Add a config option to suppress "license was not encountered" warnings

.gitattributes

@@ -1 +1,2 @@
 * text eol=lf
+*.zstd -text

docs/src/checks/licenses/cfg.md

@@ -235,3 +235,11 @@ private = { ignore = true, registries = ["sauce"] }
 ```
 
 [SPDX-expr]: https://spdx.org/spdx-specification-21-web-version#h.jxpfx0ykyb60
+
+### The `unused-allowed-license` field (optional)
+
+Determines what happens when one of the licenses that appears in the `allow` list is not encountered in the dependency graph.
+
+* `warn` (default) - A warning is emitted for each license that appears in `license.allow` but which is not used in any crate.
+* `allow` - Unused licenses in the `licenses.allow` list are ignored.
+* `deny` - An unused license in the `licenses.allow` list triggers an error, and cause the license check to fail.

docs/src/checks/licenses/diags.md

@@ -23,3 +23,5 @@ A [`licenses.exception`](cfg.md#the-exceptions-field-optional) was not used as t
 ### `L006` - license was not encountered
 
 A license in [`licenses.allow`](cfg.md#the-allow-and-deny-fields-optional) was not found in any crate.
+
+This diagnostic can be silenced by configuring the [`licenses.unused-allowed-license`](cfg.md#the-unused-allowed-license-field-optional) field to "allow".

src/licenses.rs

@@ -354,7 +354,7 @@ pub fn check(
     {
         let mut pack = Pack::new(Check::Licenses);
 
-        // Print out warnings for allowed licenses that weren't encountered.
+        // Print diagnostics for allowed licenses that weren't encountered.
         // Note that we don't do the same for denied licenses
         for allowed in hits
             .allowed
@@ -363,6 +363,7 @@ pub fn check(
             .filter_map(|(hit, allowed)| if !hit { Some(allowed) } else { None })
         {
             pack.push(diags::UnmatchedLicenseAllowance {
+                severity: ctx.cfg.unused_allowed_license.into(),
                 allowed_license_cfg: CfgCoord {
                     file: ctx.cfg.file_id,
                     span: allowed.span,

src/licenses/cfg.rs

@@ -155,6 +155,10 @@ pub struct Config {
     /// Licenses that will be allowed in a license expression
     #[serde(default)]
     pub allow: Vec<Spanned<String>>,
+    /// Determines the response to licenses in th `allow`ed list which do not
+    /// exist in the dependency tree.
+    #[serde(default = "crate::lint_warn")]
+    pub unused_allowed_license: LintLevel,
     /// Overrides the license expression used for a particular crate as long as
     /// it exactly matches the specified license files and hashes
     #[serde(default)]
@@ -173,6 +177,7 @@ impl Default for Config {
             allow_osi_fsf_free: BlanketAgreement::default(),
             copyleft: LintLevel::Warn,
             default: LintLevel::Deny,
+            unused_allowed_license: LintLevel::Warn,
             confidence_threshold: confidence_threshold(),
             deny: Vec::new(),
             allow: Vec::new(),
@@ -294,6 +299,7 @@ impl crate::cfg::UnvalidatedConfig for Config {
             unlicensed: self.unlicensed,
             copyleft: self.copyleft,
             default: self.default,
+            unused_allowed_license: self.unused_allowed_license,
             allow_osi_fsf_free: self.allow_osi_fsf_free,
             confidence_threshold: self.confidence_threshold,
             clarifications,
@@ -330,6 +336,7 @@ pub struct ValidConfig {
     pub private: Private,
     pub unlicensed: LintLevel,
     pub copyleft: LintLevel,
+    pub unused_allowed_license: LintLevel,
     pub allow_osi_fsf_free: BlanketAgreement,
     pub default: LintLevel,
     pub confidence_threshold: f32,
@@ -363,6 +370,7 @@ mod test {
         assert_eq!(validated.private.registries, vec!["sekrets".to_owned()]);
         assert_eq!(validated.unlicensed, LintLevel::Warn);
         assert_eq!(validated.copyleft, LintLevel::Deny);
+        assert_eq!(validated.unused_allowed_license, LintLevel::Warn);
         assert_eq!(validated.default, LintLevel::Warn);
         assert_eq!(validated.allow_osi_fsf_free, BlanketAgreement::Both);
         assert_eq!(
@@ -398,7 +406,7 @@ mod test {
                     path: p.fake(),
                     hash: 0xbd0e_ed23,
                 }],
-                expr_offset: 432,
+                expr_offset: 464,
             }]
         );
     }

src/licenses/diags.rs

@@ -50,12 +50,13 @@ impl Into<Diag> for UnmatchedLicenseException {
 }
 
 pub(crate) struct UnmatchedLicenseAllowance {
+    pub(crate) severity: Severity,
     pub(crate) allowed_license_cfg: CfgCoord,
 }
 
 impl Into<Diag> for UnmatchedLicenseAllowance {
     fn into(self) -> Diag {
-        Diagnostic::new(Severity::Warning)
+        Diagnostic::new(self.severity)
             .with_message("license was not encountered")
             .with_code("L006")
             .with_labels(vec![self

tests/cfg/licenses.toml

@@ -3,6 +3,7 @@ unlicensed = "warn"
 allow-osi-fsf-free = "both"
 copyleft = "deny"
 default = "warn"
+unused-allowed-license = "warn"
 confidence-threshold = 0.95
 deny = [
     "Nokia",