PR introduces the concept of "fractional columns" (integer
multiples of `0.1ch`, because our `font-size`s are always integer
multiples of `0.1em`).

The result is much more accurate, and so far appears to perfectly match
browser behavior (i.e. the transition of `MAX_LINE_WIDTH` from `N-1` to
`N`, where multi-line layout gets replaced with single-line layout,
results in a line that "tightly fits" in a `max-width: Nch` container,
with no spurious gaps or overflows).

Note however that the increased accuracy makes the layout favor HTML
over plaintext (and we don't have a plaintext-vs-HTML "simultaneous
layout", nor a way to hint what the output of pretty layout will be used
for), so the plaintext output may feel more inconsistent as a result
(but its aesthetics are of dubious value anyway).

CHANGELOG.md

@@ -40,6 +40,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   example (which only dumped plaintext, not HTML) with a more useful `spv-lower-print` one
 
 ### Fixed 🩹
+- [PR#37](https://github.com/EmbarkStudios/spirt/pull/37) fixed pretty-printing layout
+  accuracy regarding line widths (by tracking `font-size`-aware "fractional columns"),
+  and raised the maximum line width back up to `120` columns
 - [PR#27](https://github.com/EmbarkStudios/spirt/pull/27) fixed some pretty-printing issues
   in the initial `Attr::Diagnostics` implementation (`BUG` paths and `/* ... */` indentation)
 

src/print/mod.rs

@@ -490,7 +490,7 @@ impl Visit for AllCxInterned {
 }
 
 // FIXME(eddyb) make max line width configurable.
-const MAX_LINE_WIDTH: usize = 100;
+const MAX_LINE_WIDTH: usize = 120;
 
 impl Plan<'_> {
     #[allow(rustdoc::private_intra_doc_links)]

src/print/multiversion.rs

@@ -121,7 +121,19 @@ impl Versions<pretty::FragmentPostLayout> {
     }
     SCOPE>tbody>tr>td {
         vertical-align: top;
+    }
+    SCOPE>tbody>tr>td>pre {
         max-width: MAX_LINE_WIDTHch;
+
+        overflow-x: auto;
+
+        /* HACK(eddyb) this shouldn't be needed but `visible` will turn into
+           `auto` because `overflow-x` is `auto` (for cursed browser reasons),
+           and some table cells are always assumed to need vertical scroll,
+           e.g. because they have `<sub>` elements on the last line (which don't
+           contribute to the surrounding bounding box, due to `line-height: 0`)
+         */
+        overflow-y: hidden;
     }
 </style>
         "