Rollup merge of #87715 - bhgomes:long-explanation-E0625, r=GuillaumeGomez

Add long error explanation for E0625

For #61137.

2 files changed, 29 insertions, 1 deletions

diff --git a/compiler/rustc_error_codes/src/error_codes.rs b/compiler/rustc_error_codes/src/error_codes.rs
index 65999ba707c..719c2c6768b 100644
--- a/compiler/rustc_error_codes/src/error_codes.rs
+++ b/compiler/rustc_error_codes/src/error_codes.rs
@@ -359,6 +359,7 @@ E0621: include_str!("./error_codes/E0621.md"),
 E0622: include_str!("./error_codes/E0622.md"),
 E0623: include_str!("./error_codes/E0623.md"),
 E0624: include_str!("./error_codes/E0624.md"),
+E0625: include_str!("./error_codes/E0625.md"),
 E0626: include_str!("./error_codes/E0626.md"),
 E0627: include_str!("./error_codes/E0627.md"),
 E0628: include_str!("./error_codes/E0628.md"),
@@ -622,7 +623,6 @@ E0783: include_str!("./error_codes/E0783.md"),
 //  E0611, // merged into E0616
 //  E0612, // merged into E0609
 //  E0613, // Removed (merged with E0609)
-    E0625, // thread-local statics cannot be accessed at compile-time
 //  E0629, // missing 'feature' (rustc_const_unstable)
 //  E0630, // rustc_const_unstable attribute must be paired with stable/unstable
            // attribute
diff --git a/compiler/rustc_error_codes/src/error_codes/E0625.md b/compiler/rustc_error_codes/src/error_codes/E0625.md
new file mode 100644
index 00000000000..7db857723cc
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0625.md
@@ -0,0 +1,28 @@
+A compile-time const variable is referring to a thread-local static variable.
+
+Erroneous code example:
+
+```compile_fail,E0625
+#![feature(thread_local)]
+
+#[thread_local]
+static X: usize = 12;
+
+const Y: usize = 2 * X;
+```
+
+Static and const variables can refer to other const variables but a const
+variable cannot refer to a thread-local static variable. In this example,
+`Y` cannot refer to `X`. To fix this, the value can be extracted as a const
+and then used:
+
+```
+#![feature(thread_local)]
+
+const C: usize = 12;
+
+#[thread_local]
+static X: usize = C;
+
+const Y: usize = 2 * C;
+```