Modifies the rendering of constant values in rustdoc.

[sladyn98]

Previously, non-literal expressions (like 50 + 50) would be printed
alongside their value as a comment (like = _; // 100i32). This approach
often resulted in confusing documentation, especially for complex expressions.

To improve clarity, this commit changes the rendering to display the evaluated
value of the expression directly (like = 100i32;) unless the constant is a
literal expression. The original expression is still included as a comment if it
doesn't match the evaluated value.

These changes aim to improve the readability and usefulness of constant value
documentation generated by rustdoc.

[rustbot]

r? @notriddle

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[sladyn98]

CC @GuillaumeGomez I thought of implementing this fix before migration to Askama

[GuillaumeGomez]

This sounds like a good improvement to me. However, this is a very complicated topic. So first let's hear from the last person who worked (a lot) on this. cc @fmease

[fmease]

Overall the changes look fine, thanks for tackling the FIXME!
However please address the nits and update the tests.

For context, I wrote this FIXME and it would also be fixed by #99688
which is currently blocked on an RFC that I need to write (but which
I didn't do yet since I'm no longer sure if it's the right direction for
rustdoc but that's another story).

Your changes seem to be a good middle ground in the meantime.

[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[sladyn98]

Closing this PR and opening a new one, I guess the fork on this one got corrupted and involved changes that are not currently related to this PR

[rust-log-analyzer]

The job x86_64-gnu-llvm-14 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [rustdoc] tests/rustdoc/const-value-display.rs stdout ----

error: htmldocck failed!
status: exit status: 1
command: "/usr/bin/python3" "/checkout/src/etc/htmldocck.py" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc/const-value-display" "/checkout/tests/rustdoc/const-value-display.rs"
stdout: none
4: @has check failed
4: @has check failed
 `XPATH PATTERN` did not match
 // @has - '//*[@class="rust item-decl"]//code' 'pub const HOUR_IN_SECONDS: u64 = _; // 3_600u64'
8: @has check failed
 `XPATH PATTERN` did not match
 // @has - '//*[@class="rust item-decl"]//code' 'pub const NEGATIVE: i64 = _; // -3_600i64'
Encountered 2 errors
------------------------------------------



---- [rustdoc] tests/rustdoc/show-const-contents.rs stdout ----

error: htmldocck failed!
status: exit status: 1
command: "/usr/bin/python3" "/checkout/src/etc/htmldocck.py" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc/show-const-contents" "/checkout/tests/rustdoc/show-const-contents.rs"
stdout: none
--- stderr -------------------------------
13: @!hasraw check failed
 `PATTERN` did not match
 // @!hasraw show_const_contents/constant.CONST_I32_HEX.html '; //'
24: @hasraw check failed
 `PATTERN` did not match
 // @hasraw show_const_contents/constant.CONST_CALC_I32.html '= _; // 43i32'
Build completed unsuccessfully in 0:13:18
31: @hasraw check failed
 `PATTERN` did not match
 // @hasraw show_const_contents/constant.CONST_I32_MAX.html '= i32::MAX; // 2_147_483_647i32'
50: @hasraw check failed
 `PATTERN` did not match
 // @hasraw show_const_contents/constant.PI.html '= 3.14159265358979323846264338327950288f32;'
54: @hasraw check failed
 `PATTERN` did not match
 // @hasraw show_const_contents/constant.MAX.html '= i32::MAX; // 2_147_483_647i32'
64: @hasraw check failed
 `PATTERN` did not match
 // @hasraw show_const_contents/constant.MIN.html '= i16::MIN; // -32_768i16'
Encountered 6 errors
------------------------------------------