rustdoc: improve diagnostics on raw doc fragments

1. rustdoc::bare_urls doesn't output
   invalid suggestions if source_span_for_markdown_range
   fails to find a span

2. source_span_for_markdown_range tries harder to
   return a span by applying an additional diagnostic

fixes https://github.com/rust-lang/rust/issues/135851

7 files changed, 99 insertions, 33 deletions

diff --git a/tests/rustdoc-ui/intra-doc/warning.stderr b/tests/rustdoc-ui/intra-doc/warning.stderr
index 3a06f1787e0..9b3f6f822d7 100644
--- a/tests/rustdoc-ui/intra-doc/warning.stderr
+++ b/tests/rustdoc-ui/intra-doc/warning.stderr
@@ -69,29 +69,19 @@ LL | bar [BarC] bar
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
 warning: unresolved link to `BarD`
-  --> $DIR/warning.rs:45:9
+  --> $DIR/warning.rs:45:20
    |
 LL | #[doc = "Foo\nbar [BarD] bar\nbaz"]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                    ^^^^ no item named `BarD` in scope
    |
-   = note: the link appears in this line:
-           
-           bar [BarD] bar
-                ^^^^
-   = note: no item named `BarD` in scope
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
 warning: unresolved link to `BarF`
-  --> $DIR/warning.rs:54:4
+  --> $DIR/warning.rs:54:15
    |
 LL | f!("Foo\nbar [BarF] bar\nbaz");
-   |    ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |               ^^^^ no item named `BarF` in scope
    |
-   = note: the link appears in this line:
-           
-           bar [BarF] bar
-                ^^^^
-   = note: no item named `BarF` in scope
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
    = note: this warning originates in the macro `f` (in Nightly builds, run with -Z macro-backtrace for more info)
 
@@ -112,29 +102,19 @@ LL |  * time to introduce a link [error]
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
 warning: unresolved link to `error`
-  --> $DIR/warning.rs:68:9
+  --> $DIR/warning.rs:68:23
    |
 LL | #[doc = "single line [error]"]
-   |         ^^^^^^^^^^^^^^^^^^^^^
+   |                       ^^^^^ no item named `error` in scope
    |
-   = note: the link appears in this line:
-           
-           single line [error]
-                        ^^^^^
-   = note: no item named `error` in scope
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
 warning: unresolved link to `error`
-  --> $DIR/warning.rs:71:9
+  --> $DIR/warning.rs:71:41
    |
 LL | #[doc = "single line with \"escaping\" [error]"]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                         ^^^^^ no item named `error` in scope
    |
-   = note: the link appears in this line:
-           
-           single line with "escaping" [error]
-                                        ^^^^^
-   = note: no item named `error` in scope
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
 warning: unresolved link to `error`
diff --git a/tests/rustdoc-ui/lints/bare-urls-limit.rs b/tests/rustdoc-ui/lints/bare-urls-limit.rs
new file mode 100644
index 00000000000..f64154b0496
--- /dev/null
+++ b/tests/rustdoc-ui/lints/bare-urls-limit.rs
@@ -0,0 +1,12 @@
+//@ check-fail
+
+#![deny(rustdoc::bare_urls)]
+
+// examples of bare urls that are beyond our ability to generate suggestions for
+
+// this falls through every heuristic in `source_span_for_markdown_range`,
+// and thus does not get any suggestion.
+#[doc = "good: <https://example.com/> \n\n"]
+//~^ ERROR this URL is not a hyperlink
+#[doc = "bad: https://example.com/"]
+pub fn duplicate_raw() {}
diff --git a/tests/rustdoc-ui/lints/bare-urls-limit.stderr b/tests/rustdoc-ui/lints/bare-urls-limit.stderr
new file mode 100644
index 00000000000..9573665cb13
--- /dev/null
+++ b/tests/rustdoc-ui/lints/bare-urls-limit.stderr
@@ -0,0 +1,18 @@
+error: this URL is not a hyperlink
+  --> $DIR/bare-urls-limit.rs:9:9
+   |
+LL |   #[doc = "good: <https://example.com/> \n\n"]
+   |  _________^
+LL | |
+LL | | #[doc = "bad: https://example.com/"]
+   | |___________________________________^
+   |
+   = note: bare URLs are not automatically turned into clickable links
+note: the lint level is defined here
+  --> $DIR/bare-urls-limit.rs:3:9
+   |
+LL | #![deny(rustdoc::bare_urls)]
+   |         ^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/rustdoc-ui/lints/bare-urls.fixed b/tests/rustdoc-ui/lints/bare-urls.fixed
index 7938d715199..a91573146b8 100644
--- a/tests/rustdoc-ui/lints/bare-urls.fixed
+++ b/tests/rustdoc-ui/lints/bare-urls.fixed
@@ -38,6 +38,16 @@
 //~^ ERROR this URL is not a hyperlink
 pub fn c() {}
 
