Change:
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the problem is probably line 8 of the suggestion? !
claim
Minimized a bit more: The issue occurs because we compute a wrong span for the args . Instead of this: it spans the entire distance from the end of in the first line to the end of in the next line: The reasons for this is that we compute the span starting from the end of the variant path segment ( in this case) to end of the args (the right angle bracket of of ). Normally it works, but leads to the above miscalculation when the variant and the args reside in different macros or expansions as in the present case. The offending source code doing the span computation is this:

Discussion:
use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS; use rustc_span::edit_distance::find_best_match_for_name; use rustc_span::symbol::{kw, Ident, Symbol}; <del> use rustc_span::{sym, Span, DUMMY_SP}; </del> <ins> use rustc_span::{sym, BytePos, Span, DUMMY_SP}; </ins> use rustc_target::spec::abi; use rustc_trait_selection::traits::wf::object_region_bounds; use rustc_trait_selection::traits::{self, NormalizeExt, ObligationCtxt};

return; }; // Get the span of the generics args *including* the leading `::`. <del> let args_span = assoc_segment.ident.span.shrink_to_hi().to(args.span_ext); </del> <ins> // We do so by stretching args.span_ext to the left by 2. Earlier // it was done based on the end of assoc segment but that sometimes // led to impossible spans and caused issues like #116473 let args_span = args.span_ext.with_lo(args.span_ext.lo() - BytePos(2)); </ins> if tcx.generics_of(adt_def.did()).count() == 0 { // FIXME(estebank): we could also verify that the arguments being // work for the `enum`, instead of just looking if it takes *any*.

<ins> // Regression test for ICE #116473. // The ICE occurs when arguments are specified on an enum variant // (which is illegal) and the variant and its preceding path are // located at different places such as in different macros or // different expansions of the same macro (i.e. when the macro // calls itself recursively) enum Enum<T1, T2> {  VariantA { _v1: T1, _v2: T2 }, VariantB } type EnumUnit = Enum<(), ()>; // Recursive macro call using a tt metavariable for variant macro_rules! recursive_tt { () => (recursive_tt!(VariantB)); ($variant:tt) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); //~^ ERROR type arguments are not allowed on this type //~| ERROR mismatched types } // Recursive macro call using an ident metavariable for variant // (the behaviour is different for tt and ident) macro_rules! recursive_ident { () => (recursive_ident!(VariantB)); ($variant:ident) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); //~^ ERROR type arguments are not allowed on this type //~| ERROR mismatched types } // Mested macro calls (i.e. one calling another) using a tt // metavariable for variant macro_rules! nested1_tt { () => (nested2_tt!(VariantB)); } macro_rules! nested2_tt { ($variant:tt) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); //~^ ERROR type arguments are not allowed on this type //~| ERROR mismatched types } // Mested macro calls using an ident metavariable for variant // (the behaviour is different for tt and ident) macro_rules! nested1_ident { () => (nested2_ident!(VariantB)); } macro_rules! nested2_ident { ($variant:ident) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); //~^ ERROR type arguments are not allowed on this type //~| ERROR mismatched types } // Mested macro calls when args are passed as metavariable // instead of the enum variant macro_rules! nested1_tt_args_in_first_macro { () => (nested2_tt_args_in_first_macro!(i32, u32)); } macro_rules! nested2_tt_args_in_first_macro { ($arg1:tt, $arg2:tt) => (if let EnumUnit::VariantB::<$arg1, $arg2> {} //~^ ERROR type arguments are not allowed on this type //~| ERROR mismatched types = 5 { true } else { false }); } // Mested macro calls when args are passed as metavariable // instead of the enum variant macro_rules! nested1_ident_args_in_first_macro { () => (nested2_ident_args_in_first_macro!(i32, u32)); } macro_rules! nested2_ident_args_in_first_macro { ($arg1:ident, $arg2:ident) => (if let EnumUnit::VariantB::<$arg1, $arg2> {} //~^ ERROR type arguments are not allowed on this type //~| ERROR mismatched types = 5 { true } else { false }); } fn main() { // Macro cases recursive_tt!(); recursive_ident!(); nested1_tt!(); nested1_ident!(); nested1_tt_args_in_first_macro!(); nested1_ident_args_in_first_macro!(); // Regular, non-macro case if let EnumUnit::VariantB::<i32, u32> {} = 5 { true } else { false }; //~^ ERROR type arguments are not allowed on this type //~| ERROR mismatched types } </ins>

