Add typo suggestion for a misspelt Cargo environment variable

compiler/rustc_builtin_macros/messages.ftl

@@ -156,6 +156,7 @@ builtin_macros_duplicate_macro_attribute = duplicated attribute
 
 builtin_macros_env_not_defined = environment variable `{$var}` not defined at compile time
     .cargo = Cargo sets build script variables at run time. Use `std::env::var({$var_expr})` instead
+    .cargo_typo = there is a similar Cargo environment variable: `{$suggested_var}`
     .custom = use `std::env::var({$var_expr})` to read the variable at run time
 
 builtin_macros_env_not_unicode = environment variable `{$var}` is not a valid Unicode string

compiler/rustc_builtin_macros/src/env.rs

@@ -10,6 +10,7 @@ use rustc_ast::token::{self, LitKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{ExprKind, GenericArg, Mutability};
 use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
+use rustc_span::edit_distance::edit_distance;
 use rustc_span::{Ident, Span, Symbol, kw, sym};
 use thin_vec::thin_vec;
 
@@ -144,6 +145,12 @@ pub(crate) fn expand_env<'cx>(
                     if let Some(msg_from_user) = custom_msg {
                         cx.dcx()
                             .emit_err(errors::EnvNotDefinedWithUserMessage { span, msg_from_user })
+                    } else if let Some(suggested_var) = find_similar_cargo_var(var.as_str()) {
+                        cx.dcx().emit_err(errors::EnvNotDefined::CargoEnvVarTypo {
+                            span,
+                            var: *symbol,
+                            suggested_var: Symbol::intern(suggested_var),
+                        })
                     } else if is_cargo_env_var(var.as_str()) {
                         cx.dcx().emit_err(errors::EnvNotDefined::CargoEnvVar {
                             span,
@@ -176,3 +183,49 @@ fn is_cargo_env_var(var: &str) -> bool {
         || var.starts_with("DEP_")
         || matches!(var, "OUT_DIR" | "OPT_LEVEL" | "PROFILE" | "HOST" | "TARGET")
 }
+
+const KNOWN_CARGO_VARS: &[&str] = &[
+    // List of known Cargo environment variables that are set for crates (not build scripts, OUT_DIR etc).
+    // See: https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates
+    "CARGO_PKG_VERSION",
+    "CARGO_PKG_VERSION_MAJOR",
+    "CARGO_PKG_VERSION_MINOR",
+    "CARGO_PKG_VERSION_PATCH",
+    "CARGO_PKG_VERSION_PRE",
+    "CARGO_PKG_AUTHORS",
+    "CARGO_PKG_NAME",
+    "CARGO_PKG_DESCRIPTION",
+    "CARGO_PKG_HOMEPAGE",
+    "CARGO_PKG_REPOSITORY",
+    "CARGO_PKG_LICENSE",
+    "CARGO_PKG_LICENSE_FILE",
+    "CARGO_PKG_RUST_VERSION",
+    "CARGO_PKG_README",
+    "CARGO_MANIFEST_DIR",
+    "CARGO_MANIFEST_PATH",
+    "CARGO_CRATE_NAME",
+    "CARGO_BIN_NAME",
+    "CARGO_PRIMARY_PACKAGE",
+];
+
+fn find_similar_cargo_var(var: &str) -> Option<&'static str> {
+    if !var.starts_with("CARGO_") {
+        return None;
+    }
+
+    let lookup_len = var.chars().count();
+    let max_dist = std::cmp::max(lookup_len, 3) / 3;
+    let mut best_match = None;
+    let mut best_distance = usize::MAX;
+
+    for &known_var in KNOWN_CARGO_VARS {
+        if let Some(distance) = edit_distance(var, known_var, max_dist) {
+            if distance < best_distance {
+                best_distance = distance;
+                best_match = Some(known_var);
+            }
+        }
+    }
+
+    best_match
+}

compiler/rustc_builtin_macros/src/errors.rs

@@ -535,6 +535,14 @@ pub(crate) enum EnvNotDefined<'a> {
         var_expr: &'a rustc_ast::Expr,
     },
     #[diag(builtin_macros_env_not_defined)]
+    #[help(builtin_macros_cargo_typo)]
+    CargoEnvVarTypo {
+        #[primary_span]
+        span: Span,
+        var: Symbol,
+        suggested_var: Symbol,
+    },
+    #[diag(builtin_macros_env_not_defined)]
     #[help(builtin_macros_custom)]
     CustomEnvVar {
         #[primary_span]