+#[doc = "here's a thing: <https://example.com/>"]
+//~^ ERROR this URL is not a hyperlink
+pub fn f() {}
+
+/// <https://example.com/sugar>
+//~^ ERROR this URL is not a hyperlink
+#[doc = "<https://example.com/raw>"]
+//~^ ERROR this URL is not a hyperlink
+pub fn mixed() {}
+
 /// <https://somewhere.com>
 /// [a](http://a.com)
 /// [b]
diff --git a/tests/rustdoc-ui/lints/bare-urls.rs b/tests/rustdoc-ui/lints/bare-urls.rs
index 75f42b78ffb..5b008cdafa2 100644
--- a/tests/rustdoc-ui/lints/bare-urls.rs
+++ b/tests/rustdoc-ui/lints/bare-urls.rs
@@ -38,6 +38,16 @@
 //~^ ERROR this URL is not a hyperlink
 pub fn c() {}
 
+#[doc = "here's a thing: https://example.com/"]
+//~^ ERROR this URL is not a hyperlink
+pub fn f() {}
+
+/// https://example.com/sugar
+//~^ ERROR this URL is not a hyperlink
+#[doc = "https://example.com/raw"]
+//~^ ERROR this URL is not a hyperlink
+pub fn mixed() {}
+
 /// <https://somewhere.com>
 /// [a](http://a.com)
 /// [b]
diff --git a/tests/rustdoc-ui/lints/bare-urls.stderr b/tests/rustdoc-ui/lints/bare-urls.stderr
index ddfc387eaf6..e1108c7e7f8 100644
--- a/tests/rustdoc-ui/lints/bare-urls.stderr
+++ b/tests/rustdoc-ui/lints/bare-urls.stderr
@@ -207,5 +207,41 @@ help: use an automatic link instead
 LL | /// hey! <https://somewhere.com/a?hello=12&bye=11#xyz>
    |          +                                           +
 
-error: aborting due to 17 previous errors
+error: this URL is not a hyperlink
+  --> $DIR/bare-urls.rs:41:26
+   |
+LL | #[doc = "here's a thing: https://example.com/"]
+   |                          ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: bare URLs are not automatically turned into clickable links
+help: use an automatic link instead
+   |
+LL | #[doc = "here's a thing: <https://example.com/>"]
+   |                          +                    +
+
+error: this URL is not a hyperlink
+  --> $DIR/bare-urls.rs:45:5
+   |
+LL | /// https://example.com/sugar
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: bare URLs are not automatically turned into clickable links
+help: use an automatic link instead
+   |
+LL | /// <https://example.com/sugar>
+   |     +                         +
+
+error: this URL is not a hyperlink
+  --> $DIR/bare-urls.rs:47:10
+   |
+LL | #[doc = "https://example.com/raw"]
+   |          ^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: bare URLs are not automatically turned into clickable links
+help: use an automatic link instead
+   |
+LL | #[doc = "<https://example.com/raw>"]
+   |          +                       +
+
+error: aborting due to 20 previous errors
 
diff --git a/tests/rustdoc-ui/unescaped_backticks.stderr b/tests/rustdoc-ui/unescaped_backticks.stderr
index d93aaf5f3ca..1bcb88e108f 100644
--- a/tests/rustdoc-ui/unescaped_backticks.stderr
+++ b/tests/rustdoc-ui/unescaped_backticks.stderr
@@ -628,10 +628,10 @@ LL | /// or even to add a number `n` to 42 (`add(42, n)\`)!
    |                                                   +
 
 error: unescaped backtick
-  --> $DIR/unescaped_backticks.rs:108:9
+  --> $DIR/unescaped_backticks.rs:108:10
    |
 LL | #[doc = "`"]
-   |         ^^^
+   |          ^
    |
    = help: the opening or closing backtick of an inline code may be missing
    = help: if you meant to use a literal backtick, escape it
@@ -639,10 +639,10 @@ LL | #[doc = "`"]
            to this: \`
 
 error: unescaped backtick
-  --> $DIR/unescaped_backticks.rs:115:9
+  --> $DIR/unescaped_backticks.rs:115:26
    |
 LL | #[doc = concat!("\\", "`")]
-   |         ^^^^^^^^^^^^^^^^^^^^
+   |                          ^
    |
    = help: the opening backtick of an inline code may be missing
             change: \`