<ins> error[E0109]: type arguments are not allowed on this type --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:15:51 | LL |     ($variant:tt) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); |                                        --------   ^^^  ^^^ type argument not allowed |                                        | |                                        not allowed on this type ... LL |     recursive_tt!(); |     --------------- |     | |     in this macro invocation |     in this macro invocation | = note: enum variants can't have type parameters = note: this error originates in the macro `recursive_tt` (in Nightly builds, run with -Z macro-backtrace for more info) help: you might have meant to specify type parameters on enum `Enum` | LL -     ($variant:tt) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); LL +     ($variant:tt) => (if let EnumUnit::<i32, u32>::$variant {} = 5 { true } else { false }); | error[E0308]: mismatched types --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:15:30 | LL |     ($variant:tt) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `{integer}` |                              | |                              expected integer, found `Enum<(), ()>` ... LL |     recursive_tt!(); |     --------------- in this macro invocation | = note: expected type `{integer}` found enum `Enum<(), ()>` = note: this error originates in the macro `recursive_tt` (in Nightly builds, run with -Z macro-backtrace for more info) error[E0109]: type arguments are not allowed on this type --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:25:54 | LL |     () => (recursive_ident!(VariantB)); |                             -------- not allowed on this type LL |     ($variant:ident) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); |                                                      ^^^  ^^^ type argument not allowed ... LL |     recursive_ident!(); |     ------------------ |     | |     in this macro invocation |     in this macro invocation | = note: enum variants can't have type parameters = note: this error originates in the macro `recursive_ident` (in Nightly builds, run with -Z macro-backtrace for more info) help: you might have meant to specify type parameters on enum `Enum` | LL -     ($variant:ident) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); LL +     ($variant:ident) => (if let EnumUnit::<i32, u32>::$variant {} = 5 { true } else { false }); | error[E0308]: mismatched types --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:25:33 | LL |     ($variant:ident) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `{integer}` |                                 | |                                 expected integer, found `Enum<(), ()>` ... LL |     recursive_ident!(); |     ------------------ in this macro invocation | = note: expected type `{integer}` found enum `Enum<(), ()>` = note: this error originates in the macro `recursive_ident` (in Nightly builds, run with -Z macro-backtrace for more info) error[E0109]: type arguments are not allowed on this type --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:38:51 | LL |     ($variant:tt) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); |                                        --------   ^^^  ^^^ type argument not allowed |                                        | |                                        not allowed on this type ... LL |     nested1_tt!(); |     ------------- |     | |     in this macro invocation |     in this macro invocation | = note: enum variants can't have type parameters = note: this error originates in the macro `nested2_tt` which comes from the expansion of the macro `nested1_tt` (in Nightly builds, run with -Z macro-backtrace for more info) help: you might have meant to specify type parameters on enum `Enum` | LL -     ($variant:tt) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); LL +     ($variant:tt) => (if let EnumUnit::<i32, u32>::$variant {} = 5 { true } else { false }); | error[E0308]: mismatched types --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:38:30 | LL |     ($variant:tt) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `{integer}` |                              | |                              expected integer, found `Enum<(), ()>` ... LL |     nested1_tt!(); |     ------------- in this macro invocation | = note: expected type `{integer}` found enum `Enum<(), ()>` = note: this error originates in the macro `nested2_tt` which comes from the expansion of the macro `nested1_tt` (in Nightly builds, run with -Z macro-backtrace for more info) error[E0109]: type arguments are not allowed on this type --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:51:54 | LL |     () => (nested2_ident!(VariantB)); |                           -------- not allowed on this type ... LL |     ($variant:ident) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); |                                                      ^^^  ^^^ type argument not allowed ... LL |     nested1_ident!(); |     ---------------- |     | |     in this macro invocation |     in this macro invocation | = note: enum variants can't have type parameters = note: this error originates in the macro `nested2_ident` which comes from the expansion of the macro `nested1_ident` (in Nightly builds, run with -Z macro-backtrace for more info) help: you might have meant to specify type parameters on enum `Enum` | LL -     ($variant:ident) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); LL +     ($variant:ident) => (if let EnumUnit::<i32, u32>::$variant {} = 5 { true } else { false }); | error[E0308]: mismatched types --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:51:33 | LL |     ($variant:ident) => (if let EnumUnit::$variant::<i32, u32> {} = 5 { true } else { false }); |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `{integer}` |                                 | |                                 expected integer, found `Enum<(), ()>` ... LL |     nested1_ident!