message: Clarify fingerprint log messages
diff: @@ -817,9 +817,9 @@ impl Fingerprint {
  }
  if self.features != old.features {
  bail!(
  - "features have changed: {} != {}",
  - self.features,
  - old.features
  + "features have changed: previously {}, now {}",
  + old.features,
  + self.features
  )
  }
  if self.target != old.target {
  @@ -833,9 +833,9 @@ impl Fingerprint {
  }
  if self.rustflags != old.rustflags {
  bail!(
  - "RUSTFLAGS has changed: {:?} != {:?}",
  - self.rustflags,
  - old.rustflags
  + "RUSTFLAGS has changed: previously {:?}, now {:?}",
  + old.rustflags,
  + self.rustflags
  )
  }
  if self.metadata != old.metadata {
  @@ -853,7 +853,7 @@ impl Fingerprint {
  match (new, old) {
  (LocalFingerprint::Precalculated(a), LocalFingerprint::Precalculated(b)) => {
  if a != b {
  - bail!("precalculated components have changed: {} != {}", a, b)
  + bail!("precalculated components have changed: previously {}, now {}", b, a)
  }
  }
  (
  @@ -861,7 +861,7 @@ impl Fingerprint {
  LocalFingerprint::CheckDepInfo { dep_info: bdep },
  ) => {
  if adep != bdep {
  - bail!("dep info output changed: {:?} != {:?}", adep, bdep)
  + bail!("dep info output changed: previously {:?}, now {:?}", bdep, adep)
  }
  }
  (
  @@ -875,13 +875,13 @@ impl Fingerprint {
  },
  ) => {
  if aout != bout {
  - bail!("rerun-if-changed output changed: {:?} != {:?}", aout, bout)
  + bail!("rerun-if-changed output changed: previously {:?}, now {:?}", bout, aout)
  }
  if apaths != bpaths {
  bail!(
  - "rerun-if-changed output changed: {:?} != {:?}",
  - apaths,
  + "rerun-if-changed output changed: previously {:?}, now {:?}",
  bpaths,
  + apaths,
  )
  }
  }
  @@ -896,11 +896,11 @@ impl Fingerprint {
  },
  ) => {
  if *akey != *bkey {
  - bail!("env vars changed: {} != {}", akey, bkey);
  + bail!("env vars changed: previously {}, now {}", bkey, akey);
  }
  if *avalue != *bvalue {
  bail!(
  - "env var `{}` changed: previously {:?} now {:?}",
  + "env var `{}` changed: previously {:?}, now {:?}",
  akey,
  bvalue,
  avalue
  