tests/ui/env-macro/env-cargo-var-typo-issue-148439.rs

@@ -0,0 +1,50 @@
+//@ edition: 2021
+
+// Regression test for issue #148439
+// Ensure that when using misspelled Cargo environment variables in env!(),
+
+fn test_cargo_package_version() {
+    let _ = env!("CARGO_PACKAGE_VERSION");
+    //~^ ERROR environment variable `CARGO_PACKAGE_VERSION` not defined at compile time
+    //~| HELP there is a similar Cargo environment variable: `CARGO_PKG_VERSION`
+}
+
+fn test_cargo_package_name() {
+    let _ = env!("CARGO_PACKAGE_NAME");
+    //~^ ERROR environment variable `CARGO_PACKAGE_NAME` not defined at compile time
+    //~| HELP there is a similar Cargo environment variable: `CARGO_PKG_NAME`
+}
+
+fn test_cargo_package_authors() {
+    let _ = env!("CARGO_PACKAGE_AUTHORS");
+    //~^ ERROR environment variable `CARGO_PACKAGE_AUTHORS` not defined at compile time
+    //~| HELP there is a similar Cargo environment variable: `CARGO_PKG_AUTHORS`
+}
+
+fn test_cargo_manifest_directory() {
+    let _ = env!("CARGO_MANIFEST_DIRECTORY");
+    //~^ ERROR environment variable `CARGO_MANIFEST_DIRECTORY` not defined at compile time
+    //~| HELP there is a similar Cargo environment variable: `CARGO_MANIFEST_DIR`
+}
+
+fn test_cargo_pkg_version_typo() {
+    let _ = env!("CARGO_PKG_VERSIO");
+    //~^ ERROR environment variable `CARGO_PKG_VERSIO` not defined at compile time
+    //~| HELP there is a similar Cargo environment variable: `CARGO_PKG_VERSION`
+}
+
+fn test_non_cargo_var() {
+    // Non-Cargo variable should get different help message
+    let _ = env!("MY_CUSTOM_VAR");
+    //~^ ERROR environment variable `MY_CUSTOM_VAR` not defined at compile time
+    //~| HELP use `std::env::var("MY_CUSTOM_VAR")` to read the variable at run time
+}
+
+fn test_cargo_unknown_var() {
+    // Cargo-prefixed but not similar to any known variable
+    let _ = env!("CARGO_SOMETHING_TOTALLY_UNKNOWN");
+    //~^ ERROR environment variable `CARGO_SOMETHING_TOTALLY_UNKNOWN` not defined at compile time
+    //~| HELP Cargo sets build script variables at run time. Use `std::env::var("CARGO_SOMETHING_TOTALLY_UNKNOWN")` instead
+}
+
+fn main() {}

tests/ui/env-macro/env-cargo-var-typo-issue-148439.stderr

@@ -0,0 +1,58 @@
+error: environment variable `CARGO_PACKAGE_VERSION` not defined at compile time
+  --> $DIR/env-cargo-var-typo-issue-148439.rs:7:13
+   |
+LL |     let _ = env!("CARGO_PACKAGE_VERSION");
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: there is a similar Cargo environment variable: `CARGO_PKG_VERSION`
+
+error: environment variable `CARGO_PACKAGE_NAME` not defined at compile time
+  --> $DIR/env-cargo-var-typo-issue-148439.rs:13:13
+   |
+LL |     let _ = env!("CARGO_PACKAGE_NAME");
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: there is a similar Cargo environment variable: `CARGO_PKG_NAME`
+
+error: environment variable `CARGO_PACKAGE_AUTHORS` not defined at compile time
+  --> $DIR/env-cargo-var-typo-issue-148439.rs:19:13
+   |
+LL |     let _ = env!("CARGO_PACKAGE_AUTHORS");
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: there is a similar Cargo environment variable: `CARGO_PKG_AUTHORS`
+
+error: environment variable `CARGO_MANIFEST_DIRECTORY` not defined at compile time
+  --> $DIR/env-cargo-var-typo-issue-148439.rs:25:13
+   |
+LL |     let _ = env!("CARGO_MANIFEST_DIRECTORY");
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: there is a similar Cargo environment variable: `CARGO_MANIFEST_DIR`
+
+error: environment variable `CARGO_PKG_VERSIO` not defined at compile time
+  --> $DIR/env-cargo-var-typo-issue-148439.rs:31:13
+   |
+LL |     let _ = env!("CARGO_PKG_VERSIO");
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: there is a similar Cargo environment variable: `CARGO_PKG_VERSION`
+
+error: environment variable `MY_CUSTOM_VAR` not defined at compile time
+  --> $DIR/env-cargo-var-typo-issue-148439.rs:38:13
+   |
+LL |     let _ = env!("MY_CUSTOM_VAR");
+   |             ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `std::env::var("MY_CUSTOM_VAR")` to read the variable at run time
+
+error: environment variable `CARGO_SOMETHING_TOTALLY_UNKNOWN` not defined at compile time
+  --> $DIR/env-cargo-var-typo-issue-148439.rs:45:13
+   |
+LL |     let _ = env!("CARGO_SOMETHING_TOTALLY_UNKNOWN");
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: Cargo sets build script variables at run time. Use `std::env::var("CARGO_SOMETHING_TOTALLY_UNKNOWN")` instead
+
+error: aborting due to 7 previous errors
+