(); |     ---------------- in this macro invocation | = note: expected type `{integer}` found enum `Enum<(), ()>` = note: this error originates in the macro `nested2_ident` which comes from the expansion of the macro `nested1_ident` (in Nightly builds, run with -Z macro-backtrace for more info) error[E0109]: type arguments are not allowed on this type --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:64:58 | LL |     ($arg1:tt, $arg2:tt) => (if let EnumUnit::VariantB::<$arg1, $arg2> {} |                                               --------   ^^^^^  ^^^^^ type argument not allowed |                                               | |                                               not allowed on this type ... LL |     nested1_tt_args_in_first_macro!(); |     --------------------------------- |     | |     in this macro invocation |     in this macro invocation | = note: enum variants can't have type parameters = note: this error originates in the macro `nested1_tt_args_in_first_macro` (in Nightly builds, run with -Z macro-backtrace for more info) help: you might have meant to specify type parameters on enum `Enum` | LL -     ($arg1:tt, $arg2:tt) => (if let EnumUnit::VariantB::<$arg1, $arg2> {} LL +     ($arg1:tt, $arg2:tt) => (if let EnumUnit::<$arg1, $arg2>::VariantB {} | error[E0308]: mismatched types --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:64:37 | LL |     ($arg1:tt, $arg2:tt) => (if let EnumUnit::VariantB::<$arg1, $arg2> {} |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected integer, found `Enum<(), ()>` ... LL |             = 5 { true } else { false }); |               - this expression has type `{integer}` ... LL |     nested1_tt_args_in_first_macro!(); |     --------------------------------- in this macro invocation | = note: expected type `{integer}` found enum `Enum<(), ()>` = note: this error originates in the macro `nested2_tt_args_in_first_macro` which comes from the expansion of the macro `nested1_tt_args_in_first_macro` (in Nightly builds, run with -Z macro-backtrace for more info) error[E0109]: type arguments are not allowed on this type --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:77:64 | LL |     ($arg1:ident, $arg2:ident) => (if let EnumUnit::VariantB::<$arg1, $arg2> {} |                                                     --------   ^^^^^  ^^^^^ type argument not allowed |                                                     | |                                                     not allowed on this type ... LL |     nested1_ident_args_in_first_macro!(); |     ------------------------------------ |     | |     in this macro invocation |     in this macro invocation | = note: enum variants can't have type parameters = note: this error originates in the macro `nested2_ident_args_in_first_macro` which comes from the expansion of the macro `nested1_ident_args_in_first_macro` (in Nightly builds, run with -Z macro-backtrace for more info) help: you might have meant to specify type parameters on enum `Enum` | LL -     ($arg1:ident, $arg2:ident) => (if let EnumUnit::VariantB::<$arg1, $arg2> {} LL +     ($arg1:ident, $arg2:ident) => (if let EnumUnit::<$arg1, $arg2>::VariantB {} | error[E0308]: mismatched types --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:77:43 | LL |     ($arg1:ident, $arg2:ident) => (if let EnumUnit::VariantB::<$arg1, $arg2> {} |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected integer, found `Enum<(), ()>` ... LL |         = 5 { true } else { false }); |           - this expression has type `{integer}` ... LL |     nested1_ident_args_in_first_macro!(); |     ------------------------------------ in this macro invocation | = note: expected type `{integer}` found enum `Enum<(), ()>` = note: this error originates in the macro `nested2_ident_args_in_first_macro` which comes from the expansion of the macro `nested1_ident_args_in_first_macro` (in Nightly builds, run with -Z macro-backtrace for more info) error[E0109]: type arguments are not allowed on this type --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:93:33 | LL |     if let EnumUnit::VariantB::<i32, u32> {} = 5 { true } else { false }; |                      --------   ^^^  ^^^ type argument not allowed |                      | |                      not allowed on this type | = note: enum variants can't have type parameters help: you might have meant to specify type parameters on enum `Enum` | LL -     if let EnumUnit::VariantB::<i32, u32> {} = 5 { true } else { false }; LL +     if let EnumUnit::<i32, u32>::VariantB {} = 5 { true } else { false }; | error[E0308]: mismatched types --> $DIR/issue-116473-ice-wrong-span-variant-args.rs:93:12 | LL |     if let EnumUnit::VariantB::<i32, u32> {} = 5 { true } else { false }; |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `{integer}` |            | |            expected integer, found `Enum<(), ()>` | = note: expected type `{integer}` found enum `Enum<(), ()>` error: aborting due to 14 previous errors Some errors have detailed explanations: E0109, E0308. For more information about an error, try `rustc --explain E0109`. </